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) π-π*) 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 π-localized RTP. In the model system of N-substituted naphthalimides (NNIs), the relatively large energy gap between the NNI-localized (1) π-π* and (3) π-π* 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.

Materials with both fluorescence and room-temperature phosphorescence (RTP) can be useful in the field of optoelectronics. Here we present a general strategy, taking advantage of carbonyl compounds, which have been known to possess efficient intersystem crossing with high triplet state yield, as well as a strongly fluorescent intramolecular charge-transfer (ICT) state, to produce materials with both fluorescence and RTP at the same time, or dual-emission. In the presented model systems, in order to generate a suitable ICT state, Lewis acid binding to aromatic ketone derivatives has been proved to be a viable method. We have selected AlCl3, BCl3, BF3, and GdCl3 as binding Lewis acids, in that they exhibit sufficiently strong binding affinity toward the aromatic ketone derivatives to afford stable complexes and yet do not possess low-lying electronic transitions vs the ligands. We have successfully observed dual-emission from these designed complexes in polymers, which act to suppress competitive thermal decay at room temperature. One of the complexes is particularly interesting as it is dual-emissive in the crystalline state. Single-crystal XRD reveals that the molecule forms multiple hydrogen bonds with its neighbors in crystals, which may significantly enhance the rigidity of the environment.

Single-component materials with both fluorescence and room-temperature phosphorescence (RTP) are useful for ratiometric sensing and imaging applications. On the basis of a general design principle, an amino-substituted benzophenone is covalently incorporated into waterborne polyurethanes (WPU) and results in fluorescence and RTP single-component dual-emissive materials (SDMs). At different aminobenzophenone concentrations, the statistical, thermal, and optical properties of these SDMs are characterized. Despite their similar thermal behaviors, the luminescence properties as a function of the chromophore concentration are quite different: increasing concentrations led to progressively narrowed singlet-triplet energy gaps. The tunability of fluorescence and RTP via chromophore concentration is explained by a previously proposed model, polymerization-enhanced intersystem crossing (PEX). The proposal of PEX is based on Kasha's molecular exciton theory with a specific application in polymeric systems, where the polymerization of luminophores results in excitonic coupling and enhanced forward and reverse intersystem crossing. The mechanism of PEX is also examined by theoretical calculations for the WPU system. It is found that the presence of K1 aggregates indeed enhances the crossover from singlet excited states to triplet ones.

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