SYNTHESIS, ELECTROCHEMISTRY AND AB-INITIO MOLECULAR-ORBITAL CALCULATIONS ON SOME NORBORNANE-FUSED AND BICYCLO[2.2.2]OCTANE-FUSED 5,12-BIS(DICYANOMETHYLIDENE)NAPHTHALENE SYSTEMS

A series of norbornane- and bicycle [2.2.2]octane-fused tetracyanonaph thoquinodimethane (benzo-TCNQ) derivatives, 4, 6, 8, 10 and 12 has bee n synthesized. Cyclic voltammetry measurements revealed two One-electr on reduction waves for the benzo-TCNQ systems 4, 8 and 10 which posses s either a cyclobutane or a norbornane moiety fused to the quinonoid r ing, but a single (presumably two-electron) reduction wave for 6 add 1 2 which possess a bicyclo[2.2.2]octane group fused to the quinonoid ri ng. The benzo-TCNQ systems were found to be potent electron accepters. The results of(U)HF/3-21G calculations carried out on representative benzo-TCNQ derivatives suggest that steric interactions between the qu inonoid ring and its adjacent fused alicyclic group are largely respon sible for the observed decrease in the electron affinities along the s eries: 8 > 4 > 6, The MO calculations further suggest that LUMO energi es of neutral TCNQ derivatives are qualitatively reliable predictors o f electron affinities, The calculated (gas phase) internal reorganizat ion energies, lambda(i), for the benzo-TCNQ systems are ca. 54 kJ mol( -1) and are comparable to that calculated for the dicyanovinyl (DCV) s ystem, 27, The similarity between the lambda(i) values for the benzo-T CNQ systems and 27, together with the experimental finding that benzo- TCNQ systems are reduced at ca. 1.7 V less negative potentials than 27 , should make the norbornane- and bicyclo[2.2.2] octane-benzo-TCNQ sys tems superior to the DCV moiety as acceptor chromophores in giant mult ichromophoric systems.