The conversion of light to chemical energy is performed routinely in nature (photosynthesis) but there are no synthetic chemical systems that can match this efficiency. A molecule in an excited electronic state (L*) has the potential to use this energy to perform a chemical reaction e.g. photoinduced electron transfer (PET) with an electron acceptor (A) or donor, or to achieve electronic energy transfer (EET) to a sensitiser molecule (S). In the absence of either of these deactivation processes, the electronic energy will be released as light (luminescence) as the system returns to its ground state. Therefore, these three deactivation pathways are always in competition. If one can better understand the factors that favour a particular deactivation pathway over others then it becomes possible to design systems that can efficiently achieve light to energy conversion.

Naphthalene and anthracene and their derivatives comprise a class of particularly well studied aromatic molecules that may undergo either PET or EET while in their excited state. The efficiency of luminescence quenching can be greatly enhanced by covalent attachment of a functional group that can undergo either PET or EET with the aromatic luminophore as shown above for the bifunctional macrocyclic Zn(II) complex ( see E. G. Moore, P. V. Bernhardt, A. Pigliucci, M. J. Riley and E. Vauthey, J. Phys. Chem. A, 2003, 107, 8396)