How do substituents affect silole emission?

Researchers are in constant pursuit of solid-state emitters with high emission efficiency, excellent photostability and large Stokes shift. Among them, siloles are good representatives. In this paper, we report the effect of substituent on the emission of silole. 1,1,3,4-Tetraphenylsilole (TPS) is weakly emissive at 392 nm in both solution and aggregated states. Progressive attachment of the trimethylsilylethynylphenyl (TMSEP) group to the 2,5-positions of TPS generates TPE-TMSEP and TPS-2TMSEP, which emit intensely at 491 nm and 517 nm, respectively, in the condensed phase despite their solutions giving almost no light upon photoexcitation. High solid-state quantum yields of up to 91% are deduced from their solid powders, demonstrating a phenomenon of aggregation-induced emission (AIE). Restriction of the low-frequency motions is proved to be the main cause of the AIE effect. Conformational study and theoretical calculation show that the steric and electronic effects contributed by the 3,4- and 2,5-substituents are crucial for the silole emission.