Linear and cyclic tetrathiafulvalene-naphthalenediimide donor-acceptor molecules: metal ions-promoted electron transfer

Three linear and one cyclic tetrathiafulvalene-1,4,5,8-naphthalenediimide (TTF-NDI) compounds 1, 2, 3, and 4 were synthesized and studied in the presence of metal ions. Both absorption and electron spin resonance spectroscopic studies clearly indicate that electron transfer occurs from TTF to the NDI unit in the presence of metal ions (Pb(2+) and Sc(3+)) for linear compounds 1 and 2. The mechanism based on the metal ion coordination is proposed for the electron transfer within 1 and 2 after the addition of metal ions. Compound 3 exhibits intramolecular charge-transfer absorption because of the cyclophane framework. Interestingly, intramolecular electron transfer also takes place for 3 after the addition of either Sc(3+) or Pb(2+).