Structure-Aromaticity-Spectroscopy Relationship in Conjugated Polymers

In this study, an effort has been made to analyze the aromaticity of oligomers of benzene and thiophene, with and without linkers using Nucleus-Independent Chemical Shift (NICS) as a descriptor, and their relation with HOMO-LUMO gap, reorganization energy and excitation energy. Thus, calculations have been performed to develop structure-aromaticity-spectroscopy relationship. Although the inter-relationship between geometry and aromaticity has been extensively discussed in the literature, the present study provides pointers about relationship between aromaticity, conjugation, and spectroscopic properties. Benzene and thiophene-based oligomers have been chosen for the study comprising of vinyl and ethynyl linkers along with the α-linked benzene and thiophene oligomers as model systems. The results show that both HOMO-LUMO gaps and excitation energies exhibit linear relationship with inverse of the NICS values, indicating the possible existence of the structure-aromaticity-π-conjugation-spectroscopy relationship.