Quinoidal oligothiophenes have received considerable attention as interesting platforms
with remarkable amphoteric redox behavior associated with their diradical character increasing
with the conjugation lengths. In this work, we considered a family of quinoidal oligothiophenes
bearing cyano-ester terminal groups and characterized them by UV-Vis-NIR absorption and Raman
spectroscopy measurements at different excitation wavelengths. The experimental investigation is
complemented by quantum-chemical studies to assess the quality of computed density functional
theory (DFT) ground state structures and their influence on predicted Raman intensities. In addition,
resonance conditions with the optically active HOMO→LUMO transition as well as with the more
elusive state dominated by the doubly excited HOMO,HOMO→LUMO,LUMO configuration, are
determined with DFT-MRCI calculations and their contributions to Raman activity enhancement are
discussed in terms of computed vibrational Huang–Rhys (HR) factors
