Synthesis, photoluminescence and stimuli-responsive properties of multifluorinated tetraphenylethylene-based dialdehydes

Abstract

Through the synergistic effects of substituents, it may be possible to fine-tune the stacking structures and luminescence properties of organic light-emitting compounds. In this work, four tetraphenylethylene (TPE) derivatives (1–4) with different numbers of fluorine/formyl substituents at different positions were synthesized via Suzuki–Miyaura cross coupling reactions. Compounds 1 and 2 feature two formyl groups at the 3-position of the phenyl rings, while 3 and 4 carry two formyl groups at the 4-position. Among these, 1 and 3 are difluorinated derivatives, whereas 2 and 4 are tetrafluorinated ones. Owing to the distinct substitution patterns, compounds 1–4 exhibit varying aggregation-induced emission (AIE) behaviors in THF/H₂O and distinct mechanofluorochromic properties in the solid state, compared to their fluorine-free and monoaldehyde analogues. Notably, compound 3 demonstrates a high solid-state luminescence quantum yield of 0.89 without mechanochromism, while compound 4 exhibits a pronounced mechanochromic red-shift of 52 nm, significantly larger than those observed for the other TPE derivatives. In contrast, compounds 2 and 3 showed no mechanofluorochromism under the same conditions. Remarkably, compound 1 displays excitation-dependent emissions across all aggregated states (crystal, powder, ground and fumed/annealed ground samples), a feature absent in the other compounds. Compared to the TPE analogues with only fluorine substituent, the two formyl groups induced emission red-shift and enhanced stimuli-responsive properties. In addition, compound 3 exhibits faster fluorescent chemosensing towards hydrazine than its non-fluorinated analog.