SUPPRESSION OF THE HARPOONING MECHANISM IN DONOR-BRIDGE-ACCEPTOR SYSTEMS BY AZA SUBSTITUTION IN THE BRIDGE

An aza substituent was introduced in the bridge of donor-bridge-accept or systems known to undergo harpooning (long-range photoinduced charge separation followed by electrostatically driven folding). Although th e substitution does not reduce the conformational flexibility of the b ridge, it fully suppresses the harpooning mechanism. From a comparison with a reference compound, the solvatochromic shifts of charge transf er fluorescence and transient absorption results, it is concluded that suppression is due to the low ionization potential of the aza substit uent, which leads to a strong reduction of the positive charge on the terminal donor in the excited state.