Effects of substitution with donor-acceptor groups on the properties of tetraphenylethene trimer: Aggregation-induced emission, solvatochromism, and mechanochromism

Luminescent materials with aggregation-induced emission (AIE) property have attracted considerable interests for their promising applications in light-emitting and display devices and fluorescent probes for chemo- and biosensors. Tetraphenylethene (TPE) derivatives are the most attractive species for their notable AIE performance, facile synthesis, and flexible structure modification. To study the effects of donor and acceptor substitutions and extend the applications of TPE-based materials, three TPE kindred, TTPE, BTPEFN, and BATPEFN, are employed. TTPE film displays efficient green fluorescence (λ_em = 494 nm, Φ_F = 100%), evident AIE characteristic (α_AIE = 154), and reversible mechanochromism by grinding-fuming: from blue (λ_em = 472 nm) to green emission (λ_em = 505 nm). Replacing two phenyls by two cyano (A) groups on the central TPE moiety derives BTPEFN, whose film shows efficient orange fluorescence (λ_em = 575 nm, Φ_F = 100%) and evident AIE (α_AIE = 13). The mechanochromic behavior of BTPEFN (from yellow to orange emission, λ_em from 541 to 563 nm) is reversible by repeating both the grinding-fuming and grinding-annealing processes. The cyano groups bestow BTPEFN with evident intramolecular charge transfer (ICT) property, the emission color can be tuned from green to red-orange by changing solvent from hexane to THF, while the emission of TTPE shows much less response to solvent polarity. Cyanos also endow BTPEFN with better self-assemble ability in proper conditions, and the obtained regular microribbons emit bright green fluorescence. Further decoration of BTPEFN with N,N-diethyamino (D) groups results in BATPEFN. Due to the cooperative effects of D and A groups, BATPEFN shows dramatic red-shifted fluorescence (λ_em = 713 nm), evident ICT process, and enhanced solvatochromism (from red to infrared).