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A P Monkman - One of the best experts on this subject based on the ideXlab platform.
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photophysics of an asymmetric donor acceptor donor tadf molecule and reinterpretation of aggregation induced tadf emission in these materials
Journal of Physical Chemistry C, 2017Co-Authors: Murat Aydemir, Chengjian Chen, Martin R Bryce, Zhenguo Chi, A P MonkmanAbstract:We report an in-depth photophysical investigation of an asymmetric donor–acceptor–donor′ (D–A–D′) thermally activated delayed fluorescence (TADF) molecule (4-(9H-carbazol-9-yl)phenyl)(4-(10H-phenothiazin-10-yl)phenyl)sulfone and compare its photophysical properties to the parent symmetric D–A–D and D′–A–D′ molecules. These D–A–D type small molecules all show strong TADF. The work reveals how the relative orientations of D–A (D′–A) moieties favor reverse intersystem crossing (rISC) by forming stable charge transfer (CT) States. The key requirement for the efficient TADF emitters is to achieve a very small CT-local Triplet State Energy splitting, which is shown to be complex in the asymmetric molecule. Throughout the investigations, we show that in the asymmetric D–A–D′ system, even though ECT (D–A) > ECT (D′–A), no evidence of Energy transfer from D–A to A–D′ is observed, nor from excited D to D′. This is ascribed to the near orthogonality of the D and D′ units and the very strong decoupling of the electro...
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Photophysics of an Asymmetric Donor–Acceptor–Donor′ TADF Molecule and Reinterpretation of Aggregation-Induced TADF Emission in These Materials
2017Co-Authors: Murat Aydemir, Chengjian Chen, Martin R Bryce, Zhenguo Chi, A P MonkmanAbstract:We report an in-depth photophysical investigation of an asymmetric donor–acceptor–donor′ (D–A–D′) thermally activated delayed fluorescence (TADF) molecule (4-(9H-carbazol-9-yl)phenyl)(4-(10H-phenothiazin-10-yl)phenyl)sulfone and compare its photophysical properties to the parent symmetric D–A–D and D′–A–D′ molecules. These D–A–D type small molecules all show strong TADF. The work reveals how the relative orientations of D–A (D′–A) moieties favor reverse intersystem crossing (rISC) by forming stable charge transfer (CT) States. The key requirement for the efficient TADF emitters is to achieve a very small CT-local Triplet State Energy splitting, which is shown to be complex in the asymmetric molecule. Throughout the investigations, we show that in the asymmetric D–A–D′ system, even though ECT (D–A) > ECT (D′–A), no evidence of Energy transfer from D–A to A–D′ is observed, nor from excited D to D′. This is ascribed to the near orthogonality of the D and D′ units and the very strong decoupling of the electrons on the D and A in the CT State. In addition, the possibility of aggregation-induced TADF (AI-TADF) is examined and shown to be a manifestation of solvatochromism in these particular molecules
Reinhard Schmidt - One of the best experts on this subject based on the ideXlab platform.
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mechanism of photosensitized generation of singlet oxygen during oxygen quenching of Triplet States and the general dependence of the rate constants and efficiencies of o2 1σg o2 1δg and o2 3σg formation on sensitizer Triplet State Energy and oxidation potential
Journal of Physical Chemistry A, 2003Co-Authors: Claude Schweitzer, Zahra Mehrdad, Astrid Noll, Erichwalter Grabner, Reinhard SchmidtAbstract:Rate constants of photosensitized generation of O2(1Σg+), O2(1Δg), and O2(3Σg-) have been determined for a series of ππ* Triplet sensitizers with strongly varying oxidation potential (Eox), Triplet Energy (ET), and molecular structure, in CCl4. We demonstrate that one common dependence on Eox and ET successfully describes these rate constants for the molecules studied here and also for all previously investigated ππ* sensitizers, independently of molecular structure or any other parameter. Photosensitized singlet oxygen generation during O2 quenching of ππ* Triplet States can be generally described by a mechanism involving the successive formation of excited noncharge transfer (nCT) encounter complexes and partial charge transfer (pCT) exciplexes of singlet and Triplet multiplicity 1,3(T13Σ), following interaction of O2(3Σg-) with the Triplet excited sensitizer. Both 1,3(T13Σ) nCT and pCT complexes decay by internal conversion (ic) to yield O2(1Σg+), O2(1Δg), and O2(3Σg-) and the sensitizer ground State. ...
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Triplet State Energy dependence of the competitive formation of o2 1σ g o2 1δg and o2 3σ g in the sensitization of o2 by Triplet States
Chemical Physics Letters, 1994Co-Authors: M Bodesheim, Matthias Schutz, Reinhard SchmidtAbstract:Abstract Time-resolved emission spectroscopy of O 2 ( 1 Σ + g ) and O 2 ( 1 Δ g ) in CCl 4 was used to determine the rate constant k 1 Σ , k 1 Δ and k 3 Σ , of the Triplet State (T 1 ) sensitized formation of the 1 Σ + g , 1 Δ g and 3 Σ − g States of O 2 . 13 sensitizers of Triplet energies 140⩽ E T ⩽309 kJ mol − were investigated. The data are analyzed with respect to the excess energies Δ E of the corresponding deactivation paths. They follow a common dependence on Δ E . The rate constants reach maximum values around Δ E =60 kJ mol − and decrease subsequently exponentially with increasing Δ E . This dependence on Δ E is much weaker than expected by previous theories and is explained by the intermediacy of exciplexes 1,3 (T 1 3 Σ). Above Δ E =240 kJ mol − k 3 Σ increases strongly with Δ E .
Claude Picard - One of the best experts on this subject based on the ideXlab platform.
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quantum chemistry based interpretations on the lowest Triplet State of luminescent lanthanides complexes part 2 influence of the electrostatic interactions on the Triplet State Energy of terbium complexes
Journal of Molecular Structure-theochem, 2005Co-Authors: Fabien Gutierrez, Christine Tedeschi, Laurent Maron, Jeanpierre Daudey, Joelle Azema, Pierre Tisnes, Claude Picard, Romuald PoteauAbstract:Abstract In part I of this series, we have focused our attention on a theoretical interpretation of the luminescent properties of some recently synthetized lanthanide–hydroxamate complexes (LnL 3 stoichiometry, with L − =[CO–N(R)O] − ). Following the Jablonski diagram, and considering that sensitization of lanthanide ions from S 1 does not seem to occur frequently, the efficiency of the luminescence of terbium complexes is essentially related to the energetic position of the first excited Triplet State (T 1 ). Due to the size of the complexes, we have used DFT (density functional theory) and TDDFT (time-dependent density functional theory) based approaches, which allowed us to make calculations on the full systems. The purpose of the present paper is to present new results and interpretations obtained through a modelization of the 1:3 complexes, either by replacing two bidentate hydroxamate ligands by a chlorine atom, or with an even simpler model in which the lanthanide atom itself is replaced by a sodium atom. At first, we have checked that this quite crude modelization is essentially in agreement with the calculations on the full complex, both for the structural properties and for the nature and qualitative position of the T 1 State. In the last part, we propose to explain the variation of S 0 –T 1 excitation energies in terms of electrostatic interactions between the metal center and the ligands, related to the variation of the M–L distances. Concluding remarks concern the different possibilities of performing a quick and reliable screening of luminescent properties of new lanthanide complexes, which was the chief goal of the present work. Considering one strategy, i.e. the replacement of TbL 3 by NaL, we propose, prior to chemical synthesis, the methyl 1-hydroxypyridin-2-one-5 carboxylate as a relevant ligand for an efficient luminescence of terbium complexes.
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quantum chemistry based interpretations on the lowest Triplet State of luminescent lanthanides complexes part 1 relation between the Triplet State Energy of hydroxamate complexes and their luminescence properties
Dalton Transactions, 2004Co-Authors: Fabien Gutierrez, Christine Tedeschi, Laurent Maron, Jeanpierre Daudey, Romuald Poteau, Joelle Azema, Pierre Tisnes, Claude PicardAbstract:In this paper, we evaluate the potential use of theoretical calculations to obtain an Energy scale of the lowest ligand-centred Triplet excited State in luminescent terbium(III) complexes. In these complexes, non-radiative deactivation of the terbium emitting State via a back-Energy transfer process (T1 ← Tb(5D4)) is a common quenching process. Consequently the prediction of the Energy gap between these two excited States should be useful for programming highly luminescent TbIII systems. We report on a strategy based upon experimental and theoretical investigations of the excited State properties of a series of four simple aromatic hydroxamate ligands coordinated to TbIII and GdIII ions. By using previously reported crystallographic data, the structural and energies properties of these systems were investigated in the ground and first excited Triplet States at the density functional theory (DFT) level of calculations. Our theoretical results are consistent with a Triplet excited State T1 which is localised on one ligand only and whose the Energy level is independent of the lanthanide ion nature (TbIII, GdIII). A good agreement between the calculated adiabatic transition energies and experimental data derived from emission spectra is obtained when a corrective term is considered. These satisfactory results are an indication that this type of modelling can lead to discriminate in terms of the position of the lowest ligand Triplet Energy level the best antenna among a family of chromophoric compounds. In addition this theoretical approach has provided indications that the difference between the adiabatic transition energies of all the investigated complexes can be mainly explained by metal–ligand electrostatic interactions. The influence of the number of antennae on the quantum yield and the luminescence lifetime is discussed.
Murat Aydemir - One of the best experts on this subject based on the ideXlab platform.
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photophysics of an asymmetric donor acceptor donor tadf molecule and reinterpretation of aggregation induced tadf emission in these materials
Journal of Physical Chemistry C, 2017Co-Authors: Murat Aydemir, Chengjian Chen, Martin R Bryce, Zhenguo Chi, A P MonkmanAbstract:We report an in-depth photophysical investigation of an asymmetric donor–acceptor–donor′ (D–A–D′) thermally activated delayed fluorescence (TADF) molecule (4-(9H-carbazol-9-yl)phenyl)(4-(10H-phenothiazin-10-yl)phenyl)sulfone and compare its photophysical properties to the parent symmetric D–A–D and D′–A–D′ molecules. These D–A–D type small molecules all show strong TADF. The work reveals how the relative orientations of D–A (D′–A) moieties favor reverse intersystem crossing (rISC) by forming stable charge transfer (CT) States. The key requirement for the efficient TADF emitters is to achieve a very small CT-local Triplet State Energy splitting, which is shown to be complex in the asymmetric molecule. Throughout the investigations, we show that in the asymmetric D–A–D′ system, even though ECT (D–A) > ECT (D′–A), no evidence of Energy transfer from D–A to A–D′ is observed, nor from excited D to D′. This is ascribed to the near orthogonality of the D and D′ units and the very strong decoupling of the electro...
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Photophysics of an Asymmetric Donor–Acceptor–Donor′ TADF Molecule and Reinterpretation of Aggregation-Induced TADF Emission in These Materials
2017Co-Authors: Murat Aydemir, Chengjian Chen, Martin R Bryce, Zhenguo Chi, A P MonkmanAbstract:We report an in-depth photophysical investigation of an asymmetric donor–acceptor–donor′ (D–A–D′) thermally activated delayed fluorescence (TADF) molecule (4-(9H-carbazol-9-yl)phenyl)(4-(10H-phenothiazin-10-yl)phenyl)sulfone and compare its photophysical properties to the parent symmetric D–A–D and D′–A–D′ molecules. These D–A–D type small molecules all show strong TADF. The work reveals how the relative orientations of D–A (D′–A) moieties favor reverse intersystem crossing (rISC) by forming stable charge transfer (CT) States. The key requirement for the efficient TADF emitters is to achieve a very small CT-local Triplet State Energy splitting, which is shown to be complex in the asymmetric molecule. Throughout the investigations, we show that in the asymmetric D–A–D′ system, even though ECT (D–A) > ECT (D′–A), no evidence of Energy transfer from D–A to A–D′ is observed, nor from excited D to D′. This is ascribed to the near orthogonality of the D and D′ units and the very strong decoupling of the electrons on the D and A in the CT State. In addition, the possibility of aggregation-induced TADF (AI-TADF) is examined and shown to be a manifestation of solvatochromism in these particular molecules
Bingfu Lei - One of the best experts on this subject based on the ideXlab platform.
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multiemissive room temperature phosphorescent carbon dots znal 2 o 4 composites by inorganic defect Triplet State Energy transfer
ACS Applied Materials & Interfaces, 2021Co-Authors: Zhijian Song, Yingliang Liu, Xiaomin Lin, Zhishan Zhou, Xuejie Zhang, Jianle Zhuang, Bingfu LeiAbstract:Room-temperature phosphorescence (RTP) with carbon dots (CDs) can be exploited further if the mechanism of trap-State-mediated Triplet-State Energy transfer is understood and controlled. Herein, we developed an in situ calcination method for the preparation of a CDs@ZnAl2O4 composite material that exhibits unique UV and visible light-excitable ultra-broad-band RTP. The ZnAl2O4 matrix can protect the Triplet emissions of CDs by the confinement effect and spin-orbit coupling. In addition, benefitting from the efficient Energy transfer between the inorganic trap State and the Triplet State of CDs, the special yellow to red RTP of CDs@ZnAl2O4 composites can be realized. A slow-decaying phosphorescence at 570 nm with a lifetime of 1.05 s and a fast-decaying phosphorescence at 400 nm with a lifetime of 0.41 s were observed with UV irradiation of 290 nm, which originated from the surface and core Triplet States of CDs, respectively. Based on the unique RTP performance, anti-counterfeiting and information encryption were successfully realized using the CDs@ZnAl2O4 composites with LED light or UV light.
