The El-Sayed’s rule analogy enables long-lived room temperature phosphorescence in twisted biphenyls

Wu, Bingze; Su, Hao; Cheng, Aoyuan; Zhang, Xuepeng; Wang, Tao; Zhang, Guoqing

doi:10.1016/j.xcrp.2022.101245

Cited by 14 publications

(14 citation statements)

References 44 publications

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“…The latter rule suggests that the change in spin multiplicity is intriguingly coupled to a change in orbital symmetry in order to conserve the total angular momentum in the exciton transfer process. In fact, excited states with different wave function spatial symmetry leading to large SOC was well illustrated in several earlier studies. − ,− This essentially leads to a large SOC for S 1 → T 2 ISC in Az-CHS and, thereby, resulting in a very high S 1 ( n π*) → T 2 (ππ*) ISC of k ISC ∼10 9 s –1 (see SOC and ISC rates from Figure ). Importantly, an in-plane vibration with mode-frequency similar to ω eff of 1407 cm –1 associated with a large Huang–Rhys factor is identified to drive the exciton transfer.…”

Section: Resultssupporting

confidence: 67%

Molecular-Scale Design of Azulene-Based Triplet Photosensitizers: Insights from Time-Dependent Optimally Tuned Range-Separated Hybrid

Debnath,

Ahmed,

Manna

2023

J. Phys. Chem. B

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Metal-free triplet photosensitizers are ubiquitous in photocatalysis, photodynamic therapy, photovoltaics, and so forth. Their photosensitization efficiency strongly depends on the ability of the low-lying excited spin-triplet to be populated through intersystem crossing. Small singlet–triplet gaps and considerable spin–orbit coupling between the excited spin-singlet and spin-triplet facilitate efficient intersystem crossing. Azulene (Az), a classic example of Anti-Kasha’s blue emitter with considerable fluorescence quantum yield, holds great promise because of its chemical stability, rich electronic properties, and high structural rigidity. Here, we provide computationally modeled Az-derived photosensitizers, namely, Az-CHO and Az-CHS, implementing polarization consistent time-dependent optimally tuned range-separated hybrid. Calculations reveal energetic reordering of low-lying ππ* and nπ* singlet states between Az-CHO and Az-CHS and, thereby, rendering the latter to a nonfluorescent one. Importantly, a small singlet–triplet gap and large spin–orbit coupling for Az-CHX with X = O and S produce remarkably high intersystem crossing rates. Furthermore, strong nonadiabatic coupling between the S 1(nπ*) and S 2(ππ*) in Az-CHS due to substantially smaller energy gap causes enhanced S 1 population via fast internal conversion. These research findings provide new insights into the development of functional Az and or related heavy-atom-free small organic molecule-based triplet photosensitizers.

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Section: Resultssupporting

confidence: 67%

Molecular-Scale Design of Azulene-Based Triplet Photosensitizers: Insights from Time-Dependent Optimally Tuned Range-Separated Hybrid

Debnath,

Ahmed,

Manna

2023

J. Phys. Chem. B

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“…In contrast, harvesting triplet excitons via room-temperature phosphorescence (RTP) from the lowest triplet (T1) state to the ground (S0) state has become an attractive alternative approach. Recently, many design principles that rely on intra- and/or intermolecular interactions, − aggregates, , host–guest chemistry, excited-state engineering, halogen effect, ,, heavy chalcogen atom effect, and orthogonal donor–acceptor (D–A), ,,, biaryl, and donor–spacer–acceptor ,,− geometries have been developed. Nevertheless, a handful of reports comprising chemical modification, mechanical force, , conformational switching, intramolecular CT, regioisomeric effect on the excited state, and change of host matrices have recently observed simultaneous TADF and RTP. ,− Despite these achievements, structure–property correlation in simultaneous thermally enhanced phosphorescence (TEP) and its impact on TADF remain unclear due to fast internal conversion and the supersensitive nature of the triplet excitons.…”

Section: Introductionmentioning

confidence: 99%

Modulation of Delayed Fluorescence Guided by Conformational Effect-Mediated Thermally Enhanced Phosphorescence in Phenothiazines–Quinoline–Cl Conjugates

Dey,

Pal,

Upadhyay

et al. 2023

J. Phys. Chem. B

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Triplet energy harvesting via thermally activated delayed fluorescence (TADF) from pure organic systems has attracted great attention in organic lightemitting diodes, sensing, and photocatalysis. However, the realization of thermally enhanced phosphorescence (TEP)-guided efficient TADF with a high rate of reverse intersystem crossing (k RISC ) still needs to be discovered. Herein, we report two phenothiazine−quinoline conjugates (P2QC, P2QMC) comprising two phenothiazine donors covalently attached to the chlorine-substituted quinolinyl acceptor. Spectroscopic analysis in conjunction with quantum chemistry calculations reveals that TEP in P2QC originated due to slow internal conversion from higher-lying triplet to lowest triplet (T2′ → T1′) of the quasi-axial (QA) conformer and TADF (k RISC = 1.44 × 10 8 s −1 ) originated from the quasi-equatorial (QE) conformer caused by a low singlet−triplet gap (ΔE S1−T1 = 0.11 eV) and triplet energy transfer from QA to QE owing to the degenerate ground state of the conformers. In contrast, TADF (k RISC = 0.74 × 10 8 s −1 ) and dual phosphorescence under ambient conditions are observed in P2QMC. This study provides a sustainable guideline for developing efficient TADF emitters via conformation effects and energy transfer mechanisms.

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“…In Figure S25, it is shown that the HOMO and HOMO–1 have degenerated consisting of lone pair (n) electrons of C atoms of carbene and N atoms of pyridine, together with d electrons of Cu 3 and π electrons in the N–C–N moieties in the five-member rings; while the electron density of LUMO delocalizes on Cu 3 (s, p orbital) and N–C–N (π* orbital) moieties. Thus, the different electronic configurations would possess effective SOC channels between the low-lying excited states. , …”

Section: Resultsmentioning

confidence: 99%

“…Thus, the different electronic configurations would possess effective SOC channels between the low-lying excited states. 74,75 Furthermore, the phosphorescence wavelength was calculated by the energy difference between T 1 and the relaxation energy at the singlet energy surface (S 0 ). Indeed, at the PBE0/ def2-SVP theoretical level, the calculated phosphorescence wavelength is 459 nm, fitting well with the experimental value (456 nm).…”

Section: ■ Introductionmentioning

confidence: 99%

High-Efficiency Pure Blue Circularly Polarized Phosphorescence from Chiral N-Heterocyclic-Carbene-Stabilized Copper(I) Clusters

Ma,

Si,

et al. 2023

J. Am. Chem. Soc.

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Circularly polarized luminescence (CPL) materials have attracted considerable attention for their promising applications in encryption, chiral sensing, and three-dimensional (3D) displays. However, the preparation of high-efficiency, pure blue CPL materials remains challenging. In this study, we reported an enantiomeric pair of triangle copper(I) clusters (R/S -Cu 3 ) rigidified by employing chiral N-heterocyclic carbene (NHC) ligands with two pyridine-functionalized wingtips. These chiral clusters emitted pure blue phosphorescence that overlapped with that of the commercial blue phosphor having Commission Internationale de l’Eclairage (CIE) chromaticity coordinates of (0.14, 0.10), and the films exhibited an unprecedented photoluminescence quantum yield (PLQY) of ∼70.0%. Additionally, the solutions showed very bright circularly polarized phosphorescence (CPP) with a dissymmetry factor of ±2.1 × 10–3. The excellent solubility and photostability endowed these pure-blue-emitting chiral clusters with promising applications as pure blue CPP inks for 3D printing white objects, such as precise-atomic-enlarged models of metal clusters and a lovely white stereoscopic “rabbit”. The intricate mechanism underlying blue phosphorescence in this small cluster and across various states is elucidated through a comprehensive approach that integrates thorough analysis of luminescence properties, controlled experiments, and theoretical calculations. For the first time, we propose that the dominant high-energy emission center is constituted by delocalized hybrid orbitals over multiple atomic centers, encompassing both the metal and the coordinated atoms. This challenges stereotypical assumptions that the cluster center solely supports low-energy emissions. This work expands the currently limited range of CPP functional materials and provides a new direction for CPP applications involving NHC-stabilized metal clusters.

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The El-Sayed’s rule analogy enables long-lived room temperature phosphorescence in twisted biphenyls

Cited by 14 publications

References 44 publications

Molecular-Scale Design of Azulene-Based Triplet Photosensitizers: Insights from Time-Dependent Optimally Tuned Range-Separated Hybrid

Molecular-Scale Design of Azulene-Based Triplet Photosensitizers: Insights from Time-Dependent Optimally Tuned Range-Separated Hybrid

Modulation of Delayed Fluorescence Guided by Conformational Effect-Mediated Thermally Enhanced Phosphorescence in Phenothiazines–Quinoline–Cl Conjugates

High-Efficiency Pure Blue Circularly Polarized Phosphorescence from Chiral N-Heterocyclic-Carbene-Stabilized Copper(I) Clusters

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