Highly-Photostable Emissive Thienyl-containing Tris(2,4,6-trichlorophenyl)methyl Radicals

Abstract

Luminescent organic radicals are among the most promising materials for spintronics, upconversion, red and near infrared (NIR) organic light-emitting diodes suffering from the spin-statistics limitations. However, the number of emissive radicals applied in electronic devices is limited, and their design principles are still under discussion. Here we designed, synthesized and studied a series of tris(2,4,6-trichlorophenyl)methyl (TTM) radicals with thiophene-based donors. The radicals were synthesized via cross-coupling reaction of convenient monobromo-substituted TTM precursor followed by the proton elimination and oxidation. Our DFT calculations and experimental data indicate the HOMO energy of the donor strongly affects the radical emission properties. The radical with the highest optical gap demonstrated deep red electroluminescence and photoluminescence with quantum yield up to 12%. The photostability of radicals was found to increase dramatically with substitution, and, according to the proposed mechanistic picture, the spin density on chlorine atoms, energy and lifetime of the lowest excited state, D1, control the photodegradation rate. Our results not only extend the pool of the luminescence radicals but also provide clear physical and chemical insights into their fundamental structure-properties relations and may serve as a basis for future molecular design of highly stable and emissive radicals.