Photochromism of 1,2-Bis(2-thienyl)perfluorocyclopentene Derivatives: Substituent Effect on the Reactive Carbon Atoms

Photo-cycloreversion mechanism in diarylethenes revisited: A multireference quantum-chemical study at the ODM2/MRCI level

Photoswitchable diarylethenes (DAEs), over years of intense fundamental and applied research, have been established among the most commonly chosen molecular photoswitches, often employed as controlling units in molecular devices and smart materials. At the same time, providing reliable explanation for their photophysical behavior, especially the mechanism of the photo-cycloreversion transformation, turned out to be a highly challenging task. Herein, we investigate this mechanism in detail by means of multireference semi-empirical quantum chemistry calculations, allowing, for the first time, for a balanced treatment of the static and dynamic correlation effects, both playing a crucial role in DAE photochemistry. In the course of our study, we find the second singlet excited state of double electronic-excitation character to be the key to understanding the nature of the photo-cycloreversion transformation in DAE molecular photoswitches.

A deeper look into the photocycloreversion of a yellow diarylethene photoswitch: why is it so fast?

The DMT photoswitch features an efficient ring-opening reaction at a sub-picosecond timescale owing to a single-channel relaxation from the S₁ state which leads to a conical intersection with the ground state.

Core structure dependence of cycloreversion dynamics in diarylethene analogs

Increased core rigidity in diarylethene-type photoswitches results in shallower excited-state potential energy surfaces and faster funneling towards the conical intersections from which cycloreversion and nonreactive deactivation occur.

Cyclization reaction dynamics of an inverse type diarylethene derivative as revealed by time-resolved absorption and fluorescence spectroscopies

Photocyclization reaction dynamics of an inverse type diarylethene derivative was investigated in alkane solutions by means of ultrafast laser spectroscopies. Femtosecond transient absorption spectroscopy showed that the Franck-Condon state formed by photoexcitation is geometrically relaxed to a transient species within 100 fs and subsequently the cyclization process takes place with a time constant of 36 ps. This time constant is much longer than those in normal type derivatives. Steady-state and time-resolved fluorescence measurements with the aid of quantum chemical calculations revealed that there exist three kinds of conformers, one parallel and two anti-parallel forms, in the ground state. One of the anti-parallel conformers undergoes the cyclization reaction, while the other two conformers are nonreactive species and their major relaxation processes are radiative decay and intersystem crossing into the triplet states. The triplet states thus formed no longer undergo the cyclization reaction in the late time region.

Theoretical analysis of electrochromism under redox of bis(3-thienyl)/(2-thienyl)hexafluorocyclopentene: effects of charged and substituted systems

Electrochromism with the ring-closing or ring-opening isomerization of substituted and unsubstituted bis(3-thienyl)/(2-thienyl)hexafluorocyclopentene is discussed using the DFT method. In the neutral ground state, bond making and breaking between two reactive C atoms on thienyls are thermodynamically forbidden. Under redox conditions, the gain or loss of electrons can have a significant effect on the frontier molecular orbital distribution of both open- and closed-ring isomers, particularly in reactive sites. Corresponding structural changes show a trend toward isomerization. The reaction energy barrier shows greater reduction for dication than monocation and even becomes barrierless for dianion. During the isomerization in different states, the conjugated system switches distinctively, which is attributed to the special redistribution of molecular orbitals and spin population in each state. In monocation and monoanion, for the involvement of a single electron, isomerization is inclined to proceed sequentially between right and left thienyls, whereas it becomes synchronous in dication. The direction depends on the stabilization achieved by the formation of a global conjugated system and more average spin population on the molecule. The effect of substituents on thienyls is demonstrated in the promotion of the extent of conjugation and the determination of the spin population level on the reactive C atoms. Moreover, according to their electron-donating and withdrawing abilities, they can kinetically support or suppress the electron transfer pattern in the process from isomer to transition state, which leads to the control of reaction efficiency.

Optical spectrum, perceived color, refractive index, and non-adiabatic dynamics of the photochromic diarylethene CMTE

Photochromism allows for reversible light-induced conversion of a molecular species into a different form with significantly altered optical properties. One promising compound that excels with high fatigue resistance and shows its photochromic functionality both in solution and in molecular solid films is the diarylethene derivative CMTE. Here we present a comprehensive study of its photophysical properties with density-functional theory based methods and benchmark the results against higher-level quantum-chemical approaches and experiments. In addition to static properties such as optical absorption, perceived color, and refractive index, we also investigate reaction dynamics based on non-adiabatic ab initio molecular dynamics. This gives detailed insight into the molecules' ultrafast reaction dynamics and enables us to extract reaction time scales and quantum yields for the observed electrocyclic reaction following photoexcitation.

Substitution effect on the photochromic properties of benzo[b]thiophene-1,1-dioxide based diarylethenes

Benzo[b]thiophene-1,1-dioxide based diarylethenes containing methyl, phenyl, formyl and triphenylamine groups are developed for taking insight into substituent effects on the absorption properties and photochromism.

Competitive direct vs. indirect photochromism dynamics of constrained inverse dithienylethene molecules

Relaxation observed through several parallel pathways from the first excited state to the ground-state in inverse dithienylethene molecules.

Perfluorocyclohexene bridges in inverse DiArylEthenes: synthesis through Pd-catalysed C-H bond activation, experimental and theoretical studies on their photoreactivity

The palladium-catalysed direct di-heteroarylation of 1,2-dichloroperfluorocyclohexene with a variety of heteroarenes gives rise in to a new family of 1,2-di(heteroaryl)perfluorocyclohexenes. These derivatives do not exhibit photoreactivity and this unexpected outcome is explained by calculations demonstrating the lack of reactive isomers.

Potential energy surfaces and quantum yields for photochromic diarylethene reactions

Photochromic diarylethenes (DAEs) are among the most promising molecular switching systems for future molecular electronics. Numerous derivatives have been synthesized recently, and experimental quantum yields (QYs) have been reported for two categories of them. Although the QY is one of the most important properties in various applications, it is also the most difficult property to predict before a molecule is actually synthesized. We have previously reported preliminary theoretical studies on what determines the QYs in both categories of DAE derivatives. Here, reflecting theoretical analyses of potential energy surfaces and recent experimental results, a rational explanation of the general guiding principle for QY design is presented for future molecular design.