A Molecular Router for Excited-State Energy: Revealing the Solvent-Controlled Competition between Charge and Proton Transfer

The integration of ICT and ESIPT typically suffers from a "1 + 1 ≠ 2" problem. Here, we report an azine-based compound exhibiting a unique solvatochromic switch between dual and single emission. This phenomenon is attributed to a solvent-gated competition: ICT on the S1 state and ESIPT on the S2 state. Increasing solvent polarity kinetically blocks the S2-ESIPT pathway by elevating the energy of the S1/S2 conical intersection, routing the emission exclusively to the S1-ICT channel. This finding reveals a new strategy for controlling excited-state dynamics.