1
|
Jodra A, Marazzi M, Frutos LM, García-Iriepa C. Modulating Efficiency and Color of Thermally Activated Delayed Fluorescence by Rationalizing the Substitution Effect. J Chem Theory Comput 2024; 20:4239-4253. [PMID: 38738688 PMCID: PMC11137832 DOI: 10.1021/acs.jctc.4c00009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2024] [Revised: 04/22/2024] [Accepted: 04/25/2024] [Indexed: 05/14/2024]
Abstract
Thermally activated delayed fluorescence (TADF) constitutes the process by which third-generation organic light-emitting diodes (OLEDs) are being designed and produced. Despite several years of trial-and-error attempts, mainly driven by chemical intuition about how to improve a certain aspect of the process, few studies focused on the in-depth description of its two key properties: efficiency of the T1 → S1 intersystem crossing and further S1 → S0 emission. Here, by means of a newly developed theoretical formalism, we propose a systematic rationalization of the substituent effect in a paradigmatic class of OLED compounds, based on phenothiazine-dibenzothiophene-S,S-dioxide, known as PTZ-DBTO2. Our methodology allows to discern among geometrical and electronic effects induced by the substituent, deeply understanding the relationships existing between charge transfer, spin density, geometrical deformations, and energy modulations between electronic states. By our results, we can finally elucidate, depending on the substituent, the fate of the overall TADF process, quantitatively assessing its efficiency and predicting the color emission. Moreover, the general terms by which this methodology was developed allow its application to any chromophore of interest.
Collapse
Affiliation(s)
- Alejandro Jodra
- Departamento
de Química Analítica, Química Física e
Ingeniería Química, Grupo de Reactividad y Estructura
Molecular (RESMOL), Universidad de Alcalá, Ctra. Madrid-Barcelona, Km 33.600, Alcalá de Henares, Madrid 28871, Spain
| | - Marco Marazzi
- Departamento
de Química Analítica, Química Física e
Ingeniería Química, Grupo de Reactividad y Estructura
Molecular (RESMOL), Universidad de Alcalá, Ctra. Madrid-Barcelona, Km 33.600, Alcalá de Henares, Madrid 28871, Spain
- Instituto
de Investigación Química “Andrés M. del
Río” (IQAR), Universidad de
Alcalá, Ctra.
Madrid-Barcelona, Km 33.600, Alcalá
de Henares, Madrid 28871, Spain
| | - Luis Manuel Frutos
- Departamento
de Química Analítica, Química Física e
Ingeniería Química, Grupo de Reactividad y Estructura
Molecular (RESMOL), Universidad de Alcalá, Ctra. Madrid-Barcelona, Km 33.600, Alcalá de Henares, Madrid 28871, Spain
- Instituto
de Investigación Química “Andrés M. del
Río” (IQAR), Universidad de
Alcalá, Ctra.
Madrid-Barcelona, Km 33.600, Alcalá
de Henares, Madrid 28871, Spain
| | - Cristina García-Iriepa
- Departamento
de Química Analítica, Química Física e
Ingeniería Química, Grupo de Reactividad y Estructura
Molecular (RESMOL), Universidad de Alcalá, Ctra. Madrid-Barcelona, Km 33.600, Alcalá de Henares, Madrid 28871, Spain
- Instituto
de Investigación Química “Andrés M. del
Río” (IQAR), Universidad de
Alcalá, Ctra.
Madrid-Barcelona, Km 33.600, Alcalá
de Henares, Madrid 28871, Spain
| |
Collapse
|
2
|
Fraiponts M, Maes W, Champagne B. Earth Mover's Charge Transfer Distance: A General and Robust Approach for Describing Excited State Locality. J Chem Theory Comput 2024; 20:2751-2760. [PMID: 38407044 DOI: 10.1021/acs.jctc.3c01148] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/27/2024]
Abstract
A novel approach for assessing the extent of electron displacement in optical transitions is proposed by implementing the Earth Mover's Distance (EMD) method, which quantifies the spatial dissimilarity between ground and excited state electron density distributions. In contrast to previous descriptors, this index provides a representative and intuitively understandable distance under a robust and computationally efficient scheme for all possible forms of locality, even in the most difficult to dissect topological cases. The theoretical differences among the existing indices and our method are first illustrated with the help of a simplified model system, followed by a benchmarking of several partial atomic charge models using experimentally relevant push-pull compounds with diverse symmetries. These same molecules are finally employed to further demonstrate the principal advantages of the EMD index and its capabilities in rationalizing charge transfer phenomena.
Collapse
Affiliation(s)
- Mathias Fraiponts
- Laboratory of Theoretical Chemistry (LCT), Theoretical and Structural Physical Chemistry Unit, Namur Institute of Structured Matter, University of Namur, Rue de Bruxelles 61, 5000 Namur, Belgium
- Design & Synthesis of Organic Semiconductors (DSOS), Hasselt University, Agoralaan 1, 3590 Diepenbeek, Belgium
- IMEC, Institute for Materials Research (IMO-IMOMEC), Wetenschapspark 1, 3590 Diepenbeek, Belgium
| | - Wouter Maes
- Design & Synthesis of Organic Semiconductors (DSOS), Hasselt University, Agoralaan 1, 3590 Diepenbeek, Belgium
- IMEC, Institute for Materials Research (IMO-IMOMEC), Wetenschapspark 1, 3590 Diepenbeek, Belgium
| | - Benoît Champagne
- Laboratory of Theoretical Chemistry (LCT), Theoretical and Structural Physical Chemistry Unit, Namur Institute of Structured Matter, University of Namur, Rue de Bruxelles 61, 5000 Namur, Belgium
| |
Collapse
|
3
|
Kim H, Scholes GD, Min SK. Extension of molecules with an inverted singlet-triplet gap with conjugated branches to alter the oscillator strength. Phys Chem Chem Phys 2024; 26:5508-5516. [PMID: 38282516 DOI: 10.1039/d3cp05580a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2024]
Abstract
Molecules that violate Hund's rule and possess negative singlet-triplet gaps (ΔEST) have been actively studied for their potential usage in organic light emitting diodes without the need for thermal activation. However, the weak oscillator strength from the symmetry of such molecules has been recognized as their shortcoming for their application in optoelectronic devices. A group of molecules with a common structural motif involving the original molecule with an inverted gap having branches consisting of conjugated molecules of varied structures and extent of conjugation have been predicted to have desirable oscillator strength, but only few detailed and comprehensive studies regarding the form of excited states and the reason behind the improved oscillator strength have been carried out. We show in this work a series of analyses that suggest that the increase of oscillator strength is correlated with the nature of the excited state changing from a localized excitation to a delocalized excitation involving the central molecule and the branches. The resulting oscillator strength thus depends on the energetic matching of the branching molecule and the central molecule, rather than solely the oscillator strength of the central molecule. From the ΔEST inversion point of view, the static correlation with low-lying doubly excited configurations, the key mechanism behind the inversion in the localized excited state, weakens as the excited states delocalize. As a consequence, the dynamic correlation has a more decisive effect in determining the singlet-triplet gap.
Collapse
Affiliation(s)
- Hwon Kim
- Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST), South Korea.
| | - Gregory D Scholes
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA
| | - Seung Kyu Min
- Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST), South Korea.
| |
Collapse
|
4
|
de Sousa LE, de Silva P. Photophysics of Solvated Molecules: Computational Protocol Combining Nuclear Ensemble and Nonequilibrium State-Specific Solvation Methods. J Phys Chem A 2023; 127:8200-8208. [PMID: 37728994 DOI: 10.1021/acs.jpca.3c03533] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/22/2023]
Abstract
Efficient calculations of the photophysical properties of molecules are essential for both understanding experimental results and accelerating materials discovery through computational simulations. However, to achieve accurate results, the effects of the surrounding medium must be taken into account. Here, we present a computational protocol that combines the nuclear ensemble method with a nonequilibrium state-specific polarizable continuum model to simulate absorption, fluorescence, phosphorescence, and intersystem crossing processes. Additionally, we introduced an extrapolation strategy that enables predictions for multiple solvents without incurring additional computational costs. We demonstrate the method's effectiveness by modeling the photophysical properties of a molecule that exhibits thermally activated delayed fluorescence, showcasing how these properties vary with solvent polarity. We also provide insight into the relationship between the solvent and photophysics by using ensemble analysis to rationalize simulation results. Furthermore, we introduce a metric for the intensity of the charge transfer character of electronic states and demonstrate how vibrations can significantly mix the electronic character of excited states. Overall, this work presents a computational approach that offers new insights into the photophysics of molecules and has the potential to advance materials discovery.
Collapse
Affiliation(s)
- Leonardo Evaristo de Sousa
- Department of Energy Conversion and Storage, Technical University of Denmark, Anker Engelunds Vej 301, 2800 Kongens Lyngby, Denmark
| | - Piotr de Silva
- Department of Energy Conversion and Storage, Technical University of Denmark, Anker Engelunds Vej 301, 2800 Kongens Lyngby, Denmark
| |
Collapse
|
5
|
Hall D, Sancho-García JC, Pershin A, Beljonne D, Zysman-Colman E, Olivier Y. Benchmarking DFT Functionals for Excited-State Calculations of Donor-Acceptor TADF Emitters: Insights on the Key Parameters Determining Reverse Inter-System Crossing. J Phys Chem A 2023. [PMID: 37196185 DOI: 10.1021/acs.jpca.2c08201] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
The importance of intermediate triplet states and the nature of excited states has gained interest in recent years for the thermally activated delayed fluorescence (TADF) mechanism. It is widely accepted that simple conversion between charge transfer (CT) triplet and singlet excited states is too crude, and a more complex route involving higher-lying locally excited triplet excited states has to be invoked to witness the magnitude of the rate of reverse inter-system crossing (RISC) rates. The increased complexity has challenged the reliability of computational methods to accurately predict the relative energy between excited states as well as their nature. Here, we compare the results of widely used density functional theory (DFT) functionals, CAM-B3LYP, LC-ωPBE, LC-ω*PBE, LC-ω*HPBE, B3LYP, PBE0, and M06-2X, against a wavefunction-based reference method, Spin-Component Scaling second-order approximate Coupled Cluster (SCS-CC2), in 14 known TADF emitters possessing a diversity of chemical structures. Overall, the use of the Tamm-Dancoff Approximation (TDA) together with CAM-B3LYP, M06-2X, and the two ω-tuned range-separated functionals LC-ω*PBE and LC-ω*HPBE demonstrated the best agreement with SCS-CC2 calculations in predicting the absolute energy of the singlet S1, and triplet T1 and T2 excited states and their energy differences. However, consistently across the series and irrespective of the functional or the use of TDA, the nature of T1 and T2 is not as accurately captured as compared to S1. We also investigated the impact of the optimization of S1 and T1 excited states on ΔEST and the nature of these states for three different functionals (PBE0, CAM-B3LYP, and M06-2X). We observed large changes in ΔEST using CAM-B3LYP and PBE0 functionals associated with a large stabilization of T1 with CAM-B3LYP and a large stabilization of S1 with PBE0, while ΔEST is much less affected considering the M06-2X functional. The nature of the S1 state barely evolves after geometry optimization essentially because this state is CT by nature for the three functionals tested. However, the prediction of the T1 nature is more problematic since these functionals for some compounds interpret the nature of T1 very differently. SCS-CC2 calculations on top of the TDA-DFT optimized geometries lead to a large variation in terms of ΔEST and the excited-state nature depending on the chosen functionals, further stressing the large dependence of the excited-state features on the excited-state geometries. The presented work highlights that despite good agreement of energies, the description of the exact nature of the triplet states should be undertaken with caution.
Collapse
Affiliation(s)
- David Hall
- Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St Andrews, KY16 9ST St Andrews, U.K
- Laboratory for Chemistry of Novel Materials, University of Mons, 7000 Mons, Belgium
| | | | - Anton Pershin
- Wigner Research Centre for Physics, P.O. Box 49, 1121 Budapest, Hungary
| | - David Beljonne
- Laboratory for Chemistry of Novel Materials, University of Mons, 7000 Mons, Belgium
| | - Eli Zysman-Colman
- Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St Andrews, KY16 9ST St Andrews, U.K
| | - Yoann Olivier
- Laboratory for Computational Modeling of Functional Materials, Namur Institute of Structured Matter, University of Namur, Rue de Bruxelles, 61, 5000 Namur, Belgium
| |
Collapse
|