Necessary and Sufficient Condition for Organic Room‐Temperature Phosphorescence from Host–Guest Doped Crystalline Systems

Abstract

were behind the development of novel highly active research areas in organic electronics and photonics, namely: thermally activated delayed fluorescence (TADF) [1] and organic long-lived luminescence, that includes organic roomtemperature phosphorescence (RTP) [2,3] and organic long-persistent luminescence (LPL). [4] Each of these distinct luminescence phenomena originates from complex emission mechanisms enabled by the crossover between various types of excited states with different electron spin multiplicities. [5][6][7][8][9][10][11][12] Despite the manipulation of excited states energy levels is a difficult task, suitable emitting compounds have been engineered for each luminescence subtype, [13][14][15][16][17][18][19][20][21] as well as for co-existing emissions (e.g., simultaneous RTP and TADF). [22][23][24] To date, the best performance materials in each class exhibit emission lifetimes that are lower than 1 µs for TADF molecules, [25] and that can last up, after ceasing the excitation, to a few tens of seconds for RTP materials [26] and to an hour for LPL systems. [4] In terms of materials engineering, most of the suitable emitting molecules combine electron-donor (D) and Controlling and predicting the long-lived room-temperature phosphorescence (RTP) from organic materials are the next challenges to address for the realization of new efficient organic RTP systems. Here, a new approach is developed to reach these objectives by considering host-guest doped crystals, as well-suited model systems in that they allow the comprehensive understanding of synergetic structural interactions between crystalline host matrices and emitting guest molecules, one of the key parameters to understand the correlation between the solid-state organization and crystal RTP performances. Two series of σ-conjugated donor/acceptor (D-σ-A) carbazolebased matrices and isomeric 1H-benzo[f]indole-based dopants are designed, capable of exploring a wide variety of conformations thanks to large rotational degrees of freedom provided by the σ-conjugation. By correlating the results of single-crystal X-ray diffraction analysis and photoluminescence properties, a necessary and sufficient condition for RTP is established that paves the way for the development of new long-lived RTP host-guest doped systems.

Light‐Induced Electron Transfer Toward On/Off Room Temperature Phosphorescence in Two Photochromic Coordination Polymers

“…[ 1–6 ] Many efforts have been contributed to the design of materials with highly efficient RTP via the strategy of enhancing the intersystem crossing (ISC) rate and stabilizing triplet excitons for long‐lived lifetimes, especially in the molecular crystalline materials due to their highly ordered structures. [ 7–12 ] In this respect, many families of crystalline systems, including one‐component organic crystals, [ 13–16 ] hybrid halides, [ 17–20 ] and metal‐organic complexes, [ 21–24 ] have been developed with efficiently persistent emission and prolonged lifetimes. More recently, stimuli‐responsive RTP complexes are attracting more attention for their importance in constructing smart luminescent switches and developing optical logical gates.…”

Functionalized tails influence photoluminescence emissions for advanced applications in the fiel of time-resolved information input and erasure

“…4A′′ and B′′). 10 Thus, Cz–C 7 –COOH demonstrates superior RTP performance to Cz–C 8 –Tu, which is probably due to a stable excited triplet state (T 1 *) formed via the π–π interactions between the Cz rings. 19,53…”

“…4A 0 0 and B 0 0 ). 10 Thus, Cz-C 7 -COOH demonstrates superior RTP performance to Cz-C 8 -Tu, which is probably due to a stable excited triplet state (T 1 *) formed via the p-p interactions between the Cz rings. 19,53 Overall, depending on the engineering of the functional tails, molecular packing models can be finely tuned to realize ultralong RTP emissions, and this method is a simple but effective way to study the function-structure relationship.…”

“…[1][2][3] Until now, for the purpose of realizing efficient ORTP emissions from the point of view of material processing methodology, building a rigid molecular environment via various approaches, such as crystal engineering, 4,5 host-guest doping, 6 polymerization 7 and supramolecular assembly 8 have been extensively explored and numerous representative works were published, especially during the last five years. For instances, Attias 9,10 and Chen groups [11][12][13] reported host-guest doped systems in D-s-A molecules, where the host-guest dopant is formed by the cooperative electronic effect of different crystal structures, and molecular electronic properties only change slightly. In these reports, the relationship between structure and property is discussed.…”

“…For this reason, finding a new chemical structure is not only a promising way to develop high performance optical materials but can also supplement more information to gain a deep awareness of the internal emission mechanism at a molecular level. 7,16,17 Generally, apart from being a way to enhance the ISC efficiency by establishing strong intramolecular interactions to decrease the energy gap (DE ST ) between singlet and triplet states, 26,40 two factors have been employed to aid the understanding of structure-function relationships to fabricate ultralong RTP materials: (1) the number of intermolecular interactions, 10,30 a classical strategy where the introduction of highly polarized functional groups highly favours greater intermolecular interaction numbers, 49 thus forcing the molecular packing into a more tight pattern, which is able to avoid triplet excitons from nonradiative energy decay as much as possible, one that can also prevent the penetration of exciton quenchers (O 2 , H 2 O) from external surroundings; 17,50 (2) the type of intermolecular interactions, as we know, different types of intermolecular interactions make different contributions to the RTP emission efficiency, for instance, multiple H-bonding 7,25,51 benefits the solidifying of molecular packing and decreases nonradiative energy decay. By introducing different substituents, Li et al 26 achieved multi-stage photo responsive properties by regulating the molecular conformation and packing structure of the aggregated state of triphenylethylene derivatives.…”