SPECTROSCOPIC STUDIES OF THIATRIMETHINE, PENTAMETHINE AND HEPTAMETHINE CYANINE DYES .1. STRUCTURE OF THIATRIMETHINE, PENTAMETHINE AND HEPTAMETHINE CYANINE DYES IN SOLUTIONS STUDIED BY NMR

The 400 MHz H-1 NMR spectra of thiatri-, penta- and heptamethine cyanine dyes in methylene chloride (or chloroform) solutions has been measured in order to provide new insight into their solution structure. Assignments of H-1 signals arising from the 1Hs in the chromophoric parts have been made by measurements of the nuclear Overhauser effect (NOE) and H-1-H-1 chemical shift-correlated spectroscopy (COSY). Chemical shifts and coupling constants of the obtained spectra suggest that the methine chains of the central conjugated systems of the cyanine dyes investigated take extended all-trans forms and the CC bonds in the chains have bond orders of 1.5. This investigation has been required for the structural analysis of the cyanine dyes in Langmuir-Blodgett films.