Tight-binding study of interaction time in molecular switches

A characteristic switching time, associated with an impurity embedded in a tight-binding polyene chain, is developed. The modulated-energy traversal time, derived for potential models, is modified to the tight-binding situation. Since the traversal time takes into account the physical distance propagated, which is a meaningless concept in the context of the tight-binding model, we obtain an interaction time that measures the delay in tunnelling through the impurity site. The switching time is discussed in terms of the impurity-parameter space. {} 1996 The American Physical Society.