Switching Photomechanical Response by a Structural Phase Transition in a Naphthalene Diimide Derivative

Abstract

A newly prepared photoresponsive material, specifically a naphthalene diimide molecule containing alkylamino groups, was found to exhibit a structural phase transition in the crystalline state. The phase transition dramatically altered the molecular arrangement from orthogonal π‐π stacking to parallel π‐π stacking. The photomechanical response of each crystal was also changed before and after the phase transition. While the as‐prepared crystal immediately responded to light irradiation (λ=370 nm), the responsiveness of the crystal became slower after heat treatment. Upon light irradiation, radical species, such as the radical anion, radical anion dimer, and mixed valence species, were formed, which have nearly the same distribution in both phases. However, the spin system and the structure of the radical anion were quite different from each other and were found to be sensitive to the molecular arrangement. The photo‐responsiveness of the crystals was corroborated by evaluating the relaxation of the radical anion.

Energy Conversion in Single‐Crystal‐to‐Single‐Crystal Phase Transition Materials

“…Smaller or thinner crystals often deform more easily than larger ones, especially for the photoresponsive crystals. [64,[216][217][218] The strain accumulated before phase change is more easily released in small crystals, and the occurrence of phase change is more difficult in higher density crystals with tightly packed crystal lattices. [218,219] Naumov and co-workers studied the relationship between the type of mechanical effect and crystal morphological scales (crystal length, width, thickness, and volume) during their phase transition.…”

“…[216] Likewise, Goto et al found that the repeatability of the bending motion was related to crystal thickness in naphthalene diimide derivative crystals. [217] The switching photomechanical responsive crystal tends to bend if its thickness is less than 30 µm, whereas a thicker crystal do not show any bending. Apparently, reducing the size of crystal is beneficial for phase transition and motion.…”

Naphthalene Diimide-Based Donor–Acceptor–Donor Small Molecules as Metal-Free Organocatalysts for Photocatalytic CO2 Reaction

“…Naphthalene diimide (NDI) is an attractive acceptor block for building low bandgap and n-type conjugated polymers because of its excellent electron-withdrawing ability and charge transport properties. 27 Thus, NDI-based materials have been widely used in several applications, including chemical sensors, 28 molecular switching devices, 29 photovoltaic devices, 30 and catalysts. 31 However, the potential for using NDIbearing organic small molecules as photocatalysts for CO 2 reduction remains unexplored.…”