Ultrafast triplet formation in thionated perylene diimides

Perylene diimides (PDIs) are versatile n-type materials showing great promise in a number of optoelectronic applications. While the singlet manifold of PDI can be readily populated, triplet excited states are only accessible through complex multistep energy cascades or bimolecular sensitization. In this work, we have synthesized a series of thionated PDIs that display rapid intersystem crossing to triplet states. Significantly, the thionated PDIs are synthesized in one step from the parent compound using commercially available Lawesson's reagent. Electrochemical and steady state optical absorption measurements show that the electron affinity and ionization potentials can be systematically tuned through successive sulfur atom substitution. Thin-film optical absorption measurements show how the number and regiochemistry of the thiocarbonyl groups influence χ-χ interactions in the solid state. Ultrafast transient absorption spectroscopy reveals rapid triplet formation that is independent of the degree of thionation, highlighting this approach as a facile means of accessing the triplet manifold of PDI.