Achieving Organic Smart Fluorophores by Controlling the Balance between Intermolecular Interactions and External Stimuli

Organic smart fluorophores (OSFs) are highly desirable over the past decades because of their potential applications in advanced photonic devices. However, it is still difficult and challenging to obtain such materials with tunable photophysical properties and high emission efficiency based on robust construction strategies. Therefore, we proposed a simple and efficient strategy for constructing OSFs by balancing the competition between intermolecular interactions and external stimuli via molecular structure design. In this work, four pyrene derivatives (T1-Py, T4-Py, T12-Py, and S12-Py) with tunable stimuli-responsive properties were designed and synthesized. The tunable intermolecular interactions in solution states were successfully demonstrated by the molecular structure and solution concentration-dependent luminescence properties. The effect of alkyl chain length on molecular packing in solid states was investigated by polarized optical microscopy and powder and single-crystal X-ray diffraction; the results show that with the increase in molecular chain length, the molecular packing of the compounds gradually changed from π-π stacked compact mode to X-crossing stacked loose mode, which leads to different stimuli-responsive phenomena of these compounds. The strategy provided herein facilitates the construction of multistimuli-responsive (thermochromism, mechanochromism, and vapochromism) OSFs with adjustable emission color. Harnessing the heat-responsive luminescence properties and great solubility of T12-Py, the optical information anticounterfeiting based on temperature was demonstrated by printing different concentrations of T12-Py solution on filter papers. Much more, this research may provide broad implications for the design of organic smart materials based on intermolecular interactions.