Conformation-Induced Excimer Formation in Covalently Linked Dimer of Azulene-Fused Anthracene

Excimers are important excited-state homodimeric complexes affecting excited-state processes such as symmetry-breaking charge separation (SB-CS) and singlet fission (SF). Their formation is influenced by factors such as the solvent environment, spatial orientation, and distance between the chromophores. Our study uses MP2 and ADC(2) methods to explore excimer formation in a specific conformer of covalently linked azulene-fused anthracenes, out of two conformers, M1 and M2. In conformer M1, the azulene units are oriented toward each other, leading to excimer formation in the S₁ state. This is confirmed by the orbital overlap of the azulene units and the charge transfer (CT) character of the S₁ state. In contrast, in conformer M2, the azulene rings are oriented away from each other, and this results in minimal geometric changes in the excited-state geometry, keeping the CT features intact.