where the bra/ket notation refers to integration with respect to r h and r e . The exciton size, defined in this way, is a transferable measure that provides insight into charge transfer between isolated molecules, covalently bonded donor-acceptor systems, as well as large conjugated π-systems. Purely local excitations generally have a d exc of 4 Å or less, where anything above this value indicates at least partial CT character. In addition we will utilise the absolute mean electron-hole separation