Model for Photoinduced Bending of Slender Molecular Crystals

Abstract

The growing realization that photoinduced bending of slender photoreactive single crystals is surprisingly common has inspired researchers to control crystal motility for actuation. However, new mechanically responsive crystals are reported at a greater rate than their quantitative photophysical characterization; a quantitative identification of measurable parameters and molecular-scale factors that determine the mechanical response has yet to be established. Herein, a simple mathematical description of the quasi-static and time-dependent photoinduced bending of macroscopic single crystals is provided. This kinetic model goes beyond the approximate treatment of a bending crystal as a simple composite bilayer. It includes alternative pathways for excited-state decay and provides a more accurate description of the bending by accounting for the spatial gradient in the product/reactant ratio. A new crystal form (space group P21/n) of the photoresponsive azo-dye Disperse Red 1 (DR1) is analyzed within the constraints of the aforementioned model. The crystal bending kinetics depends on intrinsic factors (crystal size) and external factors (excitation time, direction, and intensity).

Dual Stress and Thermally Driven Mechanical Properties of the Same Organic Crystal: 2,6-Dichlorobenzylidene-4-fluoro-3-nitroaniline

“…Recent research has uncovered several crystalline systems that show different responses when they are subjected to external stimuli. 8,[18][19][20][21][22][23][24][25][26][27][28] These durable and resilient compounds are becoming increasingly important; their highly ordered structures can sustain efficient charge transport. However, the design of such solids, in which rapid and reversible macroscopic shape changes are enabled through collective molecular perturbations, remains a challenge.…”

Quantitative Evaluation of Photoinduced Bending Speed of Diarylethene Crystals

“…The correlation between the initial speed of the curvature change and the crystal thickness was well explained by the Timoshenko's bimetal model in both types of bending, bending away from UV light and bending toward UV light. Naumov and Bardeen have also independently reported the more sophisticated mathematical treatments based on the fact that the concentration of the photoreacted product throughout the crystal continuously changes for other phoreactive compounds [35,36]. Such a rigorous analysis of the experimental fact is necessary for the development of the research field.…”

Spatially resolved analysis of short-range structure perturbations in a plastically bent molecular crystal

“…To rationalize the dynamical effects of bendable single crystals, the simple qualitative mechanistic models advanced in the past have repeatedly resorted to using the internal misfit strain, which is induced by the non-uniform distribution of product in the crystal lattice of the reactant [30][31][32][33][34] . However, obtaining a deeper understanding and quantification of the atomistic-scale structural perturbations that alter the elastic and optical properties during such deformations is challenging, and necessitates significant experimental engagement [35][36][37] .…”