Nonadiabatic Dynamics of Charge-Transfer States Using the Anthracene-Tetracyanoethylene Complex as a Prototype.

Surface hopping quantum mechanical/molecular dynamics simulations have been performed for the tetracyanoethylene-anthracene complex to investigate the evolution of charge-transfer (CT) states after excitation into a locally excited (LE) state of anthracene. The scaled opposite-spin (SOS) second-order algebraic diagrammatic construction (SOS-ADC(2)) has been used to achieve a balanced description of LE and CT states. The calculations have been performed for two media, the gas phase and water (described by molecular mechanics, MM). The two dynamics variants show strongly different behaviors. Even though in both cases the conversion from the LE state to lower-lying CT states occurs with 100 fs, in the gas phase, the system remains in the excited state for longer than 2 ps, while in water, it returns to the ground state within 0.5 ps. Moreover, while in the gas phase the original neutral equilibrium structure should be recovered, in water, the ion-pair (IPr) CT state is strongly stabilized, creating a new competing ground-state isomer. Thus, we predict that the ground state of the complex in water should be composed of two species, the original neutral state and an IPr state. The existence of an IPr ground state in strongly polar environments opens interesting possibilities for the design of efficient charge-separating organic donor-acceptor interfaces.