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

The effects of t-Bu, Ph and Th substituents on the absorption spectra of al pha- and gamma-pyrylocyanines and their heteroanalogues have been investiga ted using experimental and quantum-chemical methods. It has been found that changes in the position of the absorption band depend on the electronegati vity of the ring heteroatom (O, S, N CH3), polymethine length, and the posi tion of the bond between the chain and the end group. In the case of dye mo lecules, the effect of two substituents was additive, in contrast to the co rresponding salts of the initial heterocycles. An explanation for the signi ficant shifts in the absorption maximum of the thienylcyanines has been pre sented. (C) 2000 Elsevier Science Ltd. All rights reserved.