Siloxy Group-Induced Highly Efficient Room Temperature Phosphorescence with Long Lifetime

Abstract

The design and development of organic phosphors that exhibit efficient emission at room temperature but do not contain precious metals such as iridium and platinum have attracted increasing attention. We report herein highly efficient green phosphorescence-emitting 1,4-dibenzoyl-2,5-bis(siloxy)benzene crystals in air at room temperature. Remarkable luminescence quantum yields of 0.46 to 0.64 and long lifetimes ranging from 76.0 to 98.3 ms were observed. Xray diffraction analysis of the single crystals revealed that there were several intermolecular interactions causing suppression of intramolecular motion, thereby minimizing nonradiative decay of the triplet excited state. Comparison with the corresponding 2,5-bis(dimethylphenylsilylmethyl) and 2,5-bis(trimethylsilyl) derivatives revealed that the siloxy groups are essential for efficient room temperature phosphorescence. Density functional calculations suggested that σ−n conjugation was operative in the siloxy moieties. Electron spin resonance measurement indicated that the radiative process included generation of the triplet diradical species, whose electron distribution was very similar to that of naphthalene. The present study largely expands the possibilities for the molecular design of precious metal-and halogen-free organic phosphors exhibiting efficient room temperature phosphorescence.

Prolonging Ultralong Organic Phosphorescence Lifetime to 2.5 s through Confining Rotation in Molecular Rotor

“…The well‐known way to suppress the nonradiative decay is reducing the temperature, which can provide a rigid molecular environment to boost UOP, whereas their application fields are extremely limited due to the harsh conditions of low temperature. As a preferable choice, the UOP became more intriguing under ambient condition recently, and has been achieved by suppressing the nonradiative decay of triplet excitons via several strategies, such as host–guest doping, crystallization, the construction of metal–organic frameworks, polymerization, H‐aggregation, and other methods . In other words, the restriction of the molecular motions such as rotation, vibration, etc.…”

Polymorphic Pure Organic Luminogens with Through‐Space Conjugation and Persistent Room‐Temperature Phosphorescence

“…So far,r esearchers have tried to promote the spin-orbit coupling (SOC) and subsequent intersystem crossing( ISC) through incorporation of carbonyl groups (C=O), halogens, and heteroatoms. [17,[20][21][22]31] At the same time, several other approaches, including radical-ion pairs, [32] s-n conjugation, [33] crystallization, [24,[34][35][36][37] embeddingi n ar igid matrix, [9,[38][39][40] Ha ggregation, [8,31,41] metal-organic frameworks or organic-inorganic perovskites, [42][43][44] have been proposed to stabilize the triplet excitons as am eans to achieve efficient p-RTP luminogens.…”

Roles of Localized Electronic Structures Caused by π Degeneracy Due to Highly Symmetric Heavy Atom‐Free Conjugated Molecular Crystals Leading to Efficient Persistent Room‐Temperature Phosphorescence

“…[12] In the host-guest molecular materials, the highly rigid short conjugated matrix could suppress k q (RT) caused by endothermic triplet-triplet energy transfer from guest to host molecules and effectively protect triplet excited species from oxygen, contributing substantially to the appearance of persistent RTP. [56] However, for most heavy atom-free conjugated molecular crystals with persistent RTP, [9,[14][15][16]25,26,[46][47][48][49][50][51] the quantum yield of persistent RTP (Φ p (RT)) of conjugated molecular crystals with an RTP lifetime approaching to 1 s is often a few percent or less. [56] However, for most heavy atom-free conjugated molecular crystals with persistent RTP, [9,[14][15][16]25,26,[46][47][48][49][50][51] the quantum yield of persistent RTP (Φ p (RT)) of conjugated molecular crystals with an RTP lifetime approaching to 1 s is often a few percent or less.…”

“…[11][12][13][14][15][16][17] Because heavy atom-free molecules with T 1 with strong ππ* characteristics have very small k p , [18] RTP from such conjugated structures exhibits persistent emission characteristics. [32][33][34][35][36][37][38] Except for a few reports before 2000, [9,10] persistent RTP characteristics under ambient conditions have been observed recently from heavy atom-free isolated conjugated molecules doped in a highly rigid amorphous host [12,20,21,[39][40][41] and crystalline host, [42,43] carbon nanodots, [13,[22][23][24]44,45] heavy atom-free aromatic crystals, [14][15][16]25,26,[46][47][48][49][50][51][52] metal-organic frameworks, [17,53] and nonconventional luminogens. [19] Therefore, these materials are potentially useful for a variety of applic...…”