Intermolecular Electronic Coupling of Organic Units for Efficient Persistent Room‐Temperature Phosphorescence

Abstract

Although persistent room‐temperature phosphorescence (RTP) emission has been observed for a few pure crystalline organic molecules, there is no consistent mechanism and no universal design strategy for organic persistent RTP (pRTP) materials. A new mechanism for pRTP is presented, based on combining the advantages of different excited‐state configurations in coupled intermolecular units, which may be applicable to a wide range of organic molecules. By following this mechanism, we have developed a successful design strategy to obtain bright pRTP by utilizing a heavy halogen atom to further increase the intersystem crossing rate of the coupled units. RTP with a remarkably long lifetime of 0.28 s and a very high quantum efficiency of 5 % was thus obtained under ambient conditions. This strategy represents an important step in the understanding of organic pRTP emission.

Efficient Room‐Temperature Phosphorescence of a Solid‐State Supramolecule Enhanced by Cucurbit[6]uril

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Efficient emission of purely organic room-temperature phosphorescence (RTP) is of great significant for potential application in optoelectronics and photobiology. [4] So far, most of organic RTPm aterials are organometallic complexes.C onsidering their high cost and restriction in resources,t he development of purely organic (metal-free) phosphorescent materials are of great concern.[5] However,p hosphorescence of purely organic molecules are fairly weak owing to their inefficient spin-orbit coupling, [6] hence massive efforts have been devoted to achieving efficient RTPb yd eveloping new methods,s uch as special design of structure, [7] embedding into proper matrix [8] and careful crystallization. The chromophore bromophenyl-methyl-pyridinium (PY) with different counterions as guests displayvarious phosphorescence quantum yields from 0.4 %t o2 4.1 %.

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“…Furthermore,ifthe phosphorescence of PYCl/CB [6] was originated from the external interaction between portal carbonyl moiety of CB [6] and the pyridine ring hydrogen atoms of PYCl, the replacing of CB [6] to smaller homolog CB [5] should have little effect on the phosphorescence.H owever,P YCl/CB [5] had aw eak blue-purple emission peak at 420 nm with fairly low efficiency (3.2 %) and short lifetime (8.52 ms), quite different from that of PYCl/CB [6] (Figures S17a,b,S20d,i and Table S1). [27] PYCl/CB [7] had aw eak phosphorescent emission peak at 482 nm with al ong lifetime of 2.20 ms in solid (Figures S17c,d, S20e,j and Table S1). [21,26] Therefore,weconcluded that the host-guest interaction between CB [6] and PYCl, but not external interaction, was responsible for the promotion of phosphorescent properties.M oreover,w er eplaced host CB- [6] with larger homolog CB [7] to identify the size effect on the boosting for phosphorescence.T he 7.3 diameter of CB [7] was enough to bond PYCl which was supported by the large chemical shift of PYCl ( Figure S19).…”

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

“…4, the S 0  → T 1 transition configurations are very similar to that of S 0  → S 1 in TADF molecules of DMAC-DPS and Spiro-CN , containing both high HOMO (H) → LUMO (L) components; there are also apparent component overlap with the same transition configurations between S 0  → S n (n = 1 and 2) and S 0  → T 1 in HLCT molecules of MADa and TPA-NZP ; in OURTP molecules ( DPhCzT and DCzPhP ), still the same transition configurations can be observed between S 0  → S 1 and S 0  → T n (n = 4, 6, 8, 10, or 13) within the critical energy gap of 0.37 eV. Considering the El-Sayed rule that predicts accelerated ISC by vibronic interactions between ( π , π *) and ( n , π *) states 19 , the same transition configuration component of the two excited states indicates their overlapped excitation features, which should be crucial for the enhanced ISC through these allowed transformation channels; and it can be expected that the more overlapped the transition configurations are, the more facile the exciton transformation will be through this channel 36, 37 .…”

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...…”