Pyranone-Arylbenzene Molecules Controlled by the Competition of Local Excited State and Twisted Intramolecular Charge-Transfer State: Dual-State Emission, Polymorphism, and Mechanofluorochromism

The adjustment of the luminescent properties of materials according to different environments has always been a hot topic. Among them, the local excited (LE) state and the twisted intramolecular charge-transfer (TICT) state are important factors that affect the photophysical properties of compounds. Herein, four donor-acceptor pyranone-arylbenzene molecules were synthesized using pyranone (Pr) as the acceptor and phenyl (Ph), naphthalene (Np), anthracene (An), and pyrene (Py) as donors, respectively. The results of experiments and theoretical calculations show that the TICT state dominates the luminescent properties of Pr-Ph and Pr-Np, which results in fluorescence quenching in solution and solid states. However, Pr-An and Pr-Py are dominated by the LE state caused by rigid anthracene and pyrene, and the twisted molecular conformations avoid the strong pi-pi interactions, leading to dual-state emissions. Moreover, Pr-An has two completely different polymorphs, Pr-An-SB and Pr-AnYG, which emit sky-blue and yellow-green fluorescence due to different conformations and stacking arrangements, respectively. Both the polymorphs can be transformed into an amorphous state that emits dark cyan fluorescence upon grinding, revealing high-contrast mechanofluorochromic properties. Furthermore, Pr-An-YG can be converted into more stable Pr-An-SB by solvent fumigation, revealing vapochromic activity. This work provides some useful information for the development of fluorescent materials based on LE and TICT states.