Tibor Palszegi - Academia.edu (original) (raw)
Papers by Tibor Palszegi
Multiphoton and Light Driven Multielectron Processes in Organics: New Phenomena, Materials and Applications, 2000
Theoretical analysis of the ultrafast electronic-nuclear evolution of electronically excited bith... more Theoretical analysis of the ultrafast electronic-nuclear evolution of electronically excited bithiophene (2T) molecules, generalizable to longer oligothiophenes (nT) is presented. A molecular equation of motion (EOM) is derived, approximating the system of coupled Heisenberg equations of the one-electron density operators of π electrons and of the normal mode phonon (vibrational) displacement operators. The initial electronic state of the molecular evolution
Macromolecules, 1998
Trapping of migrating incoherent electronic excitation by dynamically disordered substitutional t... more Trapping of migrating incoherent electronic excitation by dynamically disordered substitutional traps in a 1-D polymer chain has been studied analyticaly and by means of Monte Carlo simulations. A closed-form analytical solution to the model is based on the assumption that the temporal changes in the spatial coordinates of the traps, due to conformational motion, can be mimicked by a global Poissonian renewal process of the polymer configuration as a whole. The excitation survival probability P(t) for this model of dynamic disorder hopping (DDH) obeys an Ornstein-Zernike-type integral equation, which can be solved analytically in the short-and long-time limits and numerically in the whole time domain. The DDH results are compared with Monte Carlo simulations using discrete and continuoustime random walks showing a good agreement. The relevance of our theoretical findings has been discussed and connections have been made to observations of migrative excitation trapping in aromatic vinyl polymers, where the trapssin the pair approximationsconsist of mobile excimer-forming sites (EFS) triggered by the local conformation of a chain.
2009 11th International Conference on Transparent Optical Networks, 2009
Transient absorption spectroscopy with femtosecond time resolution of colloidal silver nanopartic... more Transient absorption spectroscopy with femtosecond time resolution of colloidal silver nanoparticles with diameters of 10-100 nm was accomplished. The experimental study was performed by 400 nm pump-broadband probe apparatus in spectral area of 450-600 nm at 1 mJ/cm2 excitation intensity level. The obtained picosecond relaxation times depend on particle size. The revealed electron dynamics has the main responsibility for linear
Journal of Molecular Structure: THEOCHEM, 2008
The geometries of neutral 9,9′-spirobifluorene and of its single charged cation and anion are opt... more The geometries of neutral 9,9′-spirobifluorene and of its single charged cation and anion are optimized at B3LYP/6-31G∗ level of theory. Their electronic structure is described in terms of Mulliken and QTAIM (Quantum-Theory-of-Atoms-in-Molecule) population analysis. Whereas neutral and cationic species belong to D2d symmetry group, the fluorene units in their anionic counterpart are non-equivalent (C2v symmetry group) due to Jahn–Teller effect.
physica status solidi (b), 1998
Laser Physics, 2009
Time-resolved femtosecond multicolor absorption spectroscopy of silver nanoparticle (NP) colloids... more Time-resolved femtosecond multicolor absorption spectroscopy of silver nanoparticle (NP) colloids with particle diameter in range of 10–30 nm is presented. The amplified femtosecond excitation of the surface plasmon resonance band resulted in transient absorption spectra reflecting the electron-phonon relaxation dynamics, which takes place on the early picosecond time scale. The monitored band with enhanced absorption in the 490–540 nm spectral
Langmuir, 2009
Solvation is an important phenomenon, especially in association with heterogeneous phase interact... more Solvation is an important phenomenon, especially in association with heterogeneous phase interactions. Coumarin C522, C(14)H(12)NO(2)F(3), is used as a fluorophore probe to study the interaction between coumarin and a reduced-charge montmorillonite (RCM) surface. Such hydrophilic and hydrophobic interactions are of interest for sorption processes in confined environments. The prepared RCM series with 0.00, 0.12, 0.26, 0.43, 0.66, and 0.97 Li(+) molar fractions provide different surface charges. The aqueous dispersion of the C522/water/RCM system is studied by using steady-state and time-resolved fluorescence spectroscopies. Both the Stokes shift and the dynamics of the solvation process varied as a function of surface charge. Steady-state fluorescence spectroscopy reveals that the C522 Stokes shift varies from 5,115 cm(-1) for the 0.00 Li(+) molar fraction to 3,988 cm(-1) for the 0.97 Li(+) molar fraction. Time-resolved fluorescence spectroscopy determines that the decay time T((1)) varies from 1.0 ps for the 0.00 Li(+) molar fraction to 3.6 ps for the 0.97 Li(+) molar fraction. Within the range of a few picoseconds, the dynamics of the water solvation shell may be described with H-bond rearrangement, modified with the different RCM surface charges. Two models illustrating the interactions between C522 and RCM in water are proposed which qualitatively describe the dynamics. To the best of our knowledge, this experiment is the first measurement of solvation dynamics on a montmorillonite structure surface using ultrafast laser fluorescence spectroscopy.
Journal of Luminescence, 1997
Abstract Trapping of migrating incoherent electronic excitation in dynamically disordered systems... more Abstract Trapping of migrating incoherent electronic excitation in dynamically disordered systems has been studied by the dynamic disorder hopping (DDH) method. The central point is the calculation of the DDH averaged number of visited sites 〈 S ( t )〉 which determines the donor excitation survival probability 〈 P D ( t )〉. The method presented is applied to migrative excitation trapping (MET) (i) along a vinyl chain of chromophores and (ii) in polymer fractals.
The Journal of Chemical Physics, 2000
ABSTRACT
The Journal of Chemical Physics, 1996
Electronic excitations along sites that undergo spatial and temporal fluctuations due to conforma... more Electronic excitations along sites that undergo spatial and temporal fluctuations due to conformational chain motion have been studied in the picture of the stochastic master equation by means of the dynamic Monte Carlo (DMC) and the cumulant expansion (CE) approach. An incoherent site‐to‐site hopping which is adiabatic relative to the changes of conformational site coordinates has been assumed. The elementary act of conformational change has been considered to be fast, whereas the electronic transfer during the time period of the conformational event has been assumed to be negligibly small. The time evolution of electronic intersite coupling is thus controlled by chromophore sites that, in particular, correspond to the conformational minima of the potential energy landscape. The generalized equations of motion adapted for both the DMC and the CE analysis have been reduced to formulate donor site excitation probabilities 〈Piexc(t)〉 and donor excitation survival functions 〈PD(t)〉 for a simplified chain. In...
The Journal of Chemical Physics, 2006
We study the information content of two-dimensional (2D) electronic photon-echo (PE) spectra, wit... more We study the information content of two-dimensional (2D) electronic photon-echo (PE) spectra, with special emphasis on their potential to distinguish, for waiting times T=0, between different conformations of electronically coupled symmetric dimers. The analysis is performed on the basis of an analytical formula for the frequency-domain 2D PE signal. The symmetric dimers are modeled in terms of two identical, energy-degenerate, excitonically coupled pairs of electronic states in the site representation. The spectra of conformationally weighted ensembles, composed of either two or four dimers, are compared with their one-dimensional linear absorption counterparts. In order to provide a realistic coupling pattern for the ensemble consisting of four dimers, excitonic couplings are estimated on the basis of optimized geometries and site-transition dipole moments, calculated by standard semiempirical methods for the bridged bithiophene structure 1,2-bithiophene-2-yl-ethane-1,2-dion (T2[CO]2). In the framework of our model, the highly readable 2D PE spectra can unambiguously identify spectral doublets, by relating peak heights and positions with mutual orientations of site-localized transition dipoles.
The Journal of Chemical Physics, 1998
Incoherent electronic excitation transport (EET) along chromophore-sites has been studied in the ... more Incoherent electronic excitation transport (EET) along chromophore-sites has been studied in the presence of conformational and librational motion by using a rotor chain model as the mobile vehicle. The time-evolution of the electronic site excitation probability vector Pexc(t) averaged by conformational-librational dynamic disorder has been calculated by a second-order cumulant expansion (CE) approach. A master equation for conformer distributions in torsional space has been used [G. J. Moro, J. Chem. Phys. 94, 8577 (1991) and J. Chem. Phys. 97, 5749 (1992)] to describe the coupled, motional stochastic dynamics of a rotor chain. Based upon this model, the correlation functions of excitation transfer rates, important for the calculation of the second cumulants of the stochastic excitation transfer rate matrices, have been constructed. A simplified procedure for evaluating the correlation functions for the L steep minima of torsional angle-dependent symmetrical potentials of nearest-neighbor rotor-pairs an...
The Journal of Chemical Physics, 2002
The two-dimensional (2D) temporal shape of the (degenerate) three-pulse photon-echo (3-PPE) polar... more The two-dimensional (2D) temporal shape of the (degenerate) three-pulse photon-echo (3-PPE) polarization P(3)(t′,Τ12,Τ23=0) has been theoretically analyzed for a weakly interacting two-site system (TSS) in the presence of site inhomogeneous broadening. The TSS has been modeled in terms of two identical, energy-degenerate, excitonically coupled pairs of electronic states in the site-representation (i.e., two S0 and S1 states forming a 4-level system). The 2D time-domain signal S(t′,Τ12,Τ23=0) has been derived in a closed-form solution which allowed to formulate the analytical Fourier transform analog under sequential δ-pulse excitation. The resulting 2D PE signal in frequency–frequency space S(ωt′,ωΤ12) is formed in the region of the resonant, optical carrier frequency by, generally, four peaks, arranged at the edges of a square with distances determined by the excitonic coupling. The two diagonal peaks are of one-exciton origin, while the two off-diagonal (cross) peaks involve two-exciton effects, too. The relative heights of the four peaks are in distinct relation with the mutual orientation of the site-localized transition dipoles, thus these 2D line shapes serving as a structural probe for resonantly interacting molecules. The shapes of the peaks reflect the ratio between homogeneous and inhomogeneous dephasings and can be used for structural studies of statically disordered systems of TSS. The semiclassical two-site model is intended to provide a preparatory platform for mimicking electronically coupled segmental pairs dispersed in energy and space along the strongly disordered main chain contour. The results of the model calculation are taken to discuss the potential and the limitations of 2D line shape echo-spectroscopy in the study of short-range coherences and electronic coupling in π-conjugated polymers.
Chemical Physics, 1994
The approach of the effective medium approximation (EMA) has been used for the description of inc... more The approach of the effective medium approximation (EMA) has been used for the description of incoherent migration of electronic excitation. The migration takes plsce among the chmmophores linked iato a polymer chain which is in amformational motion. The polynomial equation, corresponding to two relative positions of neighbouring chmmophores, yields the hypersurface of the effective rate coefficients Wdz) of the migratian, where z is the pammeter of the Laplace transformation. The inverse Laplace transformation of functions of W&z) gives the mesn-squsrc distance and the diffusion coefficient o(t) of the migration of excitation. The dependetke of o(t) as well as of its limit value for long time D(~0) on the rste of the trsns # gauche (T # G) conformational motion has been outlined for the polyvinylnaphtbalene (PVN) &sin.
Chemical Physics, 1996
An effective medium approximation (EMA) has been used in an attempt to analyze incoherent migrati... more An effective medium approximation (EMA) has been used in an attempt to analyze incoherent migrational trapping in a system of I-D regular and immobile donors, where trapping is a time-dependent stochastic process-due to the dynamic conformational disorder of interstitial acceptors. By assuming (I) the time duration of the elementary act of conformational transition to be longer than the time involved in the electronic site-to-site transfer and (II) the transport of excitation during conformational event to be negligible, the hypersurface of the effective trapping rate coefficient Ken(z) in Laplace space can be formulated on the basis of a stochastic master equation analysis. The computation has been centered on conformational transitions between two relative positions in the donor-acceptor pair connected by flexible carbon-carbon spacer-groups, where the dynamical fluctuation of acceptor positions, due to the conformational motion of spacer segments, dichotomically modulates the trapping rate coefficient. On these premises Ken(z) can be obtained by numerically solving a third order polynomial equation which allows, after Laplace inversion, the mean-square distance of migrating excitation (r2(t)) and the survival probability of donor excitation (P(t)) to be analyzed. The effect of conformational motion on the excitation trapping efficiency has been calculated for a series of conformative and electronic parameters. The non-Markovian character of trapping becomes apparent for slow to moderate conformational motion in the short-to-intermediate time regime and disappears for fast conformational transitions. Furthermore, the asymptotic trapping rate K~n(z = 0 +) which represents the Markov approximation of the memory function Ken(t) has been analyzed for different rates of conformational motion and equilibrium conformational probabilities and, finally, the investigation has been extended to 2-D transport in a preliminary attempt.
The Journal of Physical Chemistry A, 2006
The linear absorption and fluorescence spectra as well as the oscillator strengths of 2,2&... more The linear absorption and fluorescence spectra as well as the oscillator strengths of 2,2',7,7'-tetraphenyl-9,9'-spirobifluorene (A), 2,2',7,7'-tetrakis(biphenyl-4-yl)-9,9'-spirobifluorene (B), and 2,2',7,7'-tetrakis(9,9'-spirobifluoren-2-yl)-9,9'-spirobifluorene (C) are calculated on the basis of the collective electronic oscillator (CEO) approach of Mukamel et al. (see, e.g., Chem. Rev. 2002, 102, 3171). The graphical visualization and quantitative characterization of CEO modes allows one to extract the real-space distribution of electronic excitations of the molecules under study. Effects of the lengthening and branching of the oligophenylene segments have been analyzed. The influence of the lowest excited (S1) vs ground-state (S0) geometry changes on the CEO modes is investigated and related to the geometry changes of the molecular parts. The obtained theoretical results are in good agreement with experimental trends observed in absorption and fluorescence data.
Journal of Photochemistry and Photobiology A: Chemistry, 2017
Femtochemistry and Femtobiology - Ultrafast Dynamics in Molecular Science - With Foreword by Prof A H Zewail, Nobel Laureate in Chemistry, 1999, 2002
Multiphoton and Light Driven Multielectron Processes in Organics: New Phenomena, Materials and Applications, 2000
Theoretical analysis of the ultrafast electronic-nuclear evolution of electronically excited bith... more Theoretical analysis of the ultrafast electronic-nuclear evolution of electronically excited bithiophene (2T) molecules, generalizable to longer oligothiophenes (nT) is presented. A molecular equation of motion (EOM) is derived, approximating the system of coupled Heisenberg equations of the one-electron density operators of π electrons and of the normal mode phonon (vibrational) displacement operators. The initial electronic state of the molecular evolution
Macromolecules, 1998
Trapping of migrating incoherent electronic excitation by dynamically disordered substitutional t... more Trapping of migrating incoherent electronic excitation by dynamically disordered substitutional traps in a 1-D polymer chain has been studied analyticaly and by means of Monte Carlo simulations. A closed-form analytical solution to the model is based on the assumption that the temporal changes in the spatial coordinates of the traps, due to conformational motion, can be mimicked by a global Poissonian renewal process of the polymer configuration as a whole. The excitation survival probability P(t) for this model of dynamic disorder hopping (DDH) obeys an Ornstein-Zernike-type integral equation, which can be solved analytically in the short-and long-time limits and numerically in the whole time domain. The DDH results are compared with Monte Carlo simulations using discrete and continuoustime random walks showing a good agreement. The relevance of our theoretical findings has been discussed and connections have been made to observations of migrative excitation trapping in aromatic vinyl polymers, where the trapssin the pair approximationsconsist of mobile excimer-forming sites (EFS) triggered by the local conformation of a chain.
2009 11th International Conference on Transparent Optical Networks, 2009
Transient absorption spectroscopy with femtosecond time resolution of colloidal silver nanopartic... more Transient absorption spectroscopy with femtosecond time resolution of colloidal silver nanoparticles with diameters of 10-100 nm was accomplished. The experimental study was performed by 400 nm pump-broadband probe apparatus in spectral area of 450-600 nm at 1 mJ/cm2 excitation intensity level. The obtained picosecond relaxation times depend on particle size. The revealed electron dynamics has the main responsibility for linear
Journal of Molecular Structure: THEOCHEM, 2008
The geometries of neutral 9,9′-spirobifluorene and of its single charged cation and anion are opt... more The geometries of neutral 9,9′-spirobifluorene and of its single charged cation and anion are optimized at B3LYP/6-31G∗ level of theory. Their electronic structure is described in terms of Mulliken and QTAIM (Quantum-Theory-of-Atoms-in-Molecule) population analysis. Whereas neutral and cationic species belong to D2d symmetry group, the fluorene units in their anionic counterpart are non-equivalent (C2v symmetry group) due to Jahn–Teller effect.
physica status solidi (b), 1998
Laser Physics, 2009
Time-resolved femtosecond multicolor absorption spectroscopy of silver nanoparticle (NP) colloids... more Time-resolved femtosecond multicolor absorption spectroscopy of silver nanoparticle (NP) colloids with particle diameter in range of 10–30 nm is presented. The amplified femtosecond excitation of the surface plasmon resonance band resulted in transient absorption spectra reflecting the electron-phonon relaxation dynamics, which takes place on the early picosecond time scale. The monitored band with enhanced absorption in the 490–540 nm spectral
Langmuir, 2009
Solvation is an important phenomenon, especially in association with heterogeneous phase interact... more Solvation is an important phenomenon, especially in association with heterogeneous phase interactions. Coumarin C522, C(14)H(12)NO(2)F(3), is used as a fluorophore probe to study the interaction between coumarin and a reduced-charge montmorillonite (RCM) surface. Such hydrophilic and hydrophobic interactions are of interest for sorption processes in confined environments. The prepared RCM series with 0.00, 0.12, 0.26, 0.43, 0.66, and 0.97 Li(+) molar fractions provide different surface charges. The aqueous dispersion of the C522/water/RCM system is studied by using steady-state and time-resolved fluorescence spectroscopies. Both the Stokes shift and the dynamics of the solvation process varied as a function of surface charge. Steady-state fluorescence spectroscopy reveals that the C522 Stokes shift varies from 5,115 cm(-1) for the 0.00 Li(+) molar fraction to 3,988 cm(-1) for the 0.97 Li(+) molar fraction. Time-resolved fluorescence spectroscopy determines that the decay time T((1)) varies from 1.0 ps for the 0.00 Li(+) molar fraction to 3.6 ps for the 0.97 Li(+) molar fraction. Within the range of a few picoseconds, the dynamics of the water solvation shell may be described with H-bond rearrangement, modified with the different RCM surface charges. Two models illustrating the interactions between C522 and RCM in water are proposed which qualitatively describe the dynamics. To the best of our knowledge, this experiment is the first measurement of solvation dynamics on a montmorillonite structure surface using ultrafast laser fluorescence spectroscopy.
Journal of Luminescence, 1997
Abstract Trapping of migrating incoherent electronic excitation in dynamically disordered systems... more Abstract Trapping of migrating incoherent electronic excitation in dynamically disordered systems has been studied by the dynamic disorder hopping (DDH) method. The central point is the calculation of the DDH averaged number of visited sites 〈 S ( t )〉 which determines the donor excitation survival probability 〈 P D ( t )〉. The method presented is applied to migrative excitation trapping (MET) (i) along a vinyl chain of chromophores and (ii) in polymer fractals.
The Journal of Chemical Physics, 2000
ABSTRACT
The Journal of Chemical Physics, 1996
Electronic excitations along sites that undergo spatial and temporal fluctuations due to conforma... more Electronic excitations along sites that undergo spatial and temporal fluctuations due to conformational chain motion have been studied in the picture of the stochastic master equation by means of the dynamic Monte Carlo (DMC) and the cumulant expansion (CE) approach. An incoherent site‐to‐site hopping which is adiabatic relative to the changes of conformational site coordinates has been assumed. The elementary act of conformational change has been considered to be fast, whereas the electronic transfer during the time period of the conformational event has been assumed to be negligibly small. The time evolution of electronic intersite coupling is thus controlled by chromophore sites that, in particular, correspond to the conformational minima of the potential energy landscape. The generalized equations of motion adapted for both the DMC and the CE analysis have been reduced to formulate donor site excitation probabilities 〈Piexc(t)〉 and donor excitation survival functions 〈PD(t)〉 for a simplified chain. In...
The Journal of Chemical Physics, 2006
We study the information content of two-dimensional (2D) electronic photon-echo (PE) spectra, wit... more We study the information content of two-dimensional (2D) electronic photon-echo (PE) spectra, with special emphasis on their potential to distinguish, for waiting times T=0, between different conformations of electronically coupled symmetric dimers. The analysis is performed on the basis of an analytical formula for the frequency-domain 2D PE signal. The symmetric dimers are modeled in terms of two identical, energy-degenerate, excitonically coupled pairs of electronic states in the site representation. The spectra of conformationally weighted ensembles, composed of either two or four dimers, are compared with their one-dimensional linear absorption counterparts. In order to provide a realistic coupling pattern for the ensemble consisting of four dimers, excitonic couplings are estimated on the basis of optimized geometries and site-transition dipole moments, calculated by standard semiempirical methods for the bridged bithiophene structure 1,2-bithiophene-2-yl-ethane-1,2-dion (T2[CO]2). In the framework of our model, the highly readable 2D PE spectra can unambiguously identify spectral doublets, by relating peak heights and positions with mutual orientations of site-localized transition dipoles.
The Journal of Chemical Physics, 1998
Incoherent electronic excitation transport (EET) along chromophore-sites has been studied in the ... more Incoherent electronic excitation transport (EET) along chromophore-sites has been studied in the presence of conformational and librational motion by using a rotor chain model as the mobile vehicle. The time-evolution of the electronic site excitation probability vector Pexc(t) averaged by conformational-librational dynamic disorder has been calculated by a second-order cumulant expansion (CE) approach. A master equation for conformer distributions in torsional space has been used [G. J. Moro, J. Chem. Phys. 94, 8577 (1991) and J. Chem. Phys. 97, 5749 (1992)] to describe the coupled, motional stochastic dynamics of a rotor chain. Based upon this model, the correlation functions of excitation transfer rates, important for the calculation of the second cumulants of the stochastic excitation transfer rate matrices, have been constructed. A simplified procedure for evaluating the correlation functions for the L steep minima of torsional angle-dependent symmetrical potentials of nearest-neighbor rotor-pairs an...
The Journal of Chemical Physics, 2002
The two-dimensional (2D) temporal shape of the (degenerate) three-pulse photon-echo (3-PPE) polar... more The two-dimensional (2D) temporal shape of the (degenerate) three-pulse photon-echo (3-PPE) polarization P(3)(t′,Τ12,Τ23=0) has been theoretically analyzed for a weakly interacting two-site system (TSS) in the presence of site inhomogeneous broadening. The TSS has been modeled in terms of two identical, energy-degenerate, excitonically coupled pairs of electronic states in the site-representation (i.e., two S0 and S1 states forming a 4-level system). The 2D time-domain signal S(t′,Τ12,Τ23=0) has been derived in a closed-form solution which allowed to formulate the analytical Fourier transform analog under sequential δ-pulse excitation. The resulting 2D PE signal in frequency–frequency space S(ωt′,ωΤ12) is formed in the region of the resonant, optical carrier frequency by, generally, four peaks, arranged at the edges of a square with distances determined by the excitonic coupling. The two diagonal peaks are of one-exciton origin, while the two off-diagonal (cross) peaks involve two-exciton effects, too. The relative heights of the four peaks are in distinct relation with the mutual orientation of the site-localized transition dipoles, thus these 2D line shapes serving as a structural probe for resonantly interacting molecules. The shapes of the peaks reflect the ratio between homogeneous and inhomogeneous dephasings and can be used for structural studies of statically disordered systems of TSS. The semiclassical two-site model is intended to provide a preparatory platform for mimicking electronically coupled segmental pairs dispersed in energy and space along the strongly disordered main chain contour. The results of the model calculation are taken to discuss the potential and the limitations of 2D line shape echo-spectroscopy in the study of short-range coherences and electronic coupling in π-conjugated polymers.
Chemical Physics, 1994
The approach of the effective medium approximation (EMA) has been used for the description of inc... more The approach of the effective medium approximation (EMA) has been used for the description of incoherent migration of electronic excitation. The migration takes plsce among the chmmophores linked iato a polymer chain which is in amformational motion. The polynomial equation, corresponding to two relative positions of neighbouring chmmophores, yields the hypersurface of the effective rate coefficients Wdz) of the migratian, where z is the pammeter of the Laplace transformation. The inverse Laplace transformation of functions of W&z) gives the mesn-squsrc distance and the diffusion coefficient o(t) of the migration of excitation. The dependetke of o(t) as well as of its limit value for long time D(~0) on the rste of the trsns # gauche (T # G) conformational motion has been outlined for the polyvinylnaphtbalene (PVN) &sin.
Chemical Physics, 1996
An effective medium approximation (EMA) has been used in an attempt to analyze incoherent migrati... more An effective medium approximation (EMA) has been used in an attempt to analyze incoherent migrational trapping in a system of I-D regular and immobile donors, where trapping is a time-dependent stochastic process-due to the dynamic conformational disorder of interstitial acceptors. By assuming (I) the time duration of the elementary act of conformational transition to be longer than the time involved in the electronic site-to-site transfer and (II) the transport of excitation during conformational event to be negligible, the hypersurface of the effective trapping rate coefficient Ken(z) in Laplace space can be formulated on the basis of a stochastic master equation analysis. The computation has been centered on conformational transitions between two relative positions in the donor-acceptor pair connected by flexible carbon-carbon spacer-groups, where the dynamical fluctuation of acceptor positions, due to the conformational motion of spacer segments, dichotomically modulates the trapping rate coefficient. On these premises Ken(z) can be obtained by numerically solving a third order polynomial equation which allows, after Laplace inversion, the mean-square distance of migrating excitation (r2(t)) and the survival probability of donor excitation (P(t)) to be analyzed. The effect of conformational motion on the excitation trapping efficiency has been calculated for a series of conformative and electronic parameters. The non-Markovian character of trapping becomes apparent for slow to moderate conformational motion in the short-to-intermediate time regime and disappears for fast conformational transitions. Furthermore, the asymptotic trapping rate K~n(z = 0 +) which represents the Markov approximation of the memory function Ken(t) has been analyzed for different rates of conformational motion and equilibrium conformational probabilities and, finally, the investigation has been extended to 2-D transport in a preliminary attempt.
The Journal of Physical Chemistry A, 2006
The linear absorption and fluorescence spectra as well as the oscillator strengths of 2,2&... more The linear absorption and fluorescence spectra as well as the oscillator strengths of 2,2',7,7'-tetraphenyl-9,9'-spirobifluorene (A), 2,2',7,7'-tetrakis(biphenyl-4-yl)-9,9'-spirobifluorene (B), and 2,2',7,7'-tetrakis(9,9'-spirobifluoren-2-yl)-9,9'-spirobifluorene (C) are calculated on the basis of the collective electronic oscillator (CEO) approach of Mukamel et al. (see, e.g., Chem. Rev. 2002, 102, 3171). The graphical visualization and quantitative characterization of CEO modes allows one to extract the real-space distribution of electronic excitations of the molecules under study. Effects of the lengthening and branching of the oligophenylene segments have been analyzed. The influence of the lowest excited (S1) vs ground-state (S0) geometry changes on the CEO modes is investigated and related to the geometry changes of the molecular parts. The obtained theoretical results are in good agreement with experimental trends observed in absorption and fluorescence data.
Journal of Photochemistry and Photobiology A: Chemistry, 2017
Femtochemistry and Femtobiology - Ultrafast Dynamics in Molecular Science - With Foreword by Prof A H Zewail, Nobel Laureate in Chemistry, 1999, 2002