Polarization Dependence of Photothermally Resonated Natural Vibration in an Aminoanthraquinone Crystal

A thin plate-like 1,4-di-p-toluidinoanthraquinone (Solvent Green 3) crystal oscillats upon pulsed linearly polarized light based on photothermally resonated natural vibration. The crystal oscillates with different magnitude depending on the polarization direction of the incident light. This anisotropic oscillation originates from the anisotropic absorption, which is derived from the direction of the transition dipole moments.

Photomechanical organic crystals have gained considerable attention both from the perspective of fundamental research and applications in actuators and soft robots. Needle-like crystals of 1,4-di-p-toluidinoanthraquinone (1), an aminoanthraquinone derivative, oscillate when irradiated with unpolarized pulsed light, based on photothermally resonated natural vibration. However, their photomechanical motion in response to polarized light has not yet been investigated in detail. In this study, the photomechanical behavior of 1 upon linearly polarized light irradiation is examined. The crystal oscillats with a different magnitude depending on the polarization direction of the incident light. The greater the absorption, the larger and more significant the oscillation. Furthermore, the crystal exhibits different oscillation anisotropy depending on the wavelength of the light (375, 520, and 638 nm). This is because the crystal exhibits distinct absorption anisotropy depending on the wavelength of the light, which originates from the directions of the transition dipole moments. This work highlights that the polarization direction can serve as a control parameter, providing an additional degree of freedom to photomechanical crystals.

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