Benedetta Carlotti | University of Perugia (original) (raw)

Papers by Benedetta Carlotti

Phys. Chem. Chem. Phys., 2015

ABSTRACT A joint experimental and theoretical approach, involving state-of-the-art femtosecond fl... more ABSTRACT A joint experimental and theoretical approach, involving state-of-the-art femtosecond fluorescence up-conversion measurements and quantum mechanical computations including vibronic effects, was employed to get a deep insight into the excited state dynamics of two cationic dipolar chromophores (Donor−π−Acceptor+) where the electron deficient portion is a N-methyl pyridinium and the electron donor a trimethoxyphenyl or a pyrene, respectively. The ultrafast spectroscopic investigation, and the Time Resolved Area Normalised Emission Spectra in particular, revealed a peculiar multiple emissive behaviour and allowed distinct emitting states to be remakably distinguished from solvation dynamics, occurring in water in a similar time scale. The two and three emissions experimentally detected for the trimethoxyphenyl and pyrene derivatives, respectively, were associated to specific local emissive minima in the potential energy surface of S1 on the ground of quantum−mechanical calculations. A low polar and planar Locally Excited (LE) state together with a highly polar and Twisted Intramolecular Charge Transfer (TICT) state are identified as responsible for the dual emission of the trimethoxyphenyl compound. Interestingly, the more complex photobehaviour of the pyrenyl derivative was explained considering the contribution to the fluorescence coming not only from the LE and TICT states but also from a nearly Planar Intramolecular Charge Transfer (PICT) state, being both the TICT and the PICT generated from LE by progressive torsion around the quasi single bond between the methylpyridinium and the ethene bridge. These findings point to an interconversion between rotamers for the pyrene compound taking place in its excited state against the Non Equilibrated Excited Rotamers (NEER) principle.

The Journal of Physical Chemistry A, 2014

The solvent effect on the photophysical and photochemical 10 properties of the iodides of three t... more The solvent effect on the photophysical and photochemical 10 properties of the iodides of three trans (E) isomers of 2-D-vinyl,1-11 methylpyridinium, where D is a donor group (4-dimethylaminophenyl, 12 3,4,5-trimethoxyphenyl and 1-pyrenyl), was studied by stationary and 13 transient absorption techniques. The results obtained allowed the negative 14 solvatochromism and relaxation pathways of the excited states in the 15 singlet manifold to be reasonably interpreted. Resorting to ultrafast 16 absorption techniques and DFT calculations allowed information on the 17 excited state dynamics and the role of the solvent-controlled intramolecular 18 charge transfer (ICT) processes to be obtained. The structure-dependent 19 excited state dynamics in nonpolar solvents, where the ICT is slower than 20 solvent rearrangement, and in polar solvents, where an opposite situation is 21 operative, was thus explained. The push−pull character of the three 22 compounds, particularly the anilino-derivative, suggests their potential 23 application in optoelectronics. s1 48 trimethoxyphenyl (2) and 1-pyrenyl (3)] (Scheme 1), were 49 investigated by stationary and transient absorption techniques 50 and DFT calculations. The photobehavior of the polar 1 51 (usually named by its acronym o-DASPMI) and its positional 52 isomer p-DASPMI, were previously studied in various 53 laboratories by stationary and ultrafast spectroscopic techni-54 ques. 9,16−30 For 1, a negative solvatochromism and a very 55 modest, if any, positive fluosolvatochromism were reported. 56 The solvent-dependent excited state dynamics, which involves 57 internal rotation around double (cis−trans isomerization) and 58 single (formation of twisted rotamers) bonds, was discussed 59 using different approaches. Some authors mainly emphasized 60 the effects of solvent dynamics reflected by the fastest decay 61 components 25,26,28,29 while others gave more attention to the 62 concomitant evolution of the excited solute on the basis of a 63 three-state model. 23,24,27 These authors attributed the multi-64 exponential emission specifically to the contributions of the 65 locally excited (LE) state, formed by the relaxation of the 66 Franck−Condon state and precursor of a second state (still 67 planar), produced by further intramolecular charge transfer 68 (ICT), generally favored in polar solvents, and a successive 69 third state formed in polar solvents by the twisting of the p-70 dimethylanilino or N-methylpyridinium group around the 71 quasi-single bond with the ethene bridge (TICT). 23,24,27 As 72 pointed out in previous papers 23,29 both aspects, the relaxation A dx.doi.org/10.1021/jp407342q | J. Phys. Chem. A XXXX, XXX, XXX−XXX kbg00 | ACSJCA | JCA10.0.1465/W Unicode | research.3f (R3.6.i5 HF01:4227 | 2.0 alpha 39) 2014/03/19 08:04:00 | PROD-JCAVA | rq_3479297 | 5/05/2014 15:49:41 | 13 | JCA-DEFAULT 73 of solvent dipoles and the detection of several emitting states, 74 have to be taken into account when describing the emission 75 properties of these kind of dyes. 76

The Journal of Physical Chemistry B, 2015

Photophysical properties of some azinium iodides in aqueous solution of nanostructured systems as... more Photophysical properties of some azinium iodides in aqueous solution of nanostructured systems as DNA and nonionic micelles were investigated using steady-state and ultrafast time-resolved spectroscopy. Spectrophotometric and fluorimetric titrations of the investigated compounds with salmon testes DNA supplied evidence of a good interaction between the salts and DNA with binding constants of 10(4)-10(6) M(-1), making them interesting for pharmaceutical applications. The interaction with DNA also changes the photobehavior of the compounds, increasing the radiative deactivation pathway to the detriment of internal conversion and slowing down the excited state dynamics. The interaction of the azinium salts with the nonionic surfactant Triton X-100 from premicellar to postmicellar concentration was studied by spectrophotometric and fluorimetric titrations evidencing the ability of the micelles to associate the studied salts in their hydrophobic portion and to release them in the presence of DNA, acting as promising drug carriers. Also transient absorption spectroscopy with femtosecond resolution demonstrated the insertion of the investigated compounds into micellar aggregates. Preliminary measurements by confocal fluorescence microscopy on MCF-7 cells in the presence of the studied azinium salts showed that they are able to cross the cellular membrane and that their cytotoxicity can be expressed through interaction with DNA (RNA). In fact, they showed a significant fluorescence signal in all cell compartments, particularly (for 2 and 3) into punctuate structures within the nuclei compatible with a localization into the nucleoli.

Journal of Photochemistry and Photobiology A-chemistry, 2011

Four novel trans,trans-2,5-distyrylfuran derivatives (E,E-X-DStFs, X=Cl, OCH3, N(CH3)2, NO2) have... more Four novel trans,trans-2,5-distyrylfuran derivatives (E,E-X-DStFs, X=Cl, OCH3, N(CH3)2, NO2) have been synthesized and characterized by 1H and 13C NMR and UV–vis spectroscopy. The photophysical properties of the excited states of these poorly photoreactive compounds have been studied in two solvents of different polarities by stationary and pulsed techniques and also by the help of semiempirical quantum-mechanical calculations. The high fluorescence

Femtosecond time-resolved absorption and fluorescence spectroscopy have been used to probe the ex... more Femtosecond time-resolved absorption and fluorescence spectroscopy have been used to probe the excited-state reaction of the antimalarial quinacrine (QC) in order to obtain a better understanding of the excited states of the molecule. All the measurements were performed by using 40 fs visible pump pulses with a centre wavelength of 400 nm in buffered solutions at different pHs. The excitation

Journal of Photochemistry and Photobiology A: Chemistry, 2015

ABSTRACT A comprehensive investigation of the photophysics of cyanophenylpyrrole derivatives has ... more ABSTRACT A comprehensive investigation of the photophysics of cyanophenylpyrrole derivatives has been carried out by means of steady-state, nanosecond and femtosecond resolved absorption and fluorescence techniques, and quantum–mechanical calculations. This study revealed that the investigated compounds (1–3) are highly fluorescent molecules (ΦF = 0.2–0.9) with lifetimes in the range 2–8 ns. The compounds exhibit weak hypsochromic solvatochromic changes in the absorption and large batochromic shifts in the fluorescence spectra. An increase in solvent polarity does not induce a reduction of the fluorescence quantum yields, but causes a lengthening of the fluorescence lifetimes. The density functional theoretical calculations predicted similar energies for S1 and S2, probably resulting in the state mixing and ICT character of the relaxed S1 state. Furthermore, the computed dipole moments have been found to be higher in the excited with respect to the ground state, in agreement with the strong solvatochromic properties experimentally observed in the emission spectra. Ultrafast transient absorption measurements indicated the existence of three decay components assigned to the hot Franck–Condon S1 state that undergoes vibrational cooling (VC, several picoseconds), the species formed by VC undergoing a torsional motion of the CC bond between the phenyl and the pyrrole ring (several hundreds of picoseconds), and the relaxed S1 state that decays radiatively (nanoseconds). Indeed, the calculated optimized geometry of 1–3 in the ground state is characterized by a dihedral angle between the pyrrole and phenyl moieties of about 10–25°, whereas the S1 state is predicted to be more planar than S0. Due to the fast population of the relaxed S1 states, the typical dual fluorescence reported for N-phenylpyrroles was not observed for 1–3.

The Journal of Physical Chemistry B, 2015

Two N-methylpyridinium salts with push-pull properties have been investigated in the aqueous solu... more Two N-methylpyridinium salts with push-pull properties have been investigated in the aqueous solution of anionic micelles of sodium dodecyl sulfate (SDS) and potassium p-(octyloxy)benzenesulfonate (pOoBSK) surfactants. These molecules are known to be extremely sensitive to the local environment, with their absorption spectrum being subjected to a net negative solvatochromism. These compounds are also characterized by an excited state deactivation strictly dependent on the physical properties of the chemical surrounding, with the formation of intramolecular charge-transfer (ICT) states accordingly stabilized. Thanks to steady-state and femtosecond resolved spectroscopic techniques, the photophysical properties of these molecules in the presence of anionic micelles have been fully characterized and an efficient permeation within the micellar aggregates can thus be inferred. The extent of the changes in the photophysical properties of these molecules (with respect to what is observed in water) is an indicator of the medium experienced in the nanoheterogeneous solutions: enhanced fluorescence emissions, reduced Stokes shifts and slowed-down excited state decays strongly confirm the confinement within a scarcely polar and restraining environment. The slightly different behavior shown in the two types of micelles can be ascribed to a peculiar interaction between the aromatic moiety of the surfactant and that of the cations. Additionally, the inclusion promotes the solubilization of these poorly water-soluble salts, which is alluring in their promising use as DNA binders for antitumor purposes. Thus, the anionic micelles allowed the solubilization of the pyridinium salts under investigation, which in turn allowed the characterization of the nonhomogeneous medium established by the micellar aggregates.

The journal of physical chemistry. B, Jan 22, 2015

The long-standing controversy about the presence of two different emissive minima in the lowest e... more The long-standing controversy about the presence of two different emissive minima in the lowest excited state of the cationic push-pull dye DASPMI was definitively proved through the observation of dual emission, evidenced by both experimental (femtosecond up-conversion measurements) and theoretical (Density Functional Theory calculations) approaches. From the fluorescence up-conversion data of DASPMI in water the Time Resolved Area Normalized Spectra (TRANES) were calculated, showing one isoemissive point and therefore revealing the presence of two distinct emissive minima of the excited state potential energy hyper-surface with lifetimes of 0.51 and 4.8 ps. These spectroscopic techniques combined with proper data analysis allowed us to discriminate the sub-picosecond emitting state from the occurrence of ultrafast solvation dynamics and to disentangle the overlapping fluorescence (very close in energy) of the two components. Vibronic computations based on TD-DFT potential energy s...

Physical chemistry chemical physics : PCCP, Jan 14, 2014

Oxytetracycline (OX) and doxycycline (DX) are antibiotics belonging to the family of tetracycline... more Oxytetracycline (OX) and doxycycline (DX) are antibiotics belonging to the family of tetracyclines. We present a UV-Visible steady state and time-resolved experimental study of OX and DX and their biologically active Mg(2+) complexes loaded within a hydrogel matrix. Hydrogels are a three dimensional network of worm-like micelles, mutually intertwined, forming a pattern of hydrophobic domains and water pools. We resorted to a hydrogel, made of a zwitterionic N-oxide surfactant (p-dodecyloxybenzyldimethylamine N-oxide, pDoAO), which showed promising features as a drug vehicle. The spectral and photophysical properties of the drugs are significantly altered by the inclusion in the hydrophobic domains of the gel and these variations are indicators of the permeation ratio of the drug in between the micelles forming the gel network. We thus get a clear picture of the distribution of the drug molecules and metal chelates into the two different kinds of environment, where the hydrophobic do...

Physical chemistry chemical physics : PCCP, Jan 21, 2015

We report here experimental evidence of dual emission in a cationic push-pull system (bearing a m... more We report here experimental evidence of dual emission in a cationic push-pull system (bearing a methyl pyridinium group as an electron acceptor and a diphenylamino group as an electron donor), which shows negative solvatochromism. An intriguing blue shift and enlargement of the fluorescence band upon increasing the solvent polarity have suggested a possible contribution of an upper excited state to the stationary emission. Ultrafast transient absorption has indeed revealed the presence of an intermediate transient species in some solvents. The investigation of the fluorescence properties at low temperatures and in the rigid matrix has given a clear indication of this additional emission at shorter wavelengths. Femtosecond up-conversion measurements have shown interesting rise-decay dynamics in the kinetics and two well distinguished emission bands characterized by different deactivations. A single isoemissive point in the time-resolved area-normalized spectra has unambiguously point...

ChemPhysChem, 2015

Il presente documento viene fornito attraverso il servizio NILDE dalla Biblioteca fornitrice, nel... more Il presente documento viene fornito attraverso il servizio NILDE dalla Biblioteca fornitrice, nel rispetto della vigente normativa sul Diritto d'Autore (Legge n.633 del 22/4/1941 modifiche e integrazioni) e delle clausole contrattuali in essere con il titolare dei diritti di proprietà intellettuale.

The Journal of Physical Chemistry A, 2015

The effects of pH on the spectral properties of stilbazolium salts bearing dimethylamino substitu... more The effects of pH on the spectral properties of stilbazolium salts bearing dimethylamino substituents, namely, trans isomers of the iodides of the dipolar E-[2-(4dimethylamino)styryl]-1-methylpyridinium, its branched quadrupolar analogue E,E-[2,6-di-(p-dimethylamino)styryl]-1-methylpyridinium, and three analogues, chosen to investigate the effects of the stronger quinolinium acceptor, the longer butadiene π bridge, or both, were investigated through a joint experimental and computational approach. A noticeable acidochromism of the absorption spectra (interesting for applications) was observed, with the basic and protonated species giving intensely colored and transparent solutions, respectively. The acid−base equilibrium constants for the protonation of the dimethylamino group in the ground state (pK a ) were experimentally derived. Theoretical calculations according to the thermodynamic Born− Haber cycle provided pK a values in good agreement with the experimental values. The very low fluorescence yield did not allow a direct investigation of the changes in the acid−base properties in the excited state (pK a *) by fluorimetric titrations. Their values were derived by quantum-mechanical calculations and estimated experimentally on the basis of the Forster cycle.

Tetracyclines are a class of derivatives of polycyclic naphthacene carboxamide, which have attrac... more Tetracyclines are a class of derivatives of polycyclic naphthacene carboxamide, which have attracted wide interest in the pharmaceutical field for their use as antibiotics. These molecules are characterized by a substantial conformational flexibility and by the presence of different binding sites which endow tetracycline with a noticeable capability in binding biological targets. A salient property of tetracyclines is the presence of multiple acidic groups: four equilibrium constants have been measured for the fully protonated tetracycline (TCH 3 ? ) but so far no clear information concerning the pK a s of the various sites has been reported. We present here a computational investigation on the correlation between the acid-base and the spectroscopic properties of this important class of compounds. Starting from the TCH 3 ? species, the pK a of all the possible deprotonation sites has been computed by DFT calculations. The computed pK a s nicely compare with the experimental data, within 1 pK a unit, allowing us to individuate the products of the first deprotonation. This procedure has been iteratively repeated using as starting species the products singled out from the previous deprotonation, thus individuating the stepwise products of each deprotonation step. Then, the optical absorption spectra have been computed for all the species involved in the protonation/deprotonation equilibria, comparing the results with the experimental data. The good agreement between theory and experiment has allowed us to rationalize the correlation between the solution pH and the absorption spectra.

We report the photobehaviour of a series of eight structurally related arylacetylene derivatives,... more We report the photobehaviour of a series of eight structurally related arylacetylene derivatives, in solution as well as in pristine and PC BM blended thin-lms. The formation of both H-and J-aggregates in the solid state have been demonstrated, and, interestingly, an energy transfer from H-aggregates or/and from residual "unstacked" molecules to J-aggregates has been found, the latter being the only emitting species. The uorescence quenching by PC BM at di erent loadings has been studied in blend lms, and it has been found particularly ecient in the case of a symmetrical peripheral substitution of the acetylene derivative core. Preliminary time-resolved measurements in emission (ns resolution) and in absorption (fs resolution) con rmed the H→J energy transfer and underlined the presence of delayed uorescence from Jaggregates, formed by energy transfer from the long-lived rst excited singlet state of H-aggregates. In all cases, a homogeneous surface morphology of thin-lms was identied by confocal uorescence microscopy.

Nanoparticles were prepared in different experimental conditions by a re-precipitation method by ... more Nanoparticles were prepared in different experimental conditions by a re-precipitation method by use of perylene and polyvinylalcohol as active material and stabilizer, respectively. The excitation and emission spectral properties of dispersions in aqueous solutions of the various samples were recorded together with the fluorescence quantum yields and lifetimes (where detectable). The experimental results are consistent with the formation of excimer-like states, responsible of the emission properties, in the nanoparticles. Confocal fluorescence and atomic force (AFM) microscopies were able to give information on the fluorescence properties and size distribution (most probable size of 3 -5 nm) of the nanoparticles.

www.rsc.org/dalton PAPER Acid-base properties of the N3 ruthenium(II) solar cell sensitizer: a co... more www.rsc.org/dalton PAPER Acid-base properties of the N3 ruthenium(II) solar cell sensitizer: a combined experimental and computational analysis † We report a combined spectro-photometric and computational investigation of the acid-base equilibria of the N3 solar cell sensitizer [Ru(dcbpyH 2 ) 2 (NCS) 2 ] (dcbpyH 2 = 4,4′-dicarboxyl-2,2′ bipyridine) in aqueous/ethanol solutions. The absorption spectra of N3 recorded at various pH values were analyzed by Single Value Decomposition techniques, followed by Global Fitting procedures, allowing us to identify four separate acid-base equilibria and their corresponding ground state pK a values. DFT/TDDFT calculations were performed for the N3 dye in solution, investigating the possible relevant species obtained by sequential deprotonation of the four dye carboxylic groups. TDDFT excited state calculations provided UV-vis absorption spectra which nicely agree with the experimental spectral shapes at various pH values. The calculated pK a values are also in good agreement with experimental data, within <1 pK a unit. Based on the calculated energy differences a tentative assignment of the N3 deprotonation pathway is reported. † Electronic supplementary information (ESI) available: Molecular orbitals energy, absorption spectra in water solution and computed pK a values. Schematic representation of the deprotonation path of N3H 4 together with the pK a values calculated by the SPH method. The structures leading to the lower pK a pathway are highlighted.

Physical Chemistry Chemical Physics, 2014

We report here a joint experimental and theoretical study of a quadrupolar, two-branched pyridini... more We report here a joint experimental and theoretical study of a quadrupolar, two-branched pyridinium derivative of interest as a potential non-linear optical material. The spectral and photophysical behaviour of this symmetric system is greatly affected by the polarity of the medium. A very efficient photoinduced intramolecular charge transfer, surprisingly more efficient than in the dipolar asymmetric analogue, is found to occur by femtosecond resolved transient absorption spectroscopy. TD-DFT calculations are in excellent agreement with these experimental findings and predict large charge displacements in the molecular orbitals describing the ground state and the lowest excited singlet state. The theoretical study also revealed that in highly polar media the symmetry of the excited state is broken giving a possible explanation to the fluorescence and transient absorption spectra resembling those of the one-branched analogous compound in the same solvents. The present study may give an important insight into the excited state deactivation mechanism of cationic (donor-p-acceptor-p-donor) + quadrupolar compounds characterised by negative solvatochromism, which are expected to show significant two-photon absorption (TPA). Moreover, the water solubility of the investigated quadrupolar system may represent an added value in view of the most promising applications of TPA materials in biology and medicine.

Journal of Physical Chemistry B, 2014

This work presents a steady-state and time-resolved UV−visible spectroscopic investigation of two... more This work presents a steady-state and time-resolved UV−visible spectroscopic investigation of two antibiotics belonging to the family of tetracyclines (doxycycline and oxytetracycline) in the micellar medium provided by p-dodecyloxybenzyltrimethylammonium bromide (pDoTABr). The spectroscopic analysis has been performed in absorption and emission with femtosecond time resolution, and at pH 5.0 and 8.7 where doxycycline and oxytetracycline are present in their neutral-zwitterionic and monoanionic forms, respectively. The experimental data have been processed by sophisticated data mining methods such as global/ target analysis and the maximum entropy method. The results unambiguously indicate that, when doxycycline and oxytetracycline are in their zwitterionic form, they are entrapped within the micelle, while when they are in their monoanionic form, they preferentially show a strong one-to-one interaction with the positively charged surfactant heads. Thus, the pH of the solution controls the inclusion of the investigated drugs into the micelle. When the drugs are entrapped inside the micelles, their spectroscopic and dynamical properties after photoexcitation change appreciably. Interestingly, the entrapped drugs are still able to strongly bind Mg 2+ cations, crucial in determining the biological functioning of tetracyclines. The femtosecond resolved measurements reveal that the drugs are efficiently pulled out of the micelles by Mg 2+ . In fact, magnesium−tetracycline complexes are detected in the aqueous phase. The present study suggests the potential promising use of ammonium surfactant micelles embedding doxycycline and oxytetracycline as "smart" drug delivery systems allowing their pH controlled inclusion and Mg 2+ induced release.

Phys. Chem. Chem. Phys., 2015

ABSTRACT A joint experimental and theoretical approach, involving state-of-the-art femtosecond fl... more ABSTRACT A joint experimental and theoretical approach, involving state-of-the-art femtosecond fluorescence up-conversion measurements and quantum mechanical computations including vibronic effects, was employed to get a deep insight into the excited state dynamics of two cationic dipolar chromophores (Donor−π−Acceptor+) where the electron deficient portion is a N-methyl pyridinium and the electron donor a trimethoxyphenyl or a pyrene, respectively. The ultrafast spectroscopic investigation, and the Time Resolved Area Normalised Emission Spectra in particular, revealed a peculiar multiple emissive behaviour and allowed distinct emitting states to be remakably distinguished from solvation dynamics, occurring in water in a similar time scale. The two and three emissions experimentally detected for the trimethoxyphenyl and pyrene derivatives, respectively, were associated to specific local emissive minima in the potential energy surface of S1 on the ground of quantum−mechanical calculations. A low polar and planar Locally Excited (LE) state together with a highly polar and Twisted Intramolecular Charge Transfer (TICT) state are identified as responsible for the dual emission of the trimethoxyphenyl compound. Interestingly, the more complex photobehaviour of the pyrenyl derivative was explained considering the contribution to the fluorescence coming not only from the LE and TICT states but also from a nearly Planar Intramolecular Charge Transfer (PICT) state, being both the TICT and the PICT generated from LE by progressive torsion around the quasi single bond between the methylpyridinium and the ethene bridge. These findings point to an interconversion between rotamers for the pyrene compound taking place in its excited state against the Non Equilibrated Excited Rotamers (NEER) principle.

The Journal of Physical Chemistry A, 2014

The solvent effect on the photophysical and photochemical 10 properties of the iodides of three t... more The solvent effect on the photophysical and photochemical 10 properties of the iodides of three trans (E) isomers of 2-D-vinyl,1-11 methylpyridinium, where D is a donor group (4-dimethylaminophenyl, 12 3,4,5-trimethoxyphenyl and 1-pyrenyl), was studied by stationary and 13 transient absorption techniques. The results obtained allowed the negative 14 solvatochromism and relaxation pathways of the excited states in the 15 singlet manifold to be reasonably interpreted. Resorting to ultrafast 16 absorption techniques and DFT calculations allowed information on the 17 excited state dynamics and the role of the solvent-controlled intramolecular 18 charge transfer (ICT) processes to be obtained. The structure-dependent 19 excited state dynamics in nonpolar solvents, where the ICT is slower than 20 solvent rearrangement, and in polar solvents, where an opposite situation is 21 operative, was thus explained. The push−pull character of the three 22 compounds, particularly the anilino-derivative, suggests their potential 23 application in optoelectronics. s1 48 trimethoxyphenyl (2) and 1-pyrenyl (3)] (Scheme 1), were 49 investigated by stationary and transient absorption techniques 50 and DFT calculations. The photobehavior of the polar 1 51 (usually named by its acronym o-DASPMI) and its positional 52 isomer p-DASPMI, were previously studied in various 53 laboratories by stationary and ultrafast spectroscopic techni-54 ques. 9,16−30 For 1, a negative solvatochromism and a very 55 modest, if any, positive fluosolvatochromism were reported. 56 The solvent-dependent excited state dynamics, which involves 57 internal rotation around double (cis−trans isomerization) and 58 single (formation of twisted rotamers) bonds, was discussed 59 using different approaches. Some authors mainly emphasized 60 the effects of solvent dynamics reflected by the fastest decay 61 components 25,26,28,29 while others gave more attention to the 62 concomitant evolution of the excited solute on the basis of a 63 three-state model. 23,24,27 These authors attributed the multi-64 exponential emission specifically to the contributions of the 65 locally excited (LE) state, formed by the relaxation of the 66 Franck−Condon state and precursor of a second state (still 67 planar), produced by further intramolecular charge transfer 68 (ICT), generally favored in polar solvents, and a successive 69 third state formed in polar solvents by the twisting of the p-70 dimethylanilino or N-methylpyridinium group around the 71 quasi-single bond with the ethene bridge (TICT). 23,24,27 As 72 pointed out in previous papers 23,29 both aspects, the relaxation A dx.doi.org/10.1021/jp407342q | J. Phys. Chem. A XXXX, XXX, XXX−XXX kbg00 | ACSJCA | JCA10.0.1465/W Unicode | research.3f (R3.6.i5 HF01:4227 | 2.0 alpha 39) 2014/03/19 08:04:00 | PROD-JCAVA | rq_3479297 | 5/05/2014 15:49:41 | 13 | JCA-DEFAULT 73 of solvent dipoles and the detection of several emitting states, 74 have to be taken into account when describing the emission 75 properties of these kind of dyes. 76

The Journal of Physical Chemistry B, 2015

Photophysical properties of some azinium iodides in aqueous solution of nanostructured systems as... more Photophysical properties of some azinium iodides in aqueous solution of nanostructured systems as DNA and nonionic micelles were investigated using steady-state and ultrafast time-resolved spectroscopy. Spectrophotometric and fluorimetric titrations of the investigated compounds with salmon testes DNA supplied evidence of a good interaction between the salts and DNA with binding constants of 10(4)-10(6) M(-1), making them interesting for pharmaceutical applications. The interaction with DNA also changes the photobehavior of the compounds, increasing the radiative deactivation pathway to the detriment of internal conversion and slowing down the excited state dynamics. The interaction of the azinium salts with the nonionic surfactant Triton X-100 from premicellar to postmicellar concentration was studied by spectrophotometric and fluorimetric titrations evidencing the ability of the micelles to associate the studied salts in their hydrophobic portion and to release them in the presence of DNA, acting as promising drug carriers. Also transient absorption spectroscopy with femtosecond resolution demonstrated the insertion of the investigated compounds into micellar aggregates. Preliminary measurements by confocal fluorescence microscopy on MCF-7 cells in the presence of the studied azinium salts showed that they are able to cross the cellular membrane and that their cytotoxicity can be expressed through interaction with DNA (RNA). In fact, they showed a significant fluorescence signal in all cell compartments, particularly (for 2 and 3) into punctuate structures within the nuclei compatible with a localization into the nucleoli.

Journal of Photochemistry and Photobiology A-chemistry, 2011

Four novel trans,trans-2,5-distyrylfuran derivatives (E,E-X-DStFs, X=Cl, OCH3, N(CH3)2, NO2) have... more Four novel trans,trans-2,5-distyrylfuran derivatives (E,E-X-DStFs, X=Cl, OCH3, N(CH3)2, NO2) have been synthesized and characterized by 1H and 13C NMR and UV–vis spectroscopy. The photophysical properties of the excited states of these poorly photoreactive compounds have been studied in two solvents of different polarities by stationary and pulsed techniques and also by the help of semiempirical quantum-mechanical calculations. The high fluorescence

Femtosecond time-resolved absorption and fluorescence spectroscopy have been used to probe the ex... more Femtosecond time-resolved absorption and fluorescence spectroscopy have been used to probe the excited-state reaction of the antimalarial quinacrine (QC) in order to obtain a better understanding of the excited states of the molecule. All the measurements were performed by using 40 fs visible pump pulses with a centre wavelength of 400 nm in buffered solutions at different pHs. The excitation

Journal of Photochemistry and Photobiology A: Chemistry, 2015

ABSTRACT A comprehensive investigation of the photophysics of cyanophenylpyrrole derivatives has ... more ABSTRACT A comprehensive investigation of the photophysics of cyanophenylpyrrole derivatives has been carried out by means of steady-state, nanosecond and femtosecond resolved absorption and fluorescence techniques, and quantum–mechanical calculations. This study revealed that the investigated compounds (1–3) are highly fluorescent molecules (ΦF = 0.2–0.9) with lifetimes in the range 2–8 ns. The compounds exhibit weak hypsochromic solvatochromic changes in the absorption and large batochromic shifts in the fluorescence spectra. An increase in solvent polarity does not induce a reduction of the fluorescence quantum yields, but causes a lengthening of the fluorescence lifetimes. The density functional theoretical calculations predicted similar energies for S1 and S2, probably resulting in the state mixing and ICT character of the relaxed S1 state. Furthermore, the computed dipole moments have been found to be higher in the excited with respect to the ground state, in agreement with the strong solvatochromic properties experimentally observed in the emission spectra. Ultrafast transient absorption measurements indicated the existence of three decay components assigned to the hot Franck–Condon S1 state that undergoes vibrational cooling (VC, several picoseconds), the species formed by VC undergoing a torsional motion of the CC bond between the phenyl and the pyrrole ring (several hundreds of picoseconds), and the relaxed S1 state that decays radiatively (nanoseconds). Indeed, the calculated optimized geometry of 1–3 in the ground state is characterized by a dihedral angle between the pyrrole and phenyl moieties of about 10–25°, whereas the S1 state is predicted to be more planar than S0. Due to the fast population of the relaxed S1 states, the typical dual fluorescence reported for N-phenylpyrroles was not observed for 1–3.

The Journal of Physical Chemistry B, 2015

Two N-methylpyridinium salts with push-pull properties have been investigated in the aqueous solu... more Two N-methylpyridinium salts with push-pull properties have been investigated in the aqueous solution of anionic micelles of sodium dodecyl sulfate (SDS) and potassium p-(octyloxy)benzenesulfonate (pOoBSK) surfactants. These molecules are known to be extremely sensitive to the local environment, with their absorption spectrum being subjected to a net negative solvatochromism. These compounds are also characterized by an excited state deactivation strictly dependent on the physical properties of the chemical surrounding, with the formation of intramolecular charge-transfer (ICT) states accordingly stabilized. Thanks to steady-state and femtosecond resolved spectroscopic techniques, the photophysical properties of these molecules in the presence of anionic micelles have been fully characterized and an efficient permeation within the micellar aggregates can thus be inferred. The extent of the changes in the photophysical properties of these molecules (with respect to what is observed in water) is an indicator of the medium experienced in the nanoheterogeneous solutions: enhanced fluorescence emissions, reduced Stokes shifts and slowed-down excited state decays strongly confirm the confinement within a scarcely polar and restraining environment. The slightly different behavior shown in the two types of micelles can be ascribed to a peculiar interaction between the aromatic moiety of the surfactant and that of the cations. Additionally, the inclusion promotes the solubilization of these poorly water-soluble salts, which is alluring in their promising use as DNA binders for antitumor purposes. Thus, the anionic micelles allowed the solubilization of the pyridinium salts under investigation, which in turn allowed the characterization of the nonhomogeneous medium established by the micellar aggregates.

The journal of physical chemistry. B, Jan 22, 2015

The long-standing controversy about the presence of two different emissive minima in the lowest e... more The long-standing controversy about the presence of two different emissive minima in the lowest excited state of the cationic push-pull dye DASPMI was definitively proved through the observation of dual emission, evidenced by both experimental (femtosecond up-conversion measurements) and theoretical (Density Functional Theory calculations) approaches. From the fluorescence up-conversion data of DASPMI in water the Time Resolved Area Normalized Spectra (TRANES) were calculated, showing one isoemissive point and therefore revealing the presence of two distinct emissive minima of the excited state potential energy hyper-surface with lifetimes of 0.51 and 4.8 ps. These spectroscopic techniques combined with proper data analysis allowed us to discriminate the sub-picosecond emitting state from the occurrence of ultrafast solvation dynamics and to disentangle the overlapping fluorescence (very close in energy) of the two components. Vibronic computations based on TD-DFT potential energy s...

Physical chemistry chemical physics : PCCP, Jan 14, 2014

Oxytetracycline (OX) and doxycycline (DX) are antibiotics belonging to the family of tetracycline... more Oxytetracycline (OX) and doxycycline (DX) are antibiotics belonging to the family of tetracyclines. We present a UV-Visible steady state and time-resolved experimental study of OX and DX and their biologically active Mg(2+) complexes loaded within a hydrogel matrix. Hydrogels are a three dimensional network of worm-like micelles, mutually intertwined, forming a pattern of hydrophobic domains and water pools. We resorted to a hydrogel, made of a zwitterionic N-oxide surfactant (p-dodecyloxybenzyldimethylamine N-oxide, pDoAO), which showed promising features as a drug vehicle. The spectral and photophysical properties of the drugs are significantly altered by the inclusion in the hydrophobic domains of the gel and these variations are indicators of the permeation ratio of the drug in between the micelles forming the gel network. We thus get a clear picture of the distribution of the drug molecules and metal chelates into the two different kinds of environment, where the hydrophobic do...

Physical chemistry chemical physics : PCCP, Jan 21, 2015

We report here experimental evidence of dual emission in a cationic push-pull system (bearing a m... more We report here experimental evidence of dual emission in a cationic push-pull system (bearing a methyl pyridinium group as an electron acceptor and a diphenylamino group as an electron donor), which shows negative solvatochromism. An intriguing blue shift and enlargement of the fluorescence band upon increasing the solvent polarity have suggested a possible contribution of an upper excited state to the stationary emission. Ultrafast transient absorption has indeed revealed the presence of an intermediate transient species in some solvents. The investigation of the fluorescence properties at low temperatures and in the rigid matrix has given a clear indication of this additional emission at shorter wavelengths. Femtosecond up-conversion measurements have shown interesting rise-decay dynamics in the kinetics and two well distinguished emission bands characterized by different deactivations. A single isoemissive point in the time-resolved area-normalized spectra has unambiguously point...

ChemPhysChem, 2015

Il presente documento viene fornito attraverso il servizio NILDE dalla Biblioteca fornitrice, nel... more Il presente documento viene fornito attraverso il servizio NILDE dalla Biblioteca fornitrice, nel rispetto della vigente normativa sul Diritto d'Autore (Legge n.633 del 22/4/1941 modifiche e integrazioni) e delle clausole contrattuali in essere con il titolare dei diritti di proprietà intellettuale.

The Journal of Physical Chemistry A, 2015

The effects of pH on the spectral properties of stilbazolium salts bearing dimethylamino substitu... more The effects of pH on the spectral properties of stilbazolium salts bearing dimethylamino substituents, namely, trans isomers of the iodides of the dipolar E-[2-(4dimethylamino)styryl]-1-methylpyridinium, its branched quadrupolar analogue E,E-[2,6-di-(p-dimethylamino)styryl]-1-methylpyridinium, and three analogues, chosen to investigate the effects of the stronger quinolinium acceptor, the longer butadiene π bridge, or both, were investigated through a joint experimental and computational approach. A noticeable acidochromism of the absorption spectra (interesting for applications) was observed, with the basic and protonated species giving intensely colored and transparent solutions, respectively. The acid−base equilibrium constants for the protonation of the dimethylamino group in the ground state (pK a ) were experimentally derived. Theoretical calculations according to the thermodynamic Born− Haber cycle provided pK a values in good agreement with the experimental values. The very low fluorescence yield did not allow a direct investigation of the changes in the acid−base properties in the excited state (pK a *) by fluorimetric titrations. Their values were derived by quantum-mechanical calculations and estimated experimentally on the basis of the Forster cycle.

Tetracyclines are a class of derivatives of polycyclic naphthacene carboxamide, which have attrac... more Tetracyclines are a class of derivatives of polycyclic naphthacene carboxamide, which have attracted wide interest in the pharmaceutical field for their use as antibiotics. These molecules are characterized by a substantial conformational flexibility and by the presence of different binding sites which endow tetracycline with a noticeable capability in binding biological targets. A salient property of tetracyclines is the presence of multiple acidic groups: four equilibrium constants have been measured for the fully protonated tetracycline (TCH 3 ? ) but so far no clear information concerning the pK a s of the various sites has been reported. We present here a computational investigation on the correlation between the acid-base and the spectroscopic properties of this important class of compounds. Starting from the TCH 3 ? species, the pK a of all the possible deprotonation sites has been computed by DFT calculations. The computed pK a s nicely compare with the experimental data, within 1 pK a unit, allowing us to individuate the products of the first deprotonation. This procedure has been iteratively repeated using as starting species the products singled out from the previous deprotonation, thus individuating the stepwise products of each deprotonation step. Then, the optical absorption spectra have been computed for all the species involved in the protonation/deprotonation equilibria, comparing the results with the experimental data. The good agreement between theory and experiment has allowed us to rationalize the correlation between the solution pH and the absorption spectra.

We report the photobehaviour of a series of eight structurally related arylacetylene derivatives,... more We report the photobehaviour of a series of eight structurally related arylacetylene derivatives, in solution as well as in pristine and PC BM blended thin-lms. The formation of both H-and J-aggregates in the solid state have been demonstrated, and, interestingly, an energy transfer from H-aggregates or/and from residual "unstacked" molecules to J-aggregates has been found, the latter being the only emitting species. The uorescence quenching by PC BM at di erent loadings has been studied in blend lms, and it has been found particularly ecient in the case of a symmetrical peripheral substitution of the acetylene derivative core. Preliminary time-resolved measurements in emission (ns resolution) and in absorption (fs resolution) con rmed the H→J energy transfer and underlined the presence of delayed uorescence from Jaggregates, formed by energy transfer from the long-lived rst excited singlet state of H-aggregates. In all cases, a homogeneous surface morphology of thin-lms was identied by confocal uorescence microscopy.

Nanoparticles were prepared in different experimental conditions by a re-precipitation method by ... more Nanoparticles were prepared in different experimental conditions by a re-precipitation method by use of perylene and polyvinylalcohol as active material and stabilizer, respectively. The excitation and emission spectral properties of dispersions in aqueous solutions of the various samples were recorded together with the fluorescence quantum yields and lifetimes (where detectable). The experimental results are consistent with the formation of excimer-like states, responsible of the emission properties, in the nanoparticles. Confocal fluorescence and atomic force (AFM) microscopies were able to give information on the fluorescence properties and size distribution (most probable size of 3 -5 nm) of the nanoparticles.

www.rsc.org/dalton PAPER Acid-base properties of the N3 ruthenium(II) solar cell sensitizer: a co... more www.rsc.org/dalton PAPER Acid-base properties of the N3 ruthenium(II) solar cell sensitizer: a combined experimental and computational analysis † We report a combined spectro-photometric and computational investigation of the acid-base equilibria of the N3 solar cell sensitizer [Ru(dcbpyH 2 ) 2 (NCS) 2 ] (dcbpyH 2 = 4,4′-dicarboxyl-2,2′ bipyridine) in aqueous/ethanol solutions. The absorption spectra of N3 recorded at various pH values were analyzed by Single Value Decomposition techniques, followed by Global Fitting procedures, allowing us to identify four separate acid-base equilibria and their corresponding ground state pK a values. DFT/TDDFT calculations were performed for the N3 dye in solution, investigating the possible relevant species obtained by sequential deprotonation of the four dye carboxylic groups. TDDFT excited state calculations provided UV-vis absorption spectra which nicely agree with the experimental spectral shapes at various pH values. The calculated pK a values are also in good agreement with experimental data, within <1 pK a unit. Based on the calculated energy differences a tentative assignment of the N3 deprotonation pathway is reported. † Electronic supplementary information (ESI) available: Molecular orbitals energy, absorption spectra in water solution and computed pK a values. Schematic representation of the deprotonation path of N3H 4 together with the pK a values calculated by the SPH method. The structures leading to the lower pK a pathway are highlighted.

Physical Chemistry Chemical Physics, 2014

We report here a joint experimental and theoretical study of a quadrupolar, two-branched pyridini... more We report here a joint experimental and theoretical study of a quadrupolar, two-branched pyridinium derivative of interest as a potential non-linear optical material. The spectral and photophysical behaviour of this symmetric system is greatly affected by the polarity of the medium. A very efficient photoinduced intramolecular charge transfer, surprisingly more efficient than in the dipolar asymmetric analogue, is found to occur by femtosecond resolved transient absorption spectroscopy. TD-DFT calculations are in excellent agreement with these experimental findings and predict large charge displacements in the molecular orbitals describing the ground state and the lowest excited singlet state. The theoretical study also revealed that in highly polar media the symmetry of the excited state is broken giving a possible explanation to the fluorescence and transient absorption spectra resembling those of the one-branched analogous compound in the same solvents. The present study may give an important insight into the excited state deactivation mechanism of cationic (donor-p-acceptor-p-donor) + quadrupolar compounds characterised by negative solvatochromism, which are expected to show significant two-photon absorption (TPA). Moreover, the water solubility of the investigated quadrupolar system may represent an added value in view of the most promising applications of TPA materials in biology and medicine.

Journal of Physical Chemistry B, 2014

This work presents a steady-state and time-resolved UV−visible spectroscopic investigation of two... more This work presents a steady-state and time-resolved UV−visible spectroscopic investigation of two antibiotics belonging to the family of tetracyclines (doxycycline and oxytetracycline) in the micellar medium provided by p-dodecyloxybenzyltrimethylammonium bromide (pDoTABr). The spectroscopic analysis has been performed in absorption and emission with femtosecond time resolution, and at pH 5.0 and 8.7 where doxycycline and oxytetracycline are present in their neutral-zwitterionic and monoanionic forms, respectively. The experimental data have been processed by sophisticated data mining methods such as global/ target analysis and the maximum entropy method. The results unambiguously indicate that, when doxycycline and oxytetracycline are in their zwitterionic form, they are entrapped within the micelle, while when they are in their monoanionic form, they preferentially show a strong one-to-one interaction with the positively charged surfactant heads. Thus, the pH of the solution controls the inclusion of the investigated drugs into the micelle. When the drugs are entrapped inside the micelles, their spectroscopic and dynamical properties after photoexcitation change appreciably. Interestingly, the entrapped drugs are still able to strongly bind Mg 2+ cations, crucial in determining the biological functioning of tetracyclines. The femtosecond resolved measurements reveal that the drugs are efficiently pulled out of the micelles by Mg 2+ . In fact, magnesium−tetracycline complexes are detected in the aqueous phase. The present study suggests the potential promising use of ammonium surfactant micelles embedding doxycycline and oxytetracycline as "smart" drug delivery systems allowing their pH controlled inclusion and Mg 2+ induced release.