Abstract
Red luminescence is found in off-white tris(iodoperchlorophenyl)methane (3I-PTMH) crystals which is characterized by a high photoluminescence quantum yield (PLQY 91 %) and color purity (CIE coordinates 0.66, 0.34). The emission originates from the doublet excited state of the neutral radical3I-PTM(R), which is spontaneously formed and becomes embedded in the3I-PTM(H)matrix. The radical defect can also be deliberately introduced into3I-PTM(H)crystals which maintain a high PLQY with up to 4 % radical concentration. The immobilized iodinated radical demonstrates excellent photostability (estimated half-life >1 year under continuous irradiation) and intriguing luminescent lifetime (69 ns). TD-DFT calculations demonstrate that electron-donating iodine atoms accelerate the radiative transition while the rigid halogen-bonded matrix suppresses the nonradiative decay.