On the photophysics of nanographene – investigation of functionalized hexa-peri-hexabenzocoronenes as model systems

In the current study, we report on hexa-peri-hexabenzocoronenes (HBCs) as a representative model for nanographene. To this end, we synthesized a family of functionalized HBCs and investigated the impact of the substituents on the π-extended system of the HBCs. DFT and TD-DFT calculations suggested a charge transfer character, which intensifies as the electron density withdrawing effects of the substituents (–M-effect) increase. Unambiguous corroboration of the charge transfer character in the case of the NO2-substituents was realized with steady-state absorption and fluorescence experiments, which focused on the dependencies on solvent polarity and temperature featuring. Going beyond HBCs with NO2-substituents time-correlated single photon counting, femtosecond and nanosecond transient absorption spectroscopy unveil long-lived singlet and triplet excited states. As a complement, we performed electrochemical and spectroelectrochemical measurements. These were carried out to shed light onto the nature of functionalized HBCs as electron acceptors and/or donors, on one hand, and their corresponding spectroscopic signatures, on the other hand. All of the aforementioned enabled intermolecular charge separation assays with, for example, suitable electron acceptors by steady-state and time-resolved spectroscopies