Davydov splitting and singlet fission in excitonically coupled pentacene dimersDedicated to Professor Fritz Wasgestian on the occasion of his 85th birthday.Electronic supplementary information (ESI) available: Supplemental Information includes synthetic protocols, details about the analysis of photophysical data, 50 figures and X-ray crystallographic data for 1a (cif), 1d (cif), 4b (cif), and 4c (cif). CCDC 1839936, 1839935, 1839934 and 1839933. For ESI and crystallographic data in CIF or other

Singlet fission (SF) allows two charges to be generated from the absorption of a single photon and is, therefore, potentially transformative toward improving solar energy conversion. Key to the present study of SF is the design of pentacene dimers featuring a xanthene linker that strictly places two pentacene chromophores in a rigid arrangement and, in turn, enforces efficient, intramolecular π-overlap that mimics interactions typically found in condensed state ( e.g. , solids, films, etc. ). Inter-chromophore communication ensures Davydov splitting, which plays an unprecedented role toward achieving SF in pentacene dimers. Transient absorption measurements document that intramolecular SF evolves upon excitation into the lower Davydov bands to form a correlated triplet pair at cryogenic temperature. At room temperature, the two spin-correlated triplets, one per pentacene moiety within the dimers, are electronically coupled to an excimer state. The presented results are transferable to a broad range of acene morphologies including aggregates, crystals, and films. Singlet fission (SF) allows two charges to be generated from the absorption of a single photon and is, therefore, potentially trans-formative toward improving solar energy conversion.