Synthesis of donor–acceptor molecules bridged by turned oligopeptides and their photo-induced electron-transfer process

Abstract

Electron donor–acceptor molecules bridged by a β-turned dipeptide were synthesized; donor =p-(dimethylamino)phenyl, acceptor = 9-anthryl, and β-turned dipeptide = Pro-Xaa.†; ¹H NMR data indicated that freedom of the molecule in solution was moderately restricted by intramolecular hydrogen bonding; the order of the rigidity follows the sequence: trans-form (in the CO–Pro amido bond) of the molecule 1 with D-Pro-L-Xaa > cis-form of 1, trans-form of the diastereoisomeric 2 with L-Pro-L-Xaa > cis-form of 2. Fluorescence data showed that intramolecular photo-induced electron transfer occurred in an acetonitrile solution of the molecule. In the process, the electron should move more slowly in the more conformationally restricted conformer, trans-1, than in cis-1 and trans-2.