Ultrafast Computational Screening of Molecules with Inverted Singlet–Triplet Energy Gaps Using the Pariser–Parr–Pople Semiempirical Quantum Chemistry Method

Jorner, Kjell; Pollice, Robert; Lavigne, Cyrille; Aspuru-Guzik, Alán

doi:10.1021/acs.jpca.3c06357

Cited by 9 publications

(4 citation statements)

References 72 publications

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“…Selected examples include systems 14 and 15, where TDA-DFT underestimates the emission energies by over 0.5 eV, or 20, 21, and 22, which reverse their relative order, and all of which are accurately described by the ΔDFT-based methods. While seemingly acceptable in a benchmark considering mostly statistical performance, it should be noted that such severe deviations for several of the studied molecules can critically deteriorate the performance of screening and optimization tasks in material design. , In this respect, having no outliers >0.3 eV is more important than eliminating small statistical deviations of ∼0.1 eV.…”

Section: Resultsmentioning

confidence: 99%

Benchmarking Charge-Transfer Excited States in TADF Emitters: ΔDFT Outperforms TD-DFT for Emission Energies

Froitzheim,

Kunze,

Grimme

et al. 2024

J. Phys. Chem. A

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Charge-transfer (CT) excited states are crucial to organic light-emitting diodes (OLEDs), particularly to those based on thermally activated delayed fluorescence (TADF). However, accurately modeling CT states remains challenging, even with modern implementations of (time-dependent) density functional theory [(TD-)DFT], especially in a dielectric environment. To identify shortcomings and improve the methodology, we previously established the STGABS27 benchmark set with highly accurate experimental references for the adiabatic energy gap between the lowest singlet and triplet excited states (ΔE ST ). Here, we diversify this set to the STGABS27-EMS benchmark by including experimental emission energies (E em ) and use this new set to (re)evaluate various DFT-based approaches. Surprisingly, these tests demonstrate that a state-specific (un)restricted open-shell Kohn−Sham (U/ROKS) DFT coupled with a polarizable continuum model for perturbative state-specific nonequilibrium solvation (ptSS-PCM) provides exceptional accuracy for predicting E em over a wide range of density functionals. In contrast, the main workhorse of the field, Tamm−Dancoff-approximated TD-DFT (TDA-DFT) paired with the same ptSS-PCM, is distinctly less accurate and strongly functional-dependent. More importantly, while TDA-DFT requires the choice of two very different density functionals for good performance on either ΔE ST or E em , the time-independent U/ROKS/PCM approaches deliver excellent accuracy for both quantities with a wide variety of functionals.

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Section: Resultsmentioning

confidence: 99%

Benchmarking Charge-Transfer Excited States in TADF Emitters: ΔDFT Outperforms TD-DFT for Emission Energies

Froitzheim,

Kunze,

Grimme

et al. 2024

J. Phys. Chem. A

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“…Various propositions have been made for the conditions or structural motifs required to achieve a negative ΔE ST through the minimization of the exchange contributions, like doping to achieve high symmetry point groups or double-bond delocalization. , However, inverted singlet–triplet gap predictions require correlated methodologies that include at least double excitations while some studies point to the need for the inclusion of triple-excitation with large basis sets, − to properly describe the stabilization of the S 1 state via dynamic spin polarization in these materials . Indeed, single-excitation computational methods typically used in computational excited-state studies were unable to predict inverted singlet–triplet gaps. , We also note the recent success in using semiempirical methods to reproduce inverted singlet–triplet gaps. ,, The difficulty in modeling these systems computationally is exacerbated by the dearth of experimental literature on the photophysical properties of these systems.…”

Section: Introductionmentioning

confidence: 99%

Computational Investigations of the Detailed Mechanism of Reverse Intersystem Crossing in Inverted Singlet–Triplet Gap Molecules

Valverde,

Ser,

Ricci

et al. 2024

ACS Appl. Mater. Interfaces

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Inverted singlet–triplet gap (INVEST) materials have promising photophysical properties for optoelectronic applications due to an inversion of their lowest singlet (S1) and triplet (T1) excited states. This results in an exothermic reverse intersystem crossing (rISC) process that potentially enhances triplet harvesting, compared to thermally activated delayed fluorescence (TADF) emitters with endothermic rISCs. However, the processes and phenomena that facilitate conversion between excited states for INVEST materials are underexplored. We investigate the complex potential energy surfaces (PESs) of the excited states of three heavily studied azaphenalene INVEST compounds, namely, cyclazine, pentazine, and heptazine using two state-of-the-art computational methodologies, namely, RMS-CASPT2 and SCS-ADC(2) methods. Our findings suggest that ISC and rISC processes take place directly between the S1 and T1 electronic states in all three compounds through a minimum-energy crossing point (MECP) with an activation energy barrier between 0.11 to 0.58 eV above the S1 state for ISC and between 0.06 and 0.36 eV above the T1 state for rISC. We predict that higher-lying triplet states are not populated, since the crossing point structures to these states are not energetically accessible. Furthermore, the conical intersection (CI) between the ground and S1 states is high in energy for all compounds (between 0.4 to 2.0 eV) which makes nonradiative decay back to the ground state a relatively slow process. We demonstrate that the spin-orbit coupling (SOC) driving the S1-T1 conversion is enhanced by vibronic coupling with higher-lying singlet and triplet states possessing vibrational modes of proper symmetry. We also rationalize that the experimentally observed anti-Kasha emission of cyclazine is due to the energetically inaccessible CI between the bright S2 and the dark S1 states, hindering internal conversion. Finally, we show that SCS-ADC(2) is able to qualitatively reproduce excited state features, but consistently overpredict relative energies of excited state structural minima compared to RMS-CASPT2. The identification of these excited state features elaborates design rules for new INVEST emitters with improved emission quantum yields.

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“…In recent studies, also non-phenalene-based organic molecules were investigated, specifically focusing on non-alternant cyclic hydrocarbons. 25–30…”

Section: Introductionmentioning

confidence: 99%

Computational design of boron-free triangular molecules with inverted singlet–triplet energy gap

Duszka,

Rode,

Sobolewski

2024

Phys. Chem. Chem. Phys.

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Ultrafast Computational Screening of Molecules with Inverted Singlet–Triplet Energy Gaps Using the Pariser–Parr–Pople Semiempirical Quantum Chemistry Method

Cited by 9 publications

References 72 publications

Benchmarking Charge-Transfer Excited States in TADF Emitters: ΔDFT Outperforms TD-DFT for Emission Energies

Benchmarking Charge-Transfer Excited States in TADF Emitters: ΔDFT Outperforms TD-DFT for Emission Energies

Computational Investigations of the Detailed Mechanism of Reverse Intersystem Crossing in Inverted Singlet–Triplet Gap Molecules

Computational design of boron-free triangular molecules with inverted singlet–triplet energy gap

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