Spectroscopic studies of a near-infrared absorbing pH sensitive aminodienone-carbocyanine dye system

Synthetic red and near-infrared absorbing dyes may be used as probe molecules in a large number of applications. Dyes exhibiting spectral changes with hydrogen ion concentration are useful as pH probes. Those dyes which have their absorption and fluorescence maxima in the long wavelength region of the visible spectral region are specially valuable because of decreased interference and semiconductor laser applications. In this paper we have evaluated an aminodienone dyes 1 which demostrates pH dependent absorption and fluorescence spectra as well as solvent polarity dependence. In organic solvents the long wavelength absorption band of the dye is in the reduced interference region. The absorption maximum is at 535 nm in neutral or alkaline solutions in methanol. The absorption spectra undergo a strong bathochromic shift in the presence of acids (lambda(max) = 709 nm) with a concomitant change in the fluorescence spectra. This pH sensitive dye was found to be specially especially useful for organic solvents. The analytical utility of this and similar near-infrared absorbing dyes is discussed.