Inverse versus Normal Dithienylethenes: Computational Investigation of the Photocyclization Reaction

Abstract

The understanding of the intimate electronic processes in photochromes is essential to optimize the properties of light-controllable devices. For one of the most studied classes of molecular switches, namely, dithienylethenes, the relative efficiencies of the normal and inverse structures remained puzzling. Indeed, despite a larger ratio of the active antiparallel conformers for the latter, the quantum yields of cyclization of inverse dithienylethenes do not exceed those of its normal counterpart. In the present contribution, we provide the first explanation of this experimental outcome using multireference ab initio quantum chemistry. We demonstrate the existence of a fluorescent intermediate on the S 1 state of the inverse system that generates a photochemically unreactive conformation in the ground state. This study paves the way toward a rational development of efficient molecular photochromes presenting a photon-quantitative response.

Molecular Photoswitching Aided by Excited‐State Aromaticity

“…In closing, we emphasize that the potential of using ESA as a photochemical design tool is heavily unexplored. Therefore, given the positive results reported in this minireview and the proven merits of computational modeling in studies of molecular photoswitches, [83][84][85][86][87] it appears worthwhile for future research to investigate whether the ESA concept also can be employed to improve molecular photoswitches in other aspects than those discussed herein. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57…”

A curve-crossing model to rationalize and optimize diarylethene dyads

“… 21 – 23 , 25 The S 2 state also plays a role, as it interacts with the S 1 state through an ionic/covalent mixing that changes the electronic character of S 1 when going from the FC region to the S 1 / S 0 CI. 21 , 25 Hereafter, we will ignore this latter aspect and simply consider that each DAE unit is characterised by two electronic states, S 0 and S 1 , the ground state and the first bright excited state, respectively. A simplified correlation diagram for these adiabatic states along a ring-opening/closing reaction coordinate can thus be built, where a valence-bond-type (VBT) state, 34 denoted C, correlates the S 0 closed isomer c-A to the S 1 open isomer o-A* while a second VBT state, denoted O, correlates the S 0 open isomer o-A to the S 1 closed isomer c-A* (see Fig.…”

Cyclization Dynamics and Competitive Processes of Photochromic Perfluorocyclopentene Dithienylethylene in Solution

“…Based on those results, we can emit a new hypothesis concerning the nature of the X species: rather than originating from CF reexcitation, the by-product reported for diarylethene could come from the triplet of the P conformer of the OF. As an evidence, advanced CASSCF/CASPT2 calculations already performed for model DTEs [29] are now desired to explore the pathways starting from either CF* or from P* species evolving trough the X singlet biradical structure to finally giving birth to the by-product molecule. Just as challenging, the interconversion between AP and P at both singlet and triplet manifold have to be included.…”

“…[22,23] Indeed, the rationalization of complex excited state mechanisms are highly desired to still improve photochromic performances and so considerable investigations have been devoted worldwide to explore the excited state topologies of DTEs (or DAEs) via advanced optical spectroscopies [24][25][26][27] and/or computational chemistry. [28][29][30] In this perspective, our group has actively investigated the spectrokinetic features on the series of bridged DAEs, [31] bridged DTEs [29,32,33] or DTEs dedicated to supramolecular chemistry [34] using ultrafast spectroscopies combined with (TD)-DFT calculations. Our leitmotiv was the attempt to detangle the photochemistry of the antiparallel (AP) conformers from the photophysics of parallel (P) conformers by comparing bridged/ constrained versus free analog molecules (the initial purpose of the former being the blockade of the molecule into a photoactive conformation).…”