Theoretical Study of Excited-State Dynamics of Hypercoordinated Carbon Molecule

Structural and dynamical aspects of vibronically coupled S1 (dipole-allowed, “bright”) and S2 (dipole-forbidden, “dark”) states of hypercoordinated carbon molecule, 1,8-dimethoxy-9-dimethoxymethylanthracene monocation, are investigated. Potential energy surfaces are modeled within the linear vibronic coupling scheme. Quantum dynamics simulation show that the nuclear wavepacket initiated on the “bright” S1 state would move to “dark” S2 within a few femtoseconds via an accessible conical intersection. A dynamical equilibrium of wavepacket exchange between S1 and S2 is observed after 50 fs of propagation time. The activity of vibrational motions associated with the hypercoordinated carbon and C−H vibrations is analyzed using the reduced nuclear densities. Our findings illustrate that the excited-state nonadiabatic behavior has to be taken into account while analyzing the optical properties of this hypercoordinated carbon molecule.