Crystal Structures and Photophysical Properties of 9-Anthracene Carboxylic Acid Derivatives for Photomechanical Applications

Abstract

Molecular crystals composed of 9-anthracene carboxylic acid (9AC) can undergo reversible light-induced mechanical motions driven by a [4 + 4] photodimerization reaction. This paper explores the structure, photophysics, and photomechanical response of a family of anthracene carboxylic acid derivatives, with the goal of finding materials that have comparable or improved photomechanical properties. We find that methyl or phenyl substitution at the 10-position leads to a complete loss of photoreactivity due to changes in crystal packing. A series of halogen (F, Cl, Br) 10-substituted 9AC molecules all showed a similar stacked packing motif, but only the fluoro-substituted molecule was photoreactive in the solid. Its photomechanical response was similar to that of 9AC but with a much longer recovery time. Extending the carboxylic acid by adding a vinylene group at the 9-position resulted in crystals that showed good photoreactivity and a lack of fracture but no reversibility. Attempts to self-consistently rationalize observed trends in terms of excited state lifetimes or steric effects were only partly successful. Balancing factors such as electronic relaxation, steric interactions, and crystal packing present a challenge for engineering photoactive solid-state materials based on molecular crystals.

Hybrid Nanoscale Organic Molecular Crystals Assembly as a Photon‐Controlled Actuator

“…[11][12][13][14][15][16][17][18] Macroscale molecular crystals rarely present ideal deformation properties and it is still a challenge to use molecular crystals in macroscale actuators. Nevertheless, molecular crystal actuators are fragile and are highly restricted in performance by the crystal size and shape.…”

Quantitative Evaluation of Photoinduced Bending Speed of Diarylethene Crystals

“…Various types of photomechanical behaviors such as contraction [8,10], expansion [11], OPEN ACCESS bending [8,[11][12][13][14][15][16][17], separation [18], twisting [19], and rolling [12] have been reported so far. Although photochromic compounds such as diarylethenes [8,19], furylfulgide [20], azobenzene [21,22], anthracene carboxylates [23][24][25][26][27][28], salicylideneaniline [29], 4-chlorocinnamic acid [30], 1,2-bis(4-pyridyl)ethylene salt [31], benzylidenedimethylimidazolinone [32], and others [33] exhibit photochemical reactions in the crystalline phase, their photomechanical motions in the crystal are almost bending. It is essential for the development of the research field of photomechanical crystals to investigate the crystal bending behavior in detail.…”

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

“…T he growing recognition that rapid energy transfer between molecules of tightly packed, ordered crystals of molecular solids could be utilized as a physical platform for actuation from the nanoscale to the macroscale has recently boosted research on mechanically responsive organic-based molecular crystals [1][2][3][4][5][6][7][8][9][10][11][12] . This rapidly expanding research field has revealed an increasing number of examples of oftentimes serendipitous observations of nano-, milli-and macro-sized single crystals that hop [12][13][14] , bend [15][16][17][18][19][20] , curl 21,22 , twist [23][24][25] or swim 26 when exposed to light, heat or external pressure.…”