Versatile Room-Temperature-Phosphorescent Materials Prepared from N-Substituted Naphthalimides: Emission Enhancement and Chemical Conjugation

Purely organic materials with room-temperature phosphorescence (RTP) are currently under intense investigation because of their potential applications in sensing, imaging, and displaying. Inspired by certain organometallic systems, where ligand-localized phosphorescence ((3)pi-pi*) is mediated by ligand-to-metal or metal-to-ligand charge transfer (CT) states, we now show that donor-to-acceptor CT states from the same organic molecule can also mediate pi-localized RTP. In the model system of N-substituted naphthalimides (NNIs), the relatively large energy gap between the NNI-localized 1 pi-pi* and (3)pi-pi* states of the aromatic ring can be bridged by intramolecular CT states when the NNI is chemically modified with an electron donor. These NNI-based RTP materials can be easily conjugated to both synthetic and natural macromolecules, which can be used for RTP microscopy.