Issue 32, 2021

The mechanism behind the photochromism and photomagnetism of type II biindenylidenediones: multiconfigurational, perturbative and density functional theory studies

Abstract

Biindenylidenediones (BIDs) are a family of compounds that have been studied for a relatively short time. The crystals of these compounds are yellowish, and become purplish when they are irradiated and return back to their original color slowly in the dark or quickly when they are heated up. BIDs can be classified into different subfamilies depending on the nature of their substituents. BID-II crystals show a thermally dependent electron paramagnetic resonance (EPR) signal that is a characteristic of chemical species with unpaired electrons. These properties make BIDs very attractive for industrial applications but the mechanisms responsible for their photochromism and photomagnetism are still under debate. In this article, a computational study focused on the BID-II subfamily is presented. A variety of multiconfigurational methods (CASSCF, CASPT2 and IDDCI) have been used to study exhaustively the topography of the potential energy surfaces of the lower electronic states of a single BID molecule. Methods based on density functional theory (DFT) were then used to model the most important structures in a periodic crystal system. Our results suggest that δ-hydrogen abstraction could explain the observed experimental phenomena. After the initial excitation to the 1ππ* state, non-symmetric nπ* minima are populated, which are adiabatically connected to the photoproduct zone through a barrier along the reaction coordinate. Based on our set of results, we propose that an epoxide constitutes the most stable and accessible photoproduct preceded by the population of a triplet biradical of πOπ* nature which has only small geometrical differences in comparison with the reactant. The spin–orbit coupling indicates that the EPR signal arises due to the population of a low energy triplet through a thermally accessible intersystem crossing in the photoproduct zone.

Graphical abstract: The mechanism behind the photochromism and photomagnetism of type II biindenylidenediones: multiconfigurational, perturbative and density functional theory studies

Supplementary files

Article information

Article type
Paper
Submitted
19 Apr 2021
Accepted
24 Jun 2021
First published
24 Jun 2021

Phys. Chem. Chem. Phys., 2021,23, 17453-17465

The mechanism behind the photochromism and photomagnetism of type II biindenylidenediones: multiconfigurational, perturbative and density functional theory studies

P. J. Castro and M. Reguero, Phys. Chem. Chem. Phys., 2021, 23, 17453 DOI: 10.1039/D1CP01692J

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements