Ch. Warns

Theory of excitonic optical line shapes of cyclic and linear hexamers: Influence of dichotomic colored noise

Abstract For Frenkel excitons moving on cyclic and linear molecular hexamers we investigate the influence of dyhamic and static disorder on their optical line shapes. The dynamic disorder describes the influence of vibrational degrees of freedom and is taken into account by fluctuations of the local excitation energy and of the transfer matrix demerit between neighbouring molecules. The fluctuations are represented by dichotomic Markov processes with colored noise. We obtain a closed set of equations of motion for the correlation functions determining the optical line shape which is solved exactly. The line shapes are discussed for various sets of model parameters as well as various arrangements of molecules and their transition dipole moments.

Influence of dichotomic colored energy fluctuations on excitonic optical line shapes of trimers and tetramers

Abstract For Frenkel excitons moving on molecular trimers and tetramers we investigate the influence of dynamic and static disorder on their optical line shapes. The dynamic disorder describes the influence of vibrational degrees of freedom and is taken into account by fluctuations of the local molecular excitation energy. The fluctuations are represented by dichotomic Markovian processes with colored noise. We obtain a closed set of equations of motion for the correlation functions determining the optical line shape which is solved exactly. The line shapes are discussed for various sets of model parameters as well as various arrangements of molecules and their transition dipole moments.

Excitonic optical line shapes of cyclic and elliptically deformed molecular aggregates with 18 units: influence of quasi-static and dynamic disorder

We investigate the influence of dynamic and static disorder on the optical line shape of Frenkel excitons moving on molecular rings, modeling bacteria photosynthetic antenna systems. The dynamic disorder, describing the influence of vibrational degrees of freedom, and the static disorder are taken into account by fluctuations of the local excitation energies of the BChl molecules. The fluctuations are represented by dichotomic Markov processes with colored noise with different amplitudes and decay constants of the correlation functions. We obtain a closed set of equations of motion for the correlation functions determining the optical line shape, which is solved numerically. We show optical line shapes of the circular aggregates with 9 and 18 BChls for different regimes of the exciton transfer under the influence of the fluctuations taking into account also a possible elliptical deformation of the ring. The line shapes are discussed for various sets of the model parameters describing static and dynamic disorders taking into account also the possible elliptical deformation of the ring. We compare our results with the experimental data.

Exciton dynamics in light harvesting systems

Abstract The optical line shape of molecular ring aggregates with 18 molecular units, modeling bacteria photo-synthetic light harvesting systems, is investigated theoretically. The molecular units are described by two-level systems with an average excitation energy e and interacting with each other through nearest-neighbor interaction. Furthermore, quasi-static and dynamic fluctuations of the local excitation energies are taken into account simulating slow motions of the protein backbone and fast molecular vibrations, respectively. The fluctuations are described by colored dichotomic Markov processes with exponentially decaying correlation functions with small (λs) and large (λ) decay constants, respectively. The optical line shape is discussed in dependence of the model parameters including a possible elliptical deformation. Furthermore we investigate the coupled coherent and incoherent energy transport in chlorosomes.

Dynamics and spectroscopy of electronic excitations in molecular aggregates

The influence of vibrational degrees of freedom on electronic excitations for a model dimer is described by a dichotomic Markov process with coloured noise. For this model the transport of the excitation between the two units of the dimer and especially the transition between coherent and incoherent motion is discussed. Furthermore the optical absorption line shape is evaluated for various values of the model parameters.

Exciton transfer in disordered molecular aggregates: Computer modeling of optical line shapes in ring bacteria antenna systems

Abstract The structure of the LH2 subunit Rps. acidophila consists of a ring of 9 αβ heterodimers with 18 B850 BChl molecules sandwiched between the α and β subunits. For Frenkel excitons moving on the ring we investigate the influence of dynamic and static disorder on their optical line shapes. The dynamic and static disorders are taken into account by fluctuations of the local energies of the BChl molecules. The fluctuations are represented by dichotomic Markov processes with coloured noise. Comparison of our theoretical results with experimental observations indicates, that the strength of the local energy fluctuation Δ should be smaller than J 2 .

Modeling excitonic line shapes of photosynthetic light harvesting systems: influence of quasi-static and dynamic disorder

Abstract The modeling of optical line shape of molecular ring aggregates with 9 and 18 molecular units of photosynthetic bacteria light-harvesting systems is investigated theoretically. The molecular units are described by two-level systems, with an average excitation energy e , which interact with each other through nearest-neighbor interaction. A possible dimerization is taken into account by allowing for alternating strong ( J S ) and weak ( J W ) transfer integrals. Furthermore, quasi-static and dynamic fluctuations of the local excitation energies are taken into account simulating slow motions of the protein backbone and fast molecular vibrations, respectively. The fluctuations are described by colored dichotomic Markov processes with exponentially decaying correlation functions with small ( λ s ) and large ( λ ) decay constants, respectively. The optical line shape is discussed with respect to the model parameters.

Cyclic molecular aggregates: influence of quasi-static and dynamic disorder on their excitonic line shapes

Abstract For Frenkel excitons moving on molecular rings modeling in part bacteria photosynthetic antenna systems we investigate the influence of static and dynamic disorders on their optical line shape. The static disorder, describing inhomogeneities and slow motions of the protein backbone and the dynamic disorder, simulating the influence of vibrational degrees of freedom, are taken into account by fluctuations of the local excitation energies of the BChI molecules. The fluctuations are represented by dichotomic Markov processes with colored noise with different amplitudes and decay constants of the correlation functions. We obtain a closed set of equations of motion for the correlation functions determining the optical line shape which is solved numerically. We display the optical line shapes of the circular aggregates with 9 BChls for different regimes of the exciton transfer under the influence of the disorders and discuss them for various sets of the model parameters describing static and dynamic disorders.

Computer simulation of excitonic optical line shapes: transfer integral fluctuations with dichotomic coloured noise

Abstract For Frenkel excitons moving on cyclic and linear molecular chains (modeling in part photosynthetic antenna systems) we investigate the influence of dynamic and static disorder on their optical line shapes. The dynamic disorder describes the influence of vibrational degrees of freedom. In our recent papers we have taken into account fluctuations of the local excitation energy. Fluctuations of the transfer matrix element between neighbouring molecules will be treated in this paper. The fluctuations are represented by dichotomic Markov processes with coloured noise. We obtain a closed set of equations of motion for the correlation functions determining the optical line shape which is solved exactly. The line shapes are discussed for various sets of the model parameters.

EXCITONIC OPTICAL LINE SHAPES OF TRIMERS AND TETRAMERS : INFLUENCE OF DICHOTOMOUS COLOURED TRANSFER INTEGRAL FLUCTUATIONS

The influence of static and dynamic disorder on the optical line shape of Frenkel excitations in trimers and tetramers is investigated. The disorder is taken into account by dichotomous stochastic processes with exponentially decaying correlation functions. For the case of fluctuating transfer integrals a closed set of equations of motion is derived for the correlation functions determining the optical line shape. The line shape is investigated for various sets of the parameters of the stochastic processes, for various arrangements of the molecules and their transition dipole moments.