SYNTHESIS AND CRYSTAL-STRUCTURES OF 3 RIGIDLY LINKED DONOR-ACCEPTOR SYSTEMS DESIGNED TO TEST THE EFFECT OF BRIDGE CONFIGURATION ON THE DYNAMICS OF LONG-RANGE INTRAMOLECULAR ELECTRON-TRANSFER PROCESSES

The synthesis and single crystal X-ray structures of three rigid bichromophoric systems are described, namely the dicyanovinyl derivatives of 7,12-dimethoxydodecahydro-1,4:6,13-dimethanopentacen-15-one, 3, 8,13-dimethoxyhexadecahydro-1,4:5,16:6,17:7, 14-tetramethanohexacen-17-one, 4 and 6,11-dimethoxy-4b,12b-dimethyldodecahydro-4,13:5,12-dimethano-2H-indeno-[5',6':3',4']cyclobuta[1',2':3,4]cyclobuta[1,2-b]anthracen-2-one 5. Compounds 3 and 4 were synthesized from dimethanonaphthacene 8 via Diels-Alder reaction with tetrachlorodimethoxycyclopentadiene 9 (in the case of 3) and via successive Diels-Alder reactions, firstly with hexachlorocyclopentadiene, 14, and then with 9, in the case of 4. The synthesis of 5 was achieved through ring expansion of the dichloroketene [2 + 2] cycloadduct formed from 21. Differences in the rates of photoinduced intramolecular electron transfer in 3-5, compared with those for 1 and 2, are rationalized in terms of the differing configurations of the hydrocarbon bridges in these systems, as revealed by X-ray crystallography.