A luminescent open-shell organic radical with high chemical stability was synthesized. (3,5-Dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM) was photoluminescent under various conditions. Fluorescence quantum yields of 0.03, 0.26, and 0.81 (the highest value reported for a stable organic radical) were obtained in chloroform, in poly(methyl methacrylate) film at room temperature, and in an EPA matrix (diethyl ether:isopentane:ethanol) at 77 K, respectively. The photostability of PyBTM is up to 115 times higher than that of the tris(2,4,6-trichlorophenyl)methyl radical, a previously reported luminescent radical. The pyridine moiety of PyBTM acts as a proton coordination site, thereby allowing for control of the electronic and optical properties of the radical by protonation and deprotonation.

Novel luminescent radicals, Br 2 PyBTM and F 2 PyBTM were synthesized and their structures, spectroscopic properties, photostability, and electronic structures were compared with those of Cl 2 PyBTM. Br 2 -PyBTM showed the highest photostability and F 2 PyBTM displayed the highest photoluminescence quantum yield of the three radicals.

A gold(I) complex containing an open-shell luminescent (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl (PyBTM) radical was prepared. The complex showed fluorescence centered mainly on the coordinated PyBTM ligand. The photophysical and photochemical properties were positively modulated upon coordination to Au(I); the photoluminescence quantum yield, fluorescence wavelength, and the stability in the photoexcited state all increased.

A rational molecular design for open-shell molecules to enhance their luminescence efficiency was developed. Introduction of fluorine atoms and coordination of gold(i) to PyBTM, a highly stable fluorescent radical containing a pyridyl moiety, synergistically contributed to yield ten times increase of its fluorescence quantum yield (2 → 20%).