EVIDENCE FOR SPIRO-CONJUGATION IN PERPENDICULARLY-LINKED PENTAMETHINESTREPTOCYANINE DIMERS

Perpendicularly-linked pentamethinestreptocyanine dimers (1) in which the two cyanine moieties are linked at the center carbon atoms of the methine chains were prepared. The absorption spectra of 1 in solution showed two peaks at 446 and 406 nm, which are attributed to the splitt ing of the HOMO levels through spiro-conjugation between the two cyani ne moieties, as calculated from the INDO/S-CI method. The reduction po tential of 1 positively shifted with respect to that of the correspond ing monomer (2). The oxidation polarogram of 1 showed two waves, with the first potential negatively shifting compared to that of 2.