Raman Activities of Cyano-Ester Quinoidal Oligothiophenes Reveal Their Diradical Character and the Proximity of the Low-Lying Double Exciton State

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