Fast and Reversible Luminescence “Turn-On” Detection of Ethanol Vapor by H‑Bonded Molecular Crystal Thin Film

Self-adaptive, semiconductive, and stimulus-responsive H-bonded molecular crystals have recently shown great promise for optoelectrical sensing applications. Herein, an ethanol vapor detector was exploited by using a luminescent H-bonded molecular crystal thin film, which was fabricated on the basis of an A–D–A photoactive molecule, 2,6-bis(pyridin-4-yl)-1,7-dihydrobenzo[1,2-d:4,5-d′]diimidazole. The title H-bonded molecular crystal, LYNU-10, shows significant concentration-dependent fluorescence emission in an ethanol solvent ranging from blue to orange. Remarkably, while being subjected to ethanol vapor, the H-bonded molecular crystal thin film shows fast and reversible fluorescence “turn on” with an extremely short response time of only 2.5 s and fluorescence intensity that is enhanced 1600-fold. The potential response mechanism was due to the ethanol-triggered phase change of H-bonded molecular crystal structures as evidenced by powder X-ray diffraction, scanning electron microscopy images, and density functional theory calculations.