White light from dual intramolecular charge-transfer emission in a silylene-bridged styrylcarbazole and pyrene dyad

Styrylcarbazole linked to pyrene by a dimethylsilyl bridge was synthesized in the search for new charge-transfer active materials for LED applications. In the course of a photophysical study, it turned out that such a donor-bridge-acceptor compound displayed three completely different types of emission depending on solvent polarity. The most attractive emission properties were found in acetonitrile in which two broad emission bands were observed. The resolved mechanism of the excited-state processes in acetonitrile was supported by singular value decomposition with self-modeling treatment of time-resolved emission spectra (ns-TCSPC). The data analysis revealed that there were two excited-state processes, that is, charge transfer within styrylcarbazole and electron transfer from styrylcarbazole to pyrene through a silylene bridge that was responsible for a broad dual emission. The general idea of designing compounds that display emission from more than one excited state covering a wide range of the visible spectrum can be a powerful tool in designing new white-light-emitting materials.