Energy Levels and Color of Polymethine Dyes

Publisher Website
Google Scholar
Abstract
The secular determinant for the energy levels of the unsaturation electrons of a polymethine dye is discussed in both HLSP and LCAO approximations. The roots of the secular determinant, which were obtained in the preceding paper by Herzfeld, are applied to a discussion of the longest wave‐length electronic band of symmetrical and unsymmetrical polymethines. The LCAO approximation gives good numerical values for the dependence of both the transition energy and oscillator strength on the length of the polymethine chain in symmetrical dyes, but cannot handle the questions which depend sensitively on a small difference between the groups attached to the two nitrogen atoms at the extreme ends of the chain. Although the HLSP method yields correct qualitative results for symmetrical dyes, it does not give good numerical values. The HLSP method, however, is sensitive to a difference between the two ends of the dye molecule and affords a simple explanation for a number of properties in which unsymmetrical dyes differ from symmetrical ones.

This publication has 11 references indexed in Scilit: