<scp>MO</scp>‐<scp>LCAO</scp>‐Calculations on polymethines. V. <scp>PPP</scp>‐type calculations and configuration analyses of simple prototype dyes in terms of molecular subsystems

Abstract

Abstract In order to elucidate certain controversies in interpreting the π‐electronic structure of some simple quinone and indigo dyes the Pariser–Parr–Pople SC β,γ ‐wave‐functions have been subjected to configuration analyses. Whereas 2,5‐diamino‐quinone (1) can be excellently represented by coupling of two trimethine‐merocyanine chains, the analogous consideration is less appropriate with bispyrrolindigo (2). In this case the results of the configuration analyses indicate clearly the limited applicability of the Longuet/Higgins–Murrell–method.