A Rigid Chlorin-Naphthalene Diimide Conjugate. A Possible New Noncovalent Electron Transfer Model System

Described in this paper is the synthesis and study of a rigid "coplanar" noncovalent electron-transfer model system. This putative noncovalent complex juxtaposes a novel donor (chlorin) and acceptor (naphthalene diimide) via a three-point hydrogen bonding interaction (CDCl(3), K(a) = 364 +/- 47 M(-)(1)). It was studied by steady state fluorescence, time-resolved luminescence, and transient absorption methods. The results of the studies are consistent with (1) forward intraensemble electron transfer (ET) taking place rapidly following photoexcitation of the chlorin donor at 575 nm (k(ET) = 7.6 x 10(8) s(-)(1); DeltaG(cs) approximately -457 mV; Phi = 0.91) and (2) back electron transfer occurring even more rapidly.