Vapochromism and crystallization-enhanced emission of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles

Effects of solvent vapor on the photoluminescence (PL) of 2,3,4,5-tetraphenylsiloles carrying different 1,1-substituents [(PhC)(4)SiRR', R = Ph, R' = CH3 (2); R = Ph, R' = C equivalent to CH (3); R = R' = C equivalent to CH (4)] were investigated. The emission of the silole spots on the TLC plates can be turned "off" and "on" continuously and reversibly by wetting by, and de-wetting from, vapors of organic solvents, respectively. After fumigation by solvent vapor, the thin film of 4 coated on the quartz substrate emits stronger and bluer PL owing to the transformation of film morphology from the amorphous to the crystalline phase. Analysis by X-ray diffraction reveals that the molecular conformations of the crystals of 2-4 are locked and stabilized by multiple C-H center dot center dot center dot pi hydrogen bonds. This structural rigidification has made the silole crystals stronger emitters.