Photochromic microresonator arrays with whispering gallery mode fingerprints are successfully prepared, which function as high-security optical authentication microdevices.

molecules, organic crystals have been exploited for a wide range of optical applications, including waveguides, resonators, solid-state lasers, and sensors. [1][2][3] As well-demonstrated by the success of organic dye lasers featuring a wide feasible wavelength range, organic chemistry enables the fine-tuning of the emission band in the visible region by the precise modification of the molecular structure and associated electronic energetics in the steady and transient states. [4] Recently, researchers are focusing on the control of the morphology of the crystal grains to further exploit the optical properties of organic crystals. Fu and co-workers conducted the crystallization of π-conjugated molecules in a small-droplet on a quartz substrate to form toroidal microcrystals, in which the molecular fluorescence circularly propagated and exhibited whispering gallery mode (WGM) optical resonance and lasing. [5] In 2020, our group reported a morphology-and molecular orientation-dependent lasing behaviors of fluorescent dendrimer crystals, in which light is confined via WGM and Fabry-Pérot (FP) mode. [6] Organic crystals described above represent a unique and emergent materials group in optics. Nonetheless, because of the extreme fragility against an external bending stress, these organic crystals are still far behind their inorganic counterparts, which limits applications of organic crystals to practical devices that require mechanical assembling or that involve mechanical oscillations and impacts during operation. Recently, some groups, including us, coincidentally reported the synthesis of mechanically flexible organic crystals (FOCs) and establish a molecular strategy for FOCs, which was then followed by enthusiastic progressions from many other groups. [7][8][9][10][11][12][13] Mechanically flexible elastic and plastic organic crystals that work as an optical waveguide and resonators even after bending have also been used to develop microscopic all-organic photonic integrated circuits. [14][15][16][17][18][19][20][21] Along this line, optical resonators made of FOCs are also sought after as a future wavelength-and direction-tunable laser emitter. [23,24] However, the synthesis of flexible organic crystalline resonators remains a fundamental challenge so far because of the inherent optical loss during the light propagation along the longitudinal direction and the reflection at the end facets. [17,18] Tuning resonance properties by mechanical bending is, therefore, a far more formidable challenge in terms of both crystal engineering and optics.An organic single-crystal optical resonator that maintains its optical performance even upon mechanical bending remains a challenging target. Here, the first flexible organic crystal (FOC) that works as a tunable optical resonator as a function of bending angle is developed. A fluorescent π-conjugated molecule, cyano-substituted oligo(phenylenevinylene)s, is allowed to crystallize slowly, yielding a discrete rod-shape microcrystal (FOC COPV ). FOC COPV not only works as an ef...

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NIR WGM resonators are fabricated from energy-donating and accepting conjugated polymers.

Skeletal or concave polyhedral crystals appear in a variety of synthetic processes and natural environments. However, their morphology, size, and orientation are difficult to control because of their highly kinetic growth character. We report a methodology to achieve synchronous, uniaxial, and stepwise growth of micrometer-scale skeletal single crystals from planar-chiral double-decker molecules. Upon drop-casting of a heated ethanol solution onto a quartz substrate, the molecules spontaneously assemble into standing vessel-shaped single crystals uniaxially and synchronously over the wide area of the substrate, with small size polydispersity. The crystal edge is active even after consumption of the molecules and resumes stereoselective growth with successive feeding. The resultant morphology can be packed into polycyclic aromatic hydrocarbon–like microarchitectures and behaves as a microscopic container.