Electron donor and acceptor functionalized dithienylethenes: effects of charge density on photochromic properties

Abstract

Electron-donating triphenylamine and/or electron-withdrawing pyromellitic diimide (PMDI) are functionalized on dithienylethene (DTE) and three novel photochromic materials have been designed and successfully synthesized. All the compounds display reversible photochromism due to the molecular switching between ring-closed isomers upon UV light irradiation and ring-open isomers upon exposure to visible light. Thus they can be applied as an anti-counterfeiting ink. Moreover, the study of the photoswitching kinetics reveals that both the ring-closing and ring-opening reactions are first-order reactions. Further charge population analysis discovers that the electron densities of the substituents at the DTE core have a dramatic influence on the photochromic properties. The incorporation of electron-donating triphenylamine groups at the α-position of the thiophene rings in the DTE unit facilitates the ring-closing reaction upon UV light irradiation. In contrast, the substitution of an electron-withdrawing PMDI unit in the DTE unit is beneficial to the ring-opening reaction upon irradiation of visible light. This work may help to understand the photochromism of DTE derivatives and provide a pathway for designing DTE-based photochromes with more or less sensitivity to UV or visible light.

Light-Triggered Metal Coordination Dynamics in Photoswitchable Dithienylethene–Ferrocene System

“…This slower kinetics of ring closing in the metal-chelated form, [ 3o ·Hg 2+ ], was also supported by the lower (8.2 times) quantum yield (Φ o→c ) of 0.068 (Figure S18 and Table S3), in comparison to that of free 3o . This shows that, although [ 3o ·Hg 2+ ] gets converted to [ 3c ·Hg 2+ ], the rate of conversion of free 3o to 3c ( k = 0.01 s –1 ) is faster than the rate of conversion of [ 3o ·Hg 2+ ] to [ 3c ·Hg 2+ ] ( k = 0.007 s –1 ), as is also confirmed by kinetic studies, using UV–vis spectra (Figure S19). The binding equilibrium in 3c is not being as stable as that for the open isomer may be due to the formation of a strained and puckered five-membered C–S–Hg–S–C ring, as indicated by DFT calculations ( vide infra ).…”

On-demand regulation of photochromic behavior through various counterions for high-level security printing

“…In particular, the abil ity to tune the coloration rate on demand can significantly improve the security level of the recorded texts, because different informa tion would appear using various irradiation times. To date, progress has been made in the regulation of colorability and coloration rates by incorporation of electron donor or acceptor substitutions in photo chromic molecules (17,18). Nevertheless, the prepared photochromic materials generally have constant colorability and coloration rates under the same light irradiation condition (19)(20)(21)(22)(23)(24)(25).…”

High response photochromic films based on D–A diarylethenes and their application in holography

“…Notably, the two symmetric molecules, have been already reported in the literature for improving the cycloreversion by means of a complexation (AmAm) 29 and for the development of anti-counterfeiting inks (TrfAm), 30 showing the effect on the switching properties. The asymmetric derivative (NtAm) was study from a theoretical point of view to evaluate the nonlinear optical properties.…”