Nature of the absorption bands of pyrylocyanines.2. Influence of t-Bu, Ph and Th ring substituents

The effects of t-Bu, Ph and Th substituents on the absorption spectra of alpha-and gamma-pyrylocyanines and their heteroanalogues have been investigated using experimental and quantum-chemical methods. It has been found that changes in the position of the absorption band depend on the electronegativity of the ring heteroatom (O, S, N CH3), polymethine length, and the position of the bond between the chain and the end group. In the case of dye molecules, the effect of two substituents was additive, in contrast to the corresponding salts of the intial heterocycles. An explanation for the significant shifts in the absorption maximum of the thienylcyanines has been presented.