ortho-Heterofluorene perylenediimides: synthesis, photophysical, and exciton dynamic properties.

Previous studies suggest the perylenediimide (PDI) triplet excited state (T) have been accessible only through bimolecular sensitization, the internal heavy-atom effect or a sophisticated cascade of nonradiative processes. Here, we designed heavy-atom-free PDIs to prompt the T ← S intersystem crossing (ISC) by introducing electron donating heterofluorene groups at the head positions of the electron-deficient PDI core. We obtained relatively high ISC efficiency up to 92% yield. Furthermore, promptly generated PDI triplets can sensitize the molecular oxygen quantitatively to yield O, with singlet oxygen generation efficiencies (Φ) near to unity. These results further suggest that the ISC process of PDIs can be enhanced through the intramolecular charge transfer (ICT) interaction, providing guidelines for developing triplet-generating PDIs and related rylene diimides for optoelectronic applications.