Conformational Emissive States in Dual-State Emitters with Benzotriazole Acceptors

Dual-state emission (DSE), the emission of organic molecules in solution and solid state, has recently drawn interest for advanced performance materials. Here, we report conjugated compounds 1 and 2 with good photoluminescence (PL) in solution (ΦPL = 0.53 and ΦPL = 0.43) and exceptional emission in the solid state (ΦPL = 0.92 and ΦPL = 0.84). These donor-π-acceptor-π-donor (D-π-A-π-D) compounds with rotary components adopt different highly emissive states, according to our PL measurements. Time-dependent density functional theory (TD-DFT) calculations indicate that the PL changes are facilitated by polarizable moieties, with the possibility of trapping in the higher energy S2 state and anti-Kasha emission in viscous solutions. Complementarily, the flexibility and symmetry (or the lack thereof) of each molecule play a critical role in producing strongly fluorescent twisted structures in the solid state.