Synthesis and analysis of UV/visible spectra of carbocyanine dimer models

Dimers 1 and 2, having a pair of the carbocyanine moieties connected at the meso-positions by an –O–Ph–O– or –S–Ph–S– bridge, were prepared. Their UV/visible spectra displayed a first absorption maxima at ca. 750 nm, a second absorption maxima at ca. 800 nm and a shoulder at ca. 850 nm. Since MOPAC calculations indicated that the configuration of the dimers was folded, but twisted, strong H-type coupling together with weaker J-type coupling takes place along the longer axis of the dimers. The UV/visible spectra of the dimers were characterized by a split in the long wavelength absorption of the corresponding carbocyanine chromophore into a more intense blue shift and a less intense red shift. Remarkably, the dimers showed greater sensitivity to solvent polarity than the monomers 3 and 4.