“…An alternative design based on superexchange mechanism 18 -20 of electronic coupling through a bridge ͑B͒ moiety in a donor-bridge-acceptor ͑DBA͒ complex has become a major motive in studies of long-range ET. [21][22][23][24][25][26][27][28][29][30][31][32] Although the superexchange coupling also decays exponentially with the DA separation, 6,26 the existence of a manifold of B states offers substantial flexibility for chemical design. A wide variety of bridging media including hydrocarbons, 27 proteins, 10,28,29,33,34 DNA, [35][36][37][38] and polyenes 39,40 has been considered for linear or bent DBA complexes.…”