High-contrast fluorescence modulation driven by intramolecular photocyclization and protonation of bithienylpyridine functionalized α-cyanostilbene

We report herein a light-inducible fluorescence conversion and an acidochromism based on the bithienylpyridine functionalized α-cyanostilbene luminogen (E-CTP). The thienylcyanostyrene unit in this luminogen endows E-CTP AIEE property and 365 nm light-induced fluorescence conversion with high contrast in color (Δλem = 85 nm) and strong intensity. The fluorescence conversion of this molecular system might be driven by an intramolecular photocyclization rather than the commonly occurred intermolecular photodimerization for the α-cyanostilbene system as indicated by UV, PL, TCL-MS as well as NMR spectra measurements. Due to the bithienyl-pyridine in its skeleton, the optoelectronic properties of this luminogen can also be tuned by protonation. The luminogen shows 6 fold fluorescence enhancement and 110 nm emission red-shift in solution upon addition of trifluoroacetic acid (TFA). The optical feature of the reversible recoverability for E-CTP under acid-base stimuli in film was utilized to prepare security paper. Moreover, cooperating the acidochromism with the photo-induced fluorescence conversion of E-CTP, multicolor light-painting pattern was achieved.