Potential singlet fission chromophores of azulene-containing tetracene analogues: a theoretical study

Singlet fission (SF) is a promising photophysical process for improving the photoelectric conversion efficiency in photovoltaic devices. However, the limited number of SF chromophores hinders basic research and practical applications. Here a series of azulene-containing tetracene and [4]helicene analogues were designed, and further modified by nitrogen insertion and the attachment of substituents, to expand the library of SF-capable molecules. The relationship between their molecular structures and SF feasibility was analyzed based on the diradical character, the frontier molecular orbital analysis and SF relevant excited state energies. The calculated results show that the incorporation of an azulene unit efficiently reduces E(T1), and the insertion of a nitrogen atom and the attachment of electron-donating/-withdrawing groups optimize the SF performance of compound B4, to give the balance between the fulfillment of the SF energetic matching conditions and SF sensitizers. These findings help to design new SF-capable molecules and offer insights into the relationship between SF properties and azulene-containing polycyclic aromatic hydrocarbons (PAHs). Azulene-containing tetracene analogues were designed and theoretically evaluated for extending the library of singlet fission sensitizers.