Evolution of the Nature of Excitons and Electronic Couplings in Hybrid 2D Perovskites as a Function of Organic Cation π-Conjugation

2D perovskites have attracted much attention, due to their organic-inorganic hybrid nature and layered configuration. Multi-quantum-well structures then generally form since the inorganic frameworks and organic spacers have typically well-separated frontier energy levels. Here, it is focused on the opposite picture where wavefunction hybridization occurs between the frontier orbitals of the two components. Such a hybridization emerges upon tuning the strength of electronic coupling between the inorganic and organic layers. A series of model diammonium organic spacers is theoretically designed with varying extent of pi-conjugation along their backbones. Wavefunction hybridization is realized in a Dion-Jacobson 2D perovskite combining PbI4 inorganic layers with anthracene-bis(ethan-1-ammonium) organic spacers. An analysis of the electronic band structures points to electronic couplings as high as 30-40 meV between the organic and inorganic components. Such couplings can lead to the formation of interfacial hybrid excitons or to the appearance of Dexter-type energy transfer conducive to phosphorescence in the organic layers. Overall, the results highlight that a variety of excitonic behaviors could be observed by tuning the degree of conjugation of the organic cations and the structural proximity and electronic couplings between the organic and inorganic constituents.