Conical intersections and ultrafast intramolecular excited-state dynamics in nucleic acid bases and electron donor–acceptor molecules

Conical intersections play important roles in photochemistry and photobiology through their preeminent control over the course of electronic relaxation processes. In this Letter, we present results from a combined experimental and computational study of ultrafast internal conversion in nucleic acid bases and intramolecular charge transfer in N,N-dialkylaminobenzonitriles, which indicate that these photoprocesses occur through three-state conical intersections involving an intermediate electronic state.