Dynamics of Excitons in Conjugated Molecules and Organic Semiconductor Systems

Abstract

The exciton, an excited electron–hole pair bound by Coulomb attraction, plays a key role in photophysics of organic molecules and drives practically important phenomena such as photoinduced mechanical motions of a molecule, photochemical conversions, energy transfer, generation of free charge carriers, etc. Its behavior in extended π-conjugated molecules and disordered organic films is very different and very rich compared with exciton behavior in inorganic semiconductor crystals. Due to the high degree of variability of organic systems themselves, the exciton not only exerts changes on molecules that carry it but undergoes its own changes during all phases of its lifetime, that is, birth, conversion and transport, and decay. The goal of this review is to give a systematic and comprehensive view on exciton behavior in π-conjugated molecules and molecular assemblies at all phases of exciton evolution with emphasis on rates typical for this dynamic picture and various consequences of the above dynamics. To uncover the rich variety of exciton behavior, details of exciton formation, exciton transport, exciton energy conversion, direct and reverse intersystem crossing, and radiative and nonradiative decay are considered in different systems, where these processes lead to or are influenced by static and dynamic disorder, charge distribution symmetry breaking, photoinduced reactions, electron and proton transfer, structural rearrangements, exciton coupling with vibrations and intermediate particles, and exciton dissociation and annihilation as well.

One-Pot Synthesis of Pyreno[2,1-b]furan Molecules with Two-Photon Absorption Properties

“…Pure organic π-conjugated luminescence molecules have attracted intense interest because of their practical applications in the fields of organic electronics, nonlinear optics, energy storage devices, , and bioimaging. , In recent years, much effort has been devoted to the construction of multifunctional organic luminescence materials with blue/green/red (RGB) emission. Moreover, organic fluorophores with two-photon absorption (TPA) properties exhibit unique advantages for cell imaging, biomedical diagnosis, and therapy because of their long excitation wavelengths, less photobleaching, higher three-dimensional (3D) resolution, and penetration depths .…”

Intersystem Crossing in Acceptor–Donor–Acceptor Type Organic Photovoltaic Molecules Promoted by Symmetry Breaking in Polar Environments

“…The recombination dynamics in the A-D-A molecules may be altered by the effect in the excited-state energy landscape induced by the polar environment . In the studied molecules, the stabilized S 1 * states undergo the process of ISC, resulting in forming triplet states (T 1 ) on a longer time scale (>20 ps).…”

“…The vertical transition S 1 state is symmetric with a pure quadrupole where the electronic excitation distributes evenly over the two A-D branches. The polar solvation effect induces symmetry breaking during vibrational relaxation, − , resulting in the excitation partially localized on one A-D branch (Figure S8). Therefore, the relaxed S 1 * state possesses CT character with a non-zero dipole (Table S3) which is stabilized by interacting with the polar environment. ,,, The computational values may vary from the exact energies in solvents due to our assumption of the implicit solvation model. , Higher-level quantum chemical calculation methods − considering the explicit solvent molecules may be necessary for a more accurate description of the interaction between the molecule and surroundings.…”

“…The polar solvation effect induces symmetry breaking during vibrational relaxation, − , resulting in the excitation partially localized on one A-D branch (Figure S8). Therefore, the relaxed S 1 * state possesses CT character with a non-zero dipole (Table S3) which is stabilized by interacting with the polar environment. ,,, The computational values may vary from the exact energies in solvents due to our assumption of the implicit solvation model. , Higher-level quantum chemical calculation methods − considering the explicit solvent molecules may be necessary for a more accurate description of the interaction between the molecule and surroundings. Nonetheless, the trend predicted by the quantum chemical calculation is instructive for qualitatively understanding the effect of polar environments on excited-state dynamics.…”

“…The vertical transition S 1 state is symmetric with a pure quadrupole where the electronic excitation distributes evenly over the two A-D branches. The polar solvation effect induces symmetry breaking during vibrational relaxation, [26][27][28][29]39 resulting in the excitation partially localized on one A-D branch (Figure S8). 39 Therefore, the relaxed S 1 * state possesses CT character with a non-zero dipole (Table S3) which is stabilized by interacting with the polar environment.…”