Prediction of Half-Life Time in Thermal Back Reaction of Photochromic Diarylbenzenes by Screening Approach

Abstract

Diarylbenzenes (DABs) have been developed as a novel family of T-type photochromic compounds. In this work, we endeavored to predict the half-life time (t1/2) in the thermal back reaction of DABs by a screening approach. By the combination of experimental and theoretical studies, we found a good relationship between the t1/2 and the activation energy estimated by theoretical calculations. Our results would provide useful information for the design of DABs having a desired thermal stability.

Diarylethene-Type Photochromic Electron Traps Extending Narrow Linear Dynamic Range of Organic Photodetectors. Design Principles and Fate After Electron Transfer. Self-Destructive or Self-Protective?

“…For neutral DAE before trapping electrons (Figure 3a, black curve), in agreement with previous reports, 43,44,86,87 DAE-c is less stable than DAE-o in both cases (4F/6F-T-H-Ph or simply 4F/6F), but the amount of destabilization ΔE o→c (= −ΔE c→o ) is greater for 4F-T-H-Ph [1.10 vs 1.15−1.21 (calc) 43,44 ] than for 6F-T-H-Ph [0.54 vs 0.58 (calc) 43 ] and the thermal cycloreversion activation energy E a(c→o) is smaller for 4F-T-H-Ph [0.76 vs 0.68 (exp) 43,44 and 0.60 (calc) 43,44 ] than for 6F-T-H-Ph [1.42 vs 1.44 (exp) 43,86 and 1.33 (calc) 43 ]. When the standard free energies at 298 K (ΔG = E + ZPE + ΔΔG 0→298 K ) with zero-point-energy (ZPE) and thermodynamic (ΔΔG 0→298 K ) corrections are used to evaluate E a(c→o) , the discrepancy from experiment is now smaller (0.66 vs 0.68; 4F-T-H-Ph), but such corrections make little difference in overall energetics while being time-consuming due to the normal-mode analyses.…”

“…(i) Fluorinated head groups are chosen as R 0 of n-type dopants to lower the HOMO and particularly LUMO energies, thus reducing the HOMO–LUMO gap and increasing the electrochemical potential and the fatigue resistance. , In particular, diarylbenzene (4F) loses a significant amount of aromaticity after cyclization, leading to a destabilization of DAE-c and a small activation energy for cycloreversion. ,, Photogenerated DAE-c of such a type reverts to DAE-o not only by photoreaction but also by thermal reaction.…”

“…58,59 In particular, diarylbenzene (4F) loses a significant amount of aromaticity after cyclization, leading to a destabilization of DAE-c and a small activation energy for cycloreversion. 43,44,60 Photogenerated DAE-c of such a type reverts to DAE-o not only by photoreaction but also by thermal reaction.…”

“…The latter condition is particularly imperative to check, because a self-destructive electron acceptor undergoing a fast C–C bond cleavage in anionic states (which corresponds to the ring opening of DAE-c as soon as it accepts electrons) has been reported (probably due to the antibonding character of the newly occupied LUMO of the anion). It is true that the n-type trap chosen in the experiment, 1,2-bis­(2-methyl-5-(4-cyanobiphenyl)-3-thienyl) tetrafluorobenzene (4F-T-H-PhPhCN, Figures a and ), undergoes fast thermal (T-type, instead of photochemical P-type) cycloreversion (i.e., ring opening from DAE-c to DAE-o) even in the solid state. , Even a UV/visible spectroscopy could not be performed on the closed isomer due to its extremely fast cycloreversion . If cycloreversion occurs so fast after trapping electrons (to a level of immediate self-destruction of the DAE-c electron acceptor), it raises a question whether such electron traps would survive long enough to induce the desired photomultiplication behavior, although it may be beneficial for open-isomer recovery for the next cycle.…”