Size-discrimination of volatile organic compounds utilizing gallium diiminate by luminescent chromism of crystallization-induced emission via encapsulation-triggered crystal-crystal transition

This manuscript describes the role of multi-functional gallium diiminate in photochemistry, crystal structural transition and molecular recognition. Discrimination of volatile organic compounds (VOCs) is a key technology to develop chemical sensors and probes such as for the detection of hazardous chemicals as well as for the assessment of air pollution. So far, there are several optical materials which can selectively capture some kinds of VOCs and present the alteration of optical properties. However, it is still rare to distinguish for only the size of VOCs by luminescent chromism regardless of chemical components of VOCs or functional groups in VOCs. This manuscript demonstrates that the size-dependent inclusion of the fumed VOCs into the solid-state emissive crystals of gallium diiminate can occur with the luminescent chromism of its crystallization-induced emission (CIE). In particular, it was shown that the degree of luminescent chromism was critically dependent not on the chemical components of the captured VOCs but on their radius of gyration (rg). Finally, it was also demonstrated that from the changes in the thermal and physical properties monitored through powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC) and diffuse reflectance profiles, the precise discrimination of the molecular sizes of VOCs by 0.1 angstrom was accomplished. From the structural analyses before and after fuming VOCs to the crystalline samples of gallium diiminate, it was revealed that the crystal-crystal structural transition was induced.