DFT studies on solvent dependence of electronic absorption spectra of free-base and protonated porphyrin (original) (raw)
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Excited states absorption spectra of porphyrins – Solvent effects
Chemical Physics Letters, 2013
We propose a combination of different techniques to obtain the absorption cross-section spectra of triplet-and singlet-states in porphyrin-like molecules. Two extensions of the Z-scan technique are employed (pulse train Z-scan and white-light Z-scan) together with absorbance spectroscopy and laser flash photolysis. This approach allowed us to investigate features of excited-states absorption of meso-tetrakis (methylpyridiniumyl) porphyrin (TMPyP) that revealed the influence of solvents on the vibronic structuration of the transitions assigned to triplet-states, probably caused by hydrogen bonds established between the porphyrin and solvent molecules.
Solvent effect on the nonlinear absorption of 5,10-A2B2meso substituted porphyrins
Photochemical & Photobiological Sciences, 2013
The effect of the solvent on the nonlinear absorptive properties of two series of 5,10-A 2 B 2 porphyrins was investigated with an open Z-scan technique in ns time regime. The recorded responses, which varied between compounds and solvents, were fitted with a four-level model where one-photon excited state absorption is followed by a two-photon process arising from the higher excited states. For most of the compounds the positive nonlinear absorption was stronger in toluene than in DMF and chloroform. This 10 was attributed to enhanced two-photon absorption in toluene. For DMF and chloroform the solvent effects were most likely compound specific. It was demonstrated that high saturation intensity of two-photon absorption shifts the RSA/SA turnover into higher fluence range, which is desirable for optical limiting applications. This saturation intensity of two-photon absorption varied between compounds and solvents. Additionally, nonlinear scattering contributed strongly to the open Z-scan responses for many compounds 15 in chlorobenzene and chloroform/chlorobenzene solutions. This was associated with the photodegradation of chlorobenzene. 65 NLA. Taking this into account the choice of a chemical environment which minimizes aggregation is crucial.
Journal of Molecular Modeling, 2019
Electronic and spectroscopic properties of tetracationic 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphyrin (TMPyP) were investigated in the framework of the density functional theory (DFT). Modeling of implicit solvent, charge effects, and medium acidity were performed and compared with experimental results. Various hybrid exchange correlation functionals in the Kohn-Sham Scheme of the DFT were employed and various porphyrin models were constructed, simulating different environmental conditions. Since porphyrins present several technological applications with a plethora of interacting systems and the optical spectra profiles are often used to characterize these macrocyclic compounds, the study performed here aims to stablish a correct description of the UV-Vis spectrum. These results allowed to reproduce, both qualitatively as well as quantitatively, the Soret band of the TMPyP.
Journal of Luminescence, 2013
Steady state and time-resolved fluorescence properties of porphyrin appended 1,3,4-oxadiazoles and thiazoles were described in homogeneous medium as well as in presence of cationic surfactant cetyltrimethylammonium bromide (CTAB). The electron withdrawing substituent on the porphyrin moiety in both the cases make a donor-spacer-acceptor type of intramolecular photoinduced electron transfer (PET) system resulting substantial quenching in porphyrin fluorescence due to partial energy migration towards the acceptor in the excited state. The increase in fluorescence yield as well as appreciable difference in fluorescence decay behavior in aqueous buffer solution of pH 4.2 from that in chloroform solution is believed due to partial protonation of the porphyrin ring. All the investigated systems show preferential binding into the interfacial region of the micellar sub-domain with varying degree of penetration depending on the nature of the substituent. Almost 2-4 fold increase in fluorescence yield for the probes is explained on the basis of restricted flexibility and corresponding decrease in total nonradiative rate inside the micellar interface layer.
Excited-state properties of water-soluble porphyrin dimers
Chemical Physics Letters, 1986
The excited-state properties of heterodimers of tetra(Ccarboxyphenyl)porphyrin (TPPC) and tetra(N-methylpyridyl)porphyrin (TMPyP) are studied by absorption and emission spectroscopy, EPR and zero-field ODMR. The excited singlet and triplet states of dimers formed by pairing HzTPPC with HzTMPyP or ZnTMPyP are localized on H?TPPC. The dimers formed by pairing H,TPPC with CuTMPyP and H,TMPyP with ZnTPPC or CuTPPC are non-fluorescent due to intramolecular electron transfer.
Probing the Interactions of Porphyrins with Macromolecules Using NMR Spectroscopy Techniques
Molecules, 2021
Porphyrinic compounds are widespread in nature and play key roles in biological processes such as oxygen transport in blood, enzymatic redox reactions or photosynthesis. In addition, both naturally derived as well as synthetic porphyrinic compounds are extensively explored for biomedical and technical applications such as photodynamic therapy (PDT) or photovoltaic systems, respectively. Their unique electronic structures and photophysical properties make this class of compounds so interesting for the multiple functions encountered. It is therefore not surprising that optical methods are typically the prevalent analytical tool applied in characterization and processes involving porphyrinic compounds. However, a wealth of complementary information can be obtained from NMR spectroscopic techniques. Based on the advantage of providing structural and dynamic information with atomic resolution simultaneously, NMR spectroscopy is a powerful method for studying molecular interactions betwee...
Research on Chemical Intermediates, 2015
Susceptibility to interact with trifluoroacetic acid (TFA) of selected freebase porphyrins, including a novel lipophilic 3-n-pentadecyl(phenoxy)-ethoxyphenyl-substituted porphyrin, and photostability of their diprotonated compounds was explored in benzene and N,N-dimethylformamide (DMF). Results have been discussed in terms of the commonly applied pK a-based procedure and confronted with a simple approach derived from experimentally-determined correlations reflecting the porphyrins affinity for TFA. Density functional theory (DFT) has proved the porphyrin moiety creates stable diprotonated species involving two TFA molecules, in which the fluorine atoms effectively contribute to the overall interaction of the acid with the porphyrin macrocycle. The relevance of the mesosubstituent and ambient medium to the reactivity and photostability of diverse porphyrin derivatives was emphasized and referred to structural features of the investigated diprotonated porphyrins.
The solvent dependence of the photophysical properties of meso-tetra(aryl)porphyrins with electron-donating and electron withdrawing meso substituents and their dications with CF 3 COOH and CH 2 ClCOOH has been studied. Dependence of the natural radiative lifetimes (t 1 , t 2, t 3), non-radiative rate constant (k nr), fluorescence quantum yields (F f), stokes shifts and the intensity of the emission bands of the free base porphyrins and the dications on the solvent polarity and Lorentz-Lorenz function, F(n 2) = (n 2-l)/(n 2 + 2) (n, refractive index) was investigated in details. Furthermore, the degree of configuration interaction (CI) between the excited states was evaluated from the f Soret /f Q(0,0) ratio. It was found that the optical absorption and fluorescence characteristics of the free base porphyrins and their diacids can be finely tuned by changing the solvent's polarity, even though no close correlation was observed between some of the optical properties and the solvent properties.
Semiempirical and spectroscopic study of a novel porphyrin dyad
International Journal of Quantum Chemistry, 2001
Semiempirical calculations and ultraviolet-visible experiments have been carried out on a novel bisporphyrin system. The present work reveals that an oligothiophene ethynyl-linked spacer promotes high electronic interactions over a large distance in this dyad.