Rational Molecular Design for Achieving Persistent and Efficient Pure Organic Room-Temperature Phosphorescence

Abstract

Manipulation of the emission properties of pure organic room-temperature phosphors through molecular design is attractive but challenging. Tremendous efforts have been made to modulate their aggregation behaviors to suppress nonradiative decay in order to achieve efficient light emission and long lifetimes. However, success has been limited. To attain such a goal, here we present a rational design principle based on intrinsic molecular-structure engineering. Comprehensive investigations on the molecular orbitals revealed that an excited state with hybrid (n,p*) and (p,p*) configurations in appreciable proportion is desired. Tailoring the aromatic subunits in arylphenones can effectively tune the energy level and the orbital feature of the triplet exciton. Our experimental data reveal that a series of full-color pure organic phosphors with a balanced lifetime (up to 0.23 s) and efficiency (up to 36.0%) can be realized under ambient conditions, demonstrating the validity of our instructive design principle.

Promoting Singlet/triplet Exciton Transformation in Organic Optoelectronic Molecules: Role of Excited State Transition Configuration

“…Although our qualitative method cannot predict the high SOC of S 1  → T 3 suggested by the Dalton calculation, our method succeeds in figuring out efficient SOC channels for exciton transformation. To further identify the proportion of ( n, π * ) configuration ( α n %) of the excited states, Mulliken population analysis (MPA) was performed on the optimized excited state structures with the aid of Multiwfn package 16 . The S 1 of DPhCzT was found to have a high component of 1 ( n, π * ) with α n % of 14.3%, while the T 4 is mainly 3 ( π, π *) with α n % of 0.0%; Such a significant α n % change (Δ α n  = | α n,S1  −  α n,T4 | = 14.3%) suggests the allowed 1 ( n , π * ) →  3 ( n, π * ) transition from S 1 to T 4 according to El-Sayed rule, which is also coincident with the results of our TD-DFT calculation method based on the ground state geometry (S 0 ).…”

“…The SOC values between S 1 and T n were calculated using Dalton package (B3LYP/cc-pVTZ) based on the optimized S 1 state structure. The proportion of 1 ( n, π *) configuration ( α n %) of the excited state was calculated by using Mulliken population analysis (MPA) to identify the n orbital components of the frontier orbitals at the optimized excited state geometries with the aid of Multiwfn package 16 .…”

Intersystem Crossing Mechanisms in the Room Temperature Phosphorescence of Crystalline Organic Compounds

“…A benzophenone derivative (17) fused with a dibenzofuran showed RTP in crystal. 24 TD-DFT calculations for 17 demonstrated that S 1 with a 1 (n, π*) character and T 2 made up by hybridization of 3 (n, π*) and 3 (π, π*) are energetically close enough and capable of SOC. A benzophenone derivative (18) with a carbazole moiety showed RTP in crystal, but it diminished by mechanical griding.…”

“…They also found RTP of diphenylsulfone-dibenzothiophene conjugate (22) and ascribed it to SOC at the sulfonyl oxygen and a small energy gap for S 1 -T 1 transition. 29 Li and coworkers performed TD-DFT calculations on three carbazole derivatives (23,24,25) with regard to their RTP in crystals and pointed out the importance of intermolecular interactions on RTP properties. 30 The N-N interatom distances of dimers in crystals are in the order, 23 (5.53 ¡) < 24 (6.02 ¡) < 25 (6.17 ¡), demonstrating the relationship between the packing looseness and the decreases of RTP lifetime and efficiency.…”

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

“…[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...…”