Adsorption of organic donor-acceptor molecules on graphene/SiC preserves light-induced charge transfer

Identifying solid substrates that can effectively support donor-acceptor (DA) organic molecules without hindering their intrinsic charge transfer induced by ultraviolet and visible light is crucial for device fabrication and the precise control of photoinduced electric currents. Here, we demonstrate that graphene/SiC(000 $\overline{1}$ ) interfaces preserve the optoelectronic response of three DA molecules: 1-amino-4-nitrobenzene, 1-amino-6-nitro-pyrene, and 1-fluoro-6-methoxy-pyrene. Although adsorption induces a substantial renormalization of the molecular quasiparticle gaps, the corresponding charge-transfer excitation energies exhibit relatively small redshift compared to the gas-phase molecules. This is attributed to the substrate-induced screening that reduces both the quasiparticle gap and the electron-hole binding energy, leading to a partial cancellation in the excitation energy. Additionally, we show that the intramolecular charge-transfer excitons retain their character upon adsorption, suggesting graphene/SiC(000 $\overline{1}$ ) as a suitable platform for stable physisorption of DA chromophores and for enabling time-resolved studies of early-stage charge migration, opening pathways toward molecular optoelectronic architectures with minimal substrate interference.