Rational classification of a series of aromatic donor–acceptor systems within the twisting intramolecular charge transfer model, a time-dependent density-functional theory investigation

Abstract

The goal of this paper is to rationalize the fluorescence activity, experimentally observed for 21 molecules of the same family as the 4-(N,N-dimethyl)anilines, based on their potential energy surfaces calculated within the twisting intramolecular charge transfer model. A classification in four groups is proposed according to the sign of two parameters, ΔEgap, characterizing the energy difference between the vertical locally and charge transfer excited states, and ΔE1S (or ΔẼ1S for pretwisted systems), representing the energy gain of the charge transfer excited state with a perpendicular conformation compared to the first vertical excited state. In this study, the time-dependent density-functional theory has been used to calculate the potential energy surfaces of the ground and excited states along the twisting angle. Computed excitation energies and optimized ground state geometries have been obtained with both B3LYP and MPW1PW91 functionals using a 6-311+G(2d,p), and a 6-31G(d) basis set, respectively. From this study, it follows that ΔEgap and ΔE1S are the main parameters necessary to understand the fluorescence activity of these molecules. The fact that the same fluorescence activity is observed for the members of each group (or subcategory for the particular case of group II), reveals the underlying twisting mechanism as a common process for all the investigated molecules, which explains their experimental dual and nondual emission.

Evidence of coupled photoinduced proton transfer and intramolecular charge transfer reaction in para-N,N-dimethylamino orthohydroxy benzaldehyde: Spectroscopic and theoretical studies

“…For the charge transfer process, the theoretical PECs for the ground and first ex- cited singlet states have been explored following the twisted intramolecular charge transfer model as proposed by Grabowski et al [22,23]. So far there are different ways of calculating the ground and excited state surfaces for the donor-acceptor CT systems [66,67]. During the evaluation of the ground state potential energy surface full geometry optimization is performed at different s (Scheme I) values ranging from À10°to 130°.…”

Photophysical properties of trans-3-(4-monomethylamino-phenyl)-acrylonitrile: Evidence of twisted intramolecular charge transfer (TICT) process

“…But the actual mechanism of CT reaction is still under controversial discussion. Many spectroscopic, thermodynamics and quantum chemical studies have been performed on photoinduced charge transfer reactions and various models are proposed to get an in depth understanding of the CT state [2][3][4][5][6][7]. The most accepted model namely twisted intramolecular charge transfer (TICT) was proposed by Grabowski et al [8].…”

Excited States from Time‐Dependent Density Functional Theory

“…69,70 In the realm of photochemistry, 71 properties of chromophores [72][73][74][75][76] and dyes [77][78][79][80][81][82][83] have been computed. For these and other systems, there is great interest in charge-transfer excitations, [84][85][86][87][88][89][90][91][92] but, as we later discuss, intermolecular charge transfer is a demanding problem for TDDFT.…”