Tuning the Temperature Dependence for Switching in Dithienylethene Photochromic Switches

Abstract

Diarylethene photochromic switches use light to drive structural changes through reversible electrocyclization reactions. High efficiency in dynamic photoswitching is a prerequisite for applications, as is thermal stability and the selective addressability of both isomers ring-opened and -closed diarylethenes. These properties can be optimized readily through rational variation in molecular structure. The efficiency with regard to switching as a function of structural variation is much less understood, with the exception of geometric requirements placed on the reacting atoms. Ultimately, increasing the quantum efficiency of photochemical switching in diarylethenes requires a detailed understanding of the excited-state potential energy surface(s) and the mechanisms involved in switching. Through studies of the temperature dependence, photoswitching and theoretical studies demonstrate the occurrence or absence of thermal activation barriers in three constitutional isomers that bear distinct π-conjugated systems. We found that a decrease in the thermal barriers correlates with an increase in switching efficiency. The origin of the barriers is assigned to the decrease in π-conjugation that is concomitant with the progress of the photoreaction. Furthermore, we show that balanced molecular design can minimize the change in the extent of π-conjugation during switching and lead to optimal bidirectional switching efficiencies. Our findings hold implications for future structural design of diarylethene photochromic switches.

Solvation Dependent Redox‐Gated Fluorescence Emission in a Diarylethene‐Based Sexithiophene Polymer Film

“…The diarylethene class of photochromic switches have been demonstrated to be highly versatile, e.g., for on/off control of molecular properties such as fluorescence, redox as well as photochemically triggered switching, etc., and hence their incorporation into polymer films offers considerable opportunities for photochemical and electrochemical control of surface properties …”

Ferrocene‐Grafted Photochromic Triads Based on a Sterically Hindered Ethene Bridge: Redox‐Switchable Fluorescence and Gated Photochromism

“…Among the most ideal candidates, diarylethenes (DAEs) undergo reversible conrotatory 6π‐electron photocyclization and cycloreversion, particularly bestowing excellent thermal irreversibility and outstanding fatigue resistance . Given the rapid rotation of aryl groups in traditional DAEs, most of them involve the same inherent deficiency, that is, the mixed parallel and antiparallel conformers in DAE framework cannot be separated efficiently, thereby greatly decreasing the photocyclization quantum yields . Previously, our group has reported a sterically hindered DAE system ( BTTE , Scheme a), in which the photoactive anti‐parallel conformer (ap‐ BTTE ) and photo‐inactive parallel conformer (p‐ BTTE ) can be fully separated by column chromatography due to the blocked rotation resulted from the high steric hindrance between benzobis(thiadiazole) bridge and bulky benzothiophene terminals .…”

Photochromic Diarylethenes with Heterocyclic Aromatic Rings: Correlation between Thermal Bistability and Geometrical Characters of Transition States

“…[10][11][12][13][14][15][16][17] Among the desired properties of organic photochromic compounds, the thermal bistability in the "on" and the "off" states is a very important factor that determines the applicability of the material since the storage of information or processing of signals requires the material to be sufficiently stable in both states. [18][19][20][21][22][23] To date, dithienyl-perfluorocyclopentene-based compounds have been demonstrated to possess excellent thermal stability in both the ring-open and the ringclosed states, owing not only to the favorable performance of the perfluorocyclopentene bridging unit but also due to the particular electronic character of the thiophene aryl rings. [24][25][26] The heterocyclic thiophene rings provide π-conjugation and optical response in the ultraviolet and 1 2 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 58 59 60 3 visible region, which serve as input and output signals in real applications.…”