Symmetry Breaking and Hydrogen Bonding in Phthalimide Compounds Enable Efficient Room-Temperature Circularly...

The development of purely organic chiral room temperature phosphorescence (RTP) emitters is attracting more and more attention. However, the key parameters governing the polarized luminescence process remain difficult to predict and rationalize since the phosphorescence emission is rarely obtained in solution, hampering any structure-relationship studies. To address this challenge, we report here the synthesis and chiroptical properties of a new family of metal-free phosphorescent emitters based on phthalimide derivatives. Breaking symmetry of the phthalimide units and using intra- and intermolecular hydrogen bonding enable the obtention of circularly polarized (CP) RTP in solution with g_lum of up to 5 × 10^-3. Interestingly, our investigations demonstrate the intricate role of hydrogen bonding interactions in modulating triplet state generation through the mixing of singlet and triplet states of different nature, i.e., n-π* and π-π*, in the excited state, which is a crucial parameter for achieving intense CP-RTP. These results bring additional molecular design guidelines to reach CP-RTP in solution and additionally offer new insights into the subtle relationships between excited states of different spin multiplicity to reach higher CP phosphorescence intensity.