  We develop a new general formulation to explore light-driven electron
transport through a single-molecule device with multiple pathways. Three
individual systems are proposed including (i) a two-terminal molecular junction
based on phenyl-acetylene macrocycle (PAM), (ii) PAM with three terminals, and
(iii) a parallel molecular circuit. The computations show that PAM-based
optoelectronic switches have robust large on-off ratios and weak-field
operating conditions, which are not sensitive to asymmetric molecule-lead
couplings. In addition, field-amplitude power laws for one- and two-photon
assisted tunneling are evident in the computational results, and the laws can
be proven by using perturbation analysis. For PAM-based optoelectronic routers,
we show that it is possible to manipulate the direction of electric current
through the PAM molecule by using a weak linearly polarized laser field. For
parallel circuits made of molecular quantum dots, the condition of coherent
destruction of tunneling is derived by using the rotating wave approximation
and the high-frequency approximation.
