Photophysical properties of mixed-ligand complexes (ArS)2ZnPhen with interligand charge-transfer excited states: influence of substituents in the arylthiolate ligand

Galin, A.M.; Razskazovsky, Yu. V.; Melnikov, Mikhail Ya.

doi:10.1016/1010-6030(93)85082-j

Cited by 11 publications

(5 citation statements)

References 7 publications

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“…Only a few phosphorescent Zn(II) complexes have been reported in the literature, including a hemicage Zn bipyridyl complex ZnL 3 (L 3 = m ‐(bpy(C 2 H 4 )) 3 C 6 H 3 (CH 3 ) 3 , with bpy=2,2′‐bipyridine), [20] Zn porphyrins [21–23] and several representatives of a broader class of [Zn(thiolate) 2 (diimine)] complexes [24–30] . Very recently, ultra‐long lifetimes in the millisecond regime were reported for cyclic (alkyl)(amino)carbene (cAAC) complexes of Zn(II) halides at 77 K and shown to stem from ligand‐centered triplet states [31] .…”

Section: Introductionmentioning

confidence: 99%

“…[19] Only a few phosphorescent Zn(II) complexes have been reported in the literature, including a hemicage Zn bipyridyl complex ZnL 3 (L 3 = m-(bpy(C 2 H 4 )) 3 C 6 H 3 (CH 3 ) 3 , with bpy = 2,2'bipyridine), [20] Zn porphyrins [21][22][23] and several representatives of a broader class of [Zn(thiolate) 2 (diimine)] complexes. [24][25][26][27][28][29][30] Very recently, ultra-long lifetimes in the millisecond regime were reported for cyclic (alkyl)(amino)carbene (cAAC) complexes of Zn(II) halides at 77 K and shown to stem from ligand-centered triplet states. [31] While ISC and phosphorescence of Zn(II) porphyrins are known to be vibronically induced, [32] the underlying mechanisms operative in the Zn(II) diimine dithiolates are not well understood despite some very sophisticated and detailed studies conducted by Crosby and coworkers.…”

Section: Introductionmentioning

confidence: 99%

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Revisiting Ligand‐to‐Ligand Charge Transfer Phosphorescence Emission from Zinc(II) Diimine Bis‐Thiolate Complexes: It is Actually Thermally Activated Delayed Fluorescence

et al. 2022

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In this work we revisit and re-evaluate the photophysical behavior of the prototypical complex [Zn(SC 6 H 4 -4-R) 2 (phen)] as the most in-depth studied type of Zn(II)-based triplet state emitters. Previous reports suggest population of ligand-toligand charge transfer (LLCT) states via phenanthroline localized ππ* states, with an energy barrier between the 3 ππ* and the bk; 1/3 LLCT states requiring thermal activation. Besides very weak prompt fluorescence, the dominant radiative mechanism was attributed to phosphorescence. Our photophysical studies, including temperature-dependent quantum yield determination and time-resolved luminescence measurements, reveal a high radiative rate constant k r = 3.5 × 10 5 s À 1 at room temperature and suggest thermally activated luminescence as the major emission path. High-level DFT/MRCI calculations confirm this assignment and provide deeper insight into the excited-state kinetics, including rate constants for the (reverse) intersystem crossing processes. Thus, our study demonstrates that further optimization of the photophysical properties of this type of Zn(II) triplet exciton emitter bears great potential for future application in devices.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Revisiting Ligand‐to‐Ligand Charge Transfer Phosphorescence Emission from Zinc(II) Diimine Bis‐Thiolate Complexes: It is Actually Thermally Activated Delayed Fluorescence

et al. 2022

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“…Therefore, the propensity of MLCT states is low in Zn(II). Formerly investigated zinc complexes mainly showed prompt fluorescence and only a few were reported to be phosphorescent. − A recent re-investigation of the photophysical behavior of zinc(II) diimine bis-thiolate complexes revealed that their room-temperature LLCT emission actually shows TADF characteristics . With regard to lighting applications, Zn(II) complexes were mostly employed as fluorescent emitters or hosts for fluorescent and phosphorescent dopants. − The growing interest in new TADF-based OLED emitters strongly promoted research on Zn(II) emitters.…”

Section: Introductionmentioning

confidence: 99%

Finding Design Principles of OLED Emitters through Theoretical Investigations of Zn(II) Carbene Complexes

2022

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In this work, Zn(II) carbene complexes carrying a dianionic 1,2-dithiolbenzene (dtb) or 1,2-diolbenzene (dob) ligand were investigated regarding their suitability as organic light-emitting diode (OLED) emitter. For the optimization of the complexes, density functional-based methods were used and frequency analyses verified the obtained structures as minima. All calculations were carried out including a polarizable continuum model to mimic solvent−solute interactions. Multireference configuration interaction methods were used to determine excitation energies, spin-orbit couplings, and luminescence properties. Rate constants of spinallowed and spin-forbidden transitions were calculated according to a Fermi golden rule expression. Using carbene ligands with varying σ-donor and π-acceptor strengths, the luminescence is found to be tunable from yellow to orange/red to deep red/nearinfrared. The calculated intersystem crossing (ISC) time constants indicate thermally activated delayed fluorescence (TADF) to be the main decay channel. In contrast to many d 10 coinage metal complexes, a parallel orientation of dtb or dob and the carbene ligand is found to be highly favorable. For the complexes with a cyclic (alkyl)(amino) carbene (CAAC) or cyclic (amino)(aryl) carbene (CAArC) ligand, the S 1 and T 1 states have ligand-to-ligand charge-transfer (LLCT) character and are energetically close. The complex with a classical N-heterocyclic carbene (NHC) ligand has S 1 and T 1 states with mixed ligand-to-metal charge-transfer (LMCT)/LLCT character and is a very rare example in which the zinc ion contributes to the excitation.

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“…Triplet excitons, which account for 75% of all generated excitons upon recombination of the charge carriers in the OLED, are therefore preferentially harvested by thermally activated delayed fluorescence (TADF) rather than phosphorescence. , In contrast, exchange interaction and hence the singlet–triplet energy splitting are typically large for LC ππ* excitations. While 1 LC states of some zinc complexes are brightly fluorescent, , 3 LC phosphorescence is rare and observed at low temperatures only − as radiative rate constants of 3 LC states are very small and competitive nonradiative deactivation processes slow down when the sample is cooled. In OLEDs, 3 LC states of the dopant can mediate the intersystem crossing (ISC) between 1 CT and 3 CT states if they are energetically close but they can equally well act as excitation energy sinks if they constitute the lowest-lying excited state of the dopant.…”

Section: Introductionmentioning

confidence: 99%

Polarity-Tunable Luminescence and Intersystem Crossing of a Zinc(II) Diimine Dithiolate Complex

Putscher,

Marian

2023

J. Phys. Chem. A

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Combined density functional theory and multireference configuration interaction methods including spin−orbit interactions have been employed to investigate the photophysical properties and deactivation pathways of a zinc diimine dithiolate complex involving the phenanthroline derivative bathocuproine and the dianionic dithiosquarate as chelating ligands. Zn(batho)(dtsq) is one of the few luminescent zinc complexes for which triplet emission had been reported in the solid state [Gronlund, P. et al. Inorg. Chim. Acta 1995, 234, 13−18]. Because of the high dipole moment of the complex in the electronic ground state, ligand-toligand charge-transfer (LLCT) states experience strong hypsochromic shifts in polar media, while ligand-centered (LC) states are nearly unaffected. Rate constants for the thermally activated upconversion of the T LLCT population to the S LLCT state are promising due to a small singlet−triplet energy gap and the participation of the sulfur in the electronic excitation, but the T LLCT state is not the lowest-lying excited triplet state in ethanol solution. In addition to the T LLCT electronic structure, T LC(batho) ′ and T LC(dtsq) ππ* excitations form minima on the T 1 potential energy surface. The S LLCT luminescence is expected to be quenched at the nanosecond time scale by the dark T LC(dtsq) ππ* state. Moreover, a T LC(dtsq) σπ* state has been identified, which leads to degradation of the compound. In mildly polar media, the dark triplet LC states are energetically inaccessible and the lowest excited singlet and triplet states clearly exhibit an LLCT character. However, their mutual spin−orbit coupling is reduced to the extent that reverse intersystem crossing is not very likely at room temperature. While Zn(diimine)(dithiolate) complexes continue to be perceived as an interesting substance class with potential application as emitters in electroluminescent devices, the particular Zn(batho)(dtsq) complex is not considered suitable for that purpose.

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Photophysical properties of mixed-ligand complexes (ArS)2ZnPhen with interligand charge-transfer excited states: influence of substituents in the arylthiolate ligand

Cited by 11 publications

References 7 publications

Revisiting Ligand‐to‐Ligand Charge Transfer Phosphorescence Emission from Zinc(II) Diimine Bis‐Thiolate Complexes: It is Actually Thermally Activated Delayed Fluorescence

Revisiting Ligand‐to‐Ligand Charge Transfer Phosphorescence Emission from Zinc(II) Diimine Bis‐Thiolate Complexes: It is Actually Thermally Activated Delayed Fluorescence

Finding Design Principles of OLED Emitters through Theoretical Investigations of Zn(II) Carbene Complexes

Polarity-Tunable Luminescence and Intersystem Crossing of a Zinc(II) Diimine Dithiolate Complex

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