Spectroscopic Quantification of the Inverted Singlet–Triplet Gap in Pentaazaphenalene

Journal of the American Chemical Society, Journal Year: 2024, Volume and Issue: 146(23), P. 15688 - 15692

Published: May 30, 2024

We report the direct and accurate spectroscopic quantification of inverted singlet–triplet gap in 1,3,4,6,9b-pentaazaphenalene. This measurement is achieved by directly probing lowest singlet triplet states via high-resolution cryogenic anion photoelectron spectroscopy. The assignment first excited state confirmed visible absorption spectroscopy an argon matrix at 20 K. Our measurements yield with ΔEST= −0.047(7) eV. presented here allows for evaluation various computational electronic structure methods highlights critical importance proper description double excitation character these states. Overall, this study validates idea that despite Hund's multiplicity rule, useful organic chromophores can have inherently gaps.

Language: Английский

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Molecular Geometry Impact on Deep Learning Predictions of Inverted Singlet–Triplet Gaps

The Journal of Physical Chemistry A, Journal Year: 2024, Volume and Issue: 128(12), P. 2417 - 2426

Published: March 14, 2024

We present a deep learning model able to predict excited singlet–triplet gaps with mean absolute error (MAE) of ≈20 meV obtain potential inverted (IST) candidates. exploit cutting-edge spherical message passing graph neural networks designed specifically for generating 3D representations in molecular learning. In nutshell, the takes as input list unsaturated heavy atom Cartesian coordinates and atomic numbers, producing output. exploited available large data collections train on ≈40,000 heterogeneous density functional theory (DFT) geometries ADC(2)/cc-pVDZ gaps. ascertain predictive power from quantitative perspective obtaining predictions test set ≈14,000 molecules, whose have been generated at DFT level (the same employed training set), GFN2-xTB level, through Molecular Mechanics. notice performance degradation upon switching lower-quality geometries, ones maintaining satisfactory results (MAE ≈ 50 MAE 180 generalized AMBER force field geometries), hinting caution when dealing specific chemical classes. Finally, we verify qualitative point view, different ≈15,000 molecules already used identify new IST molecules. obtained using both experimental X-ray candidates similar those provided by quantum methods, clear hints path toward improved performance.

Language: Английский

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Development of an Organic Emitter Exhibiting Reverse Intersystem Crossing Faster than Intersystem Crossing

Angewandte Chemie International Edition, Journal Year: 2024, Volume and Issue: 63(35)

Published: Aug. 13, 2024

Abstract In thermally activated delayed fluorescence (TADF)‐based organic light‐emitting diodes (OLEDs), acceleration of reverse intersystem crossing (RISC) and suppression (ISC) are demanded to shorten a lifetime triplet excitons. As system realizing RISC faster than ISC, inverted singlet‐triplet excited states (iST) with negative energy difference (Δ E ST ) between the lowest singlet have been gathering much attention recently. Here, we focused on an asymmetric hexa‐azaphenalene (A6AP) core obtain new insight into iST. Based A6AP, newly designed A6AP‐Cz calculated Δ −44 meV. The experimental studies synthesized revealed that ( τ DF was only 54 ns, which shortest among all materials. rate constant k =1.9×10 7 s −1 greater ISC =1.0×10 ). experimentally confirmed from 1) (−45 meV) 2) temperature‐dependent . 3) onsets phosphorescence spectra at 77 K also supported evidence (−73 meV). This study demonstrated potential A6AP as iST for first time.

Language: Английский

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Resilience of Hund's rule in the chemical space of small organic molecules

Physical Chemistry Chemical Physics, Journal Year: 2024, Volume and Issue: 26(20), P. 14505 - 14513

Published: Jan. 1, 2024

High-throughput ab initio calculations and data-mining reveal Hund's rule to prevail across the chemical space of small organic molecules with systematically varying compositions structures.

Language: Английский

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ΔDFT Predicts Inverted Singlet–Triplet Gaps with Chemical Accuracy at a Fraction of the Cost of Wave Function-Based Approaches

The Journal of Physical Chemistry Letters, Journal Year: 2024, Volume and Issue: 15(31), P. 8065 - 8077

Published: July 31, 2024

Efficient OLEDs need to quickly convert singlet and triplet excitons into photons. Molecules with an inverted singlet–triplet energy gap (INVEST) are promising candidates for this task. However, typical INVEST molecules have drawbacks like too low oscillator strengths excitation energies. High-throughput screening could identify suitable molecules, but existing methods problematic: The workhorse method TD-DFT cannot reproduce inversion, while wave function-based slow. This study proposes a state-specific based on unrestricted Kohn–Sham DFT common hybrid functionals. Tuned the new INVEST15 benchmark set, achieves error of less than 1 kcal/mol, which is traced back cancellation between spin contamination dynamic correlation. Applied larger structurally diverse NAH159 set in black-box fashion, maintains small (1.2 kcal/mol) accurately predicts signs 83% cases, confirming its robustness suitability workflows.

Language: Английский

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Computational Design of Boron-Free Triangular Molecules with Inverted Singlet-Triplet Energy Gap

Physical Chemistry Chemical Physics, Journal Year: 2024, Volume and Issue: 26(28), P. 19130 - 19137

Published: Jan. 1, 2024

A novel, computationally designed, class of triangular-shape organic molecules with an inverted singlet-triplet (IST) energy gap is investigated

Language: Английский

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Rational Design of Organic Emitters with Inverted Singlet–Triplet Gaps for Enhanced Exciton Management

The Journal of Physical Chemistry A, Journal Year: 2024, Volume and Issue: 128(34), P. 7114 - 7123

Published: Aug. 19, 2024

In organic light-emitting diodes (OLEDs), the pursuit of efficient molecular emitters has led to development thermally activated delayed fluorescence (TADF) molecules. While TADF compounds have promising properties, they face challenges such as energy gap constraints and uphill exciton transfer. Inverted (INVEST) offer a novel solution with an inverted singlet–triplet (ΔEST) gap, enabling utilization excitons. This study examines design computational analysis array molecules, including 23 INVEST remaining positive gaps. Within STEOM-DLPNO–CCSD framework, we explore role various fragments in determining ΔEST. We also assess importance dynamic spin-polarization (DSP) obtained via Pariser–Parr–Pople (PPP) scheme determination. Exciting trends emerged from our results, pentalene-containing consistently manifesting negative ΔEST values while their naphthalene counterparts exhibited contrasting behavior. Moreover, observed DSP correlates Overall, this research advances OLED materials through analysis, offering avenues for optimizing management enhancing device performance.

Language: Английский

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The Role of Theoretical Calculations for INVEST Systems: Complementarity Between Theory and Experiments and Rationalization of the Results

Advanced Optical Materials, Journal Year: 2025, Volume and Issue: unknown

Published: March 5, 2025

Abstract Here, the key role played by theoretical calculations for molecules presenting an inverted singlet‐triplet excited state (e.g. S 1 and T ) energy difference, or Δ E ST < 0, whose interest has steadily raised in recent years fostered experimental advances showing negative values a collection of real‐world systems is reviewed. The evolution computational efforts from pioneering on reduced set prototypical covered, to high‐throughput virtual screenings thousands identify new molecular scaffolds tune properties other than excitation energies, describe necessary benchmarking methods done parallel along years. Overall, complementarity prompted discovery more displaying 0 values, basic design principles are rationalized thus reviewed here too, while allowing at same time find which offer reasonable trade‐off between accuracy cost.

Language: Английский

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Impact of Structure on Excitation Energies and S₁‐T₁ Energy Gaps of Asymmetrical Systems of Interest for Inverted Singlet‐Triplet Gaps

Journal of Computational Chemistry, Journal Year: 2025, Volume and Issue: 46(8)

Published: March 26, 2025

Computational investigations of Inverted Singlet-Triplet (INVEST) emitters often rely on ADC(2) and TD-DFT excitation energies (EEs) obtained with the vertical approximation. Here, we first considered several cyclazine derivatives examine sensitivity EEs (VEEs) as well singlet-triplet gaps, ΔES1T1 to level at which ground state (S0) structure was optimized. For cyclazine, VEEs gaps from or are spread over a narrow range (< 0.064 eV) whether S0 is optimized various DFT, CCSD, RI-MP2 methods. However, for asymmetric cyclazines, depending protocol optimizing structures, not only substantially wider (up 0.75 but so 0.30 eV), leading cases where, different one obtains positive significantly negative gaps. We relate this behavior introduction significant asymmetry bond-length variations in derivatives, formed by ligand functionalization modification core. On more note, adiabatic (AEEs) display lower (7-30× less) geometry optimization protocols than their analogs. Crucially, M06-HF functional 100% non-local exchange provides closest available CCSD(T) data. show that effect exists also other frameworks (e.g., azulene, pentaazaphenalene, non-alternant polycyclic hydrocarbons) have been INVEST property, broader up 1.19 eV 0.62 eV. emitters, it therefore extremely important judiciously choose computational geometries, computing

Language: Английский

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Computational Design of Molecules Having Less Overlapping HOMO and LUMO in the Same Plane

The Journal of Physical Chemistry A, Journal Year: 2025, Volume and Issue: unknown

Published: April 3, 2025

The negative energy difference between singlet and triplet excited states (ΔEST) is currently attracting significant attention; however, molecular designs remain largely confined to azaphenalene structures, as reported by Leupin Wirz in 1980. To show ΔEST, a maximally separated highest occupied orbital (HOMO) lowest unoccupied (LUMO) arrangement crucial minimizing the exchange interaction state. We revisited electronic structure of cyclazine, consisting cyclododecahexaene ([12]annulene) central nitrogen atom. 12 π-electrons peripheral cyclic oligoene play an important role achieving less overlapping HOMO LUMO arrangement, bridging atom inside produces while maintaining stable planar structure. Based on these insights, we designed set 10 molecules which number (N) 16, 20, 24, satisfying N = 4·n (n 4, 5, 6), further 11 extended 14, 18, 22, 26, + 2 3, 6). HOMO, LUMO, (K), ΔEST were calculated using configuration singles, TD-DFT, equation motion coupled-cluster singles doubles (EOM-CCSD), with optimized without any symmetry constraint. Among structures 4·n, only bond alternation exhibit small K ΔEST. In contrast, among 2, none arrangement. both no EOM-CCSD calculation. findings this study will pave way for broader exhibiting where overlap essential.

Language: Английский

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