Kenshiro MATSUDA

Abstract Tris(2,4,6-trichlorophenyl)methyl (TTM) radicals substituted at the C1 and C2 positions of naphthalene were synthesized. The C1 substitution led to a broader photoluminescence (PL) spectrum and a significantly lower PL quantum yield compared to the C2 substitution. Density functional theory calculations suggested that these differences arise from variations in steric effects and the associated molecular conformation in the excited states. Our results emphasize that the bonding position is crucial for controlling the photophysical properties of acene-substituted TTM radicals.

ABSTRACT Luminescent radicals are an emerging class of materials for organic electronics, bioimaging, and quantum applications. Circularly polarized luminescence (CPL) from luminescent radicals with propeller‐type chirality remains challenging because it is difficult to simultaneously achieve high photoluminescence quantum yield (PLQY), high stability, and high racemization barriers. A series of brominated chiral luminescent radicals, CzTTBrM, 2CzTTBrM, and 3CzTTBrM, was obtained by attaching carbazole donors to TTBrM. The donor‐acceptor‐type design induces red to near‐infrared (NIR) emission via charge transfer (CT) excited states with remarkably high PLQY (up to 76%) and high photostability. The new radicals possess high racemization barriers (Δ G ^‡ (353K) = 27.9–29.1 kcal/mol), allowing the isolation of enantiopure compounds at room temperature. The enantiopure radicals exhibit CPL with broad emission across the red to NIR range (650–800 nm) and display B _CPL values (0.76–1.1), nearly one order of magnitude higher than that of TTBrM (B _CPL = 0.16). Moreover, doping these radicals into polystyrene microspheres produces whispering gallery mode (WGM) resonances, marking the first observation of WGM emission from luminescent radicals. This strategy establishes a versatile platform for integrating spin, chirality, and luminescence, offering new opportunities for applications in electroluminescence, bioimaging, and quantum photonics.

Mono carbazole-dendronized tris (2,4,6-trichlorophenyl)methyl (TTM) radicals have recently been reported as bright red emitters, in which second-to fourth-generation dendrons were suggested to induce an increase in photoluminescence quantum yield (PLQY)....

Organic luminescent radicals have emerged as promising open-shell emitters for advanced optoelectronic and sensing applications. Among them, the carbazole-substituted tris(2,4,6-trichlorophenyl)methyl radical (Cz-TTM) exhibits remarkable photostability and emission efficiency compared with the parent TTM radical. Nevertheless, Cz-TTM can be visibly degraded by indoor light irradiation and its photodegradation mechanism is poorly understood. Here, we systematically investigate the photochemical behavior of Cz-TTM in solutions, together with the influence of impurities on the photophysical properties of the compound. We found that emissive and non-emissive impurities are introduced depending on the purification methods and the light irradiation conditions. Impurities cause underestimation of photoluminescence quantum yield through competitive absorption. Photodegradation under continuous irradiation undergoes a multi-step reaction via metastable intermediates, which react with dissolved oxygen upon local excitation of the TTM radical moiety. Quantum-chemical calculations indicate a ring-closure followed by dechlorination within the TTM moiety as the key degradation pathway. The superior photostability of Cz-TTM to TTM originates from its stabilized first excited doublet energy level, which increases the activation energy for ring-closure reaction in Cz-TTM. These combined experimental and theoretical insights reveal the fundamental factors governing the photostability of TTM-type luminescent radicals and offer design principles for next-generation organic luminescent materials.