Large blue shifted photoluminescence spectra of silole crystals relative to the amorphous form

We synthesized two new siloles with thiophene linkage to the silicon atom that could show aggregation-induced emission (AIE), and observed that their PL emissions strongly depended on the aggregation states. The siloles are virtually nonemissive in solutions but their aggregates or solid films are highly luminescent, and the PL spectra of crystals of the siloles show large and unusual blue shift compared to the amorphous state. These phenomena are unique since PL quantum yields of conjugated organic emitters normally decrease in solid states, along with red shift of PL spectra at higher aggregation extent. Different and variable PL spectra of aggregates of the siloles formed in water/acetone mixtures were found. At certain water fraction, the solvent mediated aggregation morphology changing from the amorphous state to the crystalline state probably resulted in the variable PL emissions of the silole aggregates. Our results reveal that the novel thiophene containing siloles are crystalline blue emitters, and only their crystalline forms, rather than the amorphous forms, can emit lights with stable PL spectra.