Solid‐State Room‐Temperature Near‐Infrared Photoluminescence of a Stable Organic Radical

Abstract

Dedicated to Prof. Ilhyong Ryu on the occasion of his 70th birthdayLuminescent organic radicals often exhibit unique emission properties when isolated in solution or dispersed in host materials. However, luminescent properties of radicals in the fully aggregated pure solid state have rarely been investigated, especially at room temperature. Herein, a luminescent stable organic radical with a 3-pyridyl moiety, the (2,4-dichloro-3pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (metaPyBTM), was synthesized and characterized. Although the electronic structures and photophysical properties in solution of meta-PyBTM and its analogues are similar, metaPyBTM displays distinct near-infrared photoluminescence in the pure crystalline state at room temperature. The solid-state luminescence properties of metaPyBTM depend strongly on temperature and the degree of aggregation. An external magnetic field also modulates the emission spectrum of metaPyBTM in the moderately aggregated state.

Single-molecule Magnetoluminescence from a Spatially Confined Persistent Diradical Emitter

“…The spacing provided by the THDBA linker is typically 7-8 Å, 43,44 comparable with the shortest intermolecular radical-radical distances observed in crystals of luminescent polychlorinated triarylmethyl radicals. 39 Second, the two radical-spacer bonds are fixed nearly parallel, forcing the two radical units to adopt similar orientations with respect to the linker. Third, meta-connectivity of the aromatic rings in THDBA makes 1 a non-Kekulé diradical, eliminating the contribution of a closed-shell singlet electronic configuration with a quinoid Kekulé structure in the ground state.…”

“…We previously reported unique ML behavior in persistent open-shell molecules, (3,5-dichloro-4-pyridyl)bis (2,4,6-trichlorophenyl)methyl radical (PyBTM) and its derivatives. [35][36][37][38][39][40][41] MFEs were observed when the luminescent radicals were moderately (4-20 wt%) doped into host molecular crystals so that they were partially aggregated (Fig. 1a).…”

Single-molecule Magnetoluminescence from a Spatially Confined Persistent Diradical Emitter

“…The spacing provided by the THDBA linker is typically 7-8 Å, 48,49 comparable with the shortest intermolecular radical-radical distances observed in crystals of luminescent polychlorinated triarylmethyl radicals. 44 Second, the two radical-spacer bonds are fixed nearly parallel, forcing the two radical units to adopt similar orientations with respect to the linker. Third, meta-connectivity of the aromatic rings in 6 / 20…”

“…We previously reported unique ML behavior in persistent open-shell molecules, (3,5-dichloro-4-pyridyl)bis (2,4,6-trichlorophenyl)methyl radical (PyBTM) and its derivatives. [40][41][42][43][44][45][46] MFEs were observed when the luminescent radicals were moderately (4-20 wt%) doped into host molecular crystals so that they were partially aggregated (Fig. 1a).…”

Research Progress on Triarylmethyl Radical-Based High-Efficiency OLED

“…Although the photostability of trisPyM was significantly improved compared with PTM and TTM, its PLQE level was not satisfactory. In the same year, they changed the position of the nitrogen atom through reasonable molecular design and synthesized a new stable organic radical, metaPyBTM [ 104 ], whose nitrogen atom was from para to meta. Although its PLQE and light stability were equivalent to TTM, the radical still showed obvious solid photoluminescence even at room temperature, which provided a new opportunity for organic radicals in the field of optical functions.…”