Avramopoulos, A.; Reis, H.; Tzeli, D.; Zaleśny, R.; Papadopoulos, M.G. Photoswitchable Molecular Units with Tunable Nonlinear Optical Activity: A Theoretical Investigation. Molecules2023, 28, 5646.
Avramopoulos, A.; Reis, H.; Tzeli, D.; Zaleśny, R.; Papadopoulos, M.G. Photoswitchable Molecular Units with Tunable Nonlinear Optical Activity: A Theoretical Investigation. Molecules 2023, 28, 5646.
Avramopoulos, A.; Reis, H.; Tzeli, D.; Zaleśny, R.; Papadopoulos, M.G. Photoswitchable Molecular Units with Tunable Nonlinear Optical Activity: A Theoretical Investigation. Molecules2023, 28, 5646.
Avramopoulos, A.; Reis, H.; Tzeli, D.; Zaleśny, R.; Papadopoulos, M.G. Photoswitchable Molecular Units with Tunable Nonlinear Optical Activity: A Theoretical Investigation. Molecules 2023, 28, 5646.
Abstract
A series of derivatives, involving two dithienylethene (DTE), groups, connected by several molecular linkers (bis(ethylene-1,2-dithiolato)Ni- (NiBDT), naphthalene, quasilinear oligothiophene chains) are investigated with the aid of computational quantum chemistry methods. This involves the computation of the second- and third-order nonlinear optical properties, i.e. molecular hyperpolarizabilities of the designed/selected derivatives. These properties can be efficiently controlled by DTE switches, in connection with light of appropriate frequency. We found that NiBDT, as a linker, is associated with a greater contrast, in comparison to naphthalene, between the first and second hyperpolarizabilities of the “open-open” and the “closed-closed” isomers. This is explained by invoking the low lying excited states of NiBDT. It has been found that the second hyperpolarizability can be used as an index, which follows the structural changes induced by photochromism. The two-photon absorption, which is related to the imaginary part of second hyperpolarizability, has also been investigated for the S0S1 transition. Furthermore, the intramolecular excited-state energy transfer (EET) is studied as well as the overlap between the absorption and emission spectra of the donor and acceptor groups of the molecules. The electronic coupling, VDA, between the donor and acceptor fragments, as well as the emission spectrum of the donor and the absorption spectrum of the acceptor have been computed, assuming a Förster type transfer mechanism. EET is a critical factor governing the photochromism. Two methods were used to compute VDA, one based on linear response and one based on the distributed multipole analysis (DMA); both techniques give very similar results for the dominating Coulomb contribution. For NiBDT as the linker a low VDA value has been computed. We found that VDA is affected by the molecular geometry. Our results clearly show that the linker strongly influences the communication between the open-closed DTE groups and thus, photochromism. The present computations show that full photochromism is attained in derivatives where two DTE groups are linked by a tetrathiophene chain, in agreement with experiment. The sensitivity of molecular linear and nonlinear optical properties upon photochromism can assist with the identification of the molecular isomers.
Keywords
(Hyper)polarizability; Density Functional Theory; Molecular Switches; Photochromism; Two-Photon absorption; Dithienylethene; bis(ethylene-1,2-dithiolato; Excited-state Energy Transfer
Subject
Chemistry and Materials Science, Theoretical Chemistry
Copyright:
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
