Insight into the Excited States in Monomers and π-Stacked Dimers of Azulene-Fused Acenes: ADC(2) and TD-DFT Studies.

Abstract

Charge transfer (CT) states in polycyclic aromatic hydrocarbons play crucial roles in determining their electronic properties and their potential applications in organic electronics. In this work, we investigate the nature of the excited states in monomers and π-stacked dimers of azulene-fused naphthalene and anthracene systems, focusing on the interplay between structure and excited-state properties. Four different isomers for azulene-fused naphthalene (NapAz-A, NapAz-B, NapAz-C, and NapAz-D) and anthracene (AntAz-A, AntAz-B, AntAz-C, and AntAz-D) are considered. The excited-state studies are performed at the SCS-ADC(2) level and at the TD-DFT level using CAM-B3LYP, SCS-ωB2GP-PLYP, and SCS-RSX-QIDH functionals. For the monomers, the SCS-ADC(2) results reveal that states with CT characters are different in naphthalene- and anthracene-based systems. In π-stacked dimers, a few of the excited states are of the charge resonance (CR) type in NapAz-A, NapAz-B, and NapAz-C and the intermolecular CT type in NapAz-D. Similarly, AntAz-A, AntAz-B, and AntAz-D have some CR type excited states, whereas the AntAz-C isomer has intramolecular CT type excited states. Overall, among the three DFT functionals considered, CAM-B3LYP has been found to reproduce well the SCS-ADC(2) excited results in both monomers and π-stacked dimers.