Tunable Charge Transfer In Functionalised Betainoïd Pyridinium‐Benzimidazole Scaffolds: Computational and Experimental Insights Into Optical Properties

Donor–acceptor systems are promising systems for applications in optoelectronics. The zwitterionic nature of betainoid pyridinium compounds allows a unique set of tunable electronic properties, but their rationalization remains challenging. Herein, the optical properties of a series of five derivatives are studied experimentally and computationally to unveil and rationalize their distinctive intramolecular charge transfer properties. These compounds consist of 4‐functionalised‐pyridine with H, tert ‐butyl, dimethylamino, trifluoroborate and oxo linked through their nitrogen atom to benzimidazole at its C2 position ( 1 –5 respectively). The transitions responsible for the absorption and emission properties observed experimentally are investigated using density functional theory and time dependent‐DFT. Calculated absorption energies systematically match the experimental λ max , while the prediction of emission energy seems to be less straightforward. By use of the molecular orbitals, charge distribution evolution, change in electric dipole moment, and calculated vertical excitations, we are able to rationalize structure‐properties relations involved in these transitions. This study allows us to gain insights into the optoelectronic properties of a series of unique donor–acceptor systems using computationally cost‐effective methods.