Rapid predictions of the colour purity of luminescent organic molecules

Penfold, Thomas J.; Ahmad, Sajjad; Eng, Julien

doi:10.1039/d1tc04748e

Cited by 21 publications

(26 citation statements)

References 73 publications

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“…We note that on moving from O to S and to Se in a particular series, the corresponding geometries gradually become more puckered (see Figure 3), since the van der Waals radius of the chalcogen atoms increases. Such structural strains are known to increase the emission FWHM, as reported by Ahmad et al; 67 however, the molecules shown in Figure 2 are designed by fusing together adjacent phenyl rings, so that their cores are expected to remain rigid. We recall that rigid structures help minimize non-radiative losses associated with skeleton and vibrational motions, which is beneficial to the achievement of narrowband emission and high luminescence quantum yields.…”

Section: Resultsmentioning

confidence: 83%

Enhancement of Thermally Activated Delayed Fluorescence (TADF) in Multi-Resonant Emitters via Control of Chalcogen Atom Embedding

2022

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Multi-resonant thermally activated delayed fluorescence (MR-TADF) emitters based on heteroatom-embedded organoboron molecules are emerging as interesting candidates for organic light-emitting diode (OLED) applications. This is mainly due to their high photoluminescence quantum yields, thermal and chemical stabilities, and color purity. However, their reverse intersystem crossing (RISC) rates generally remain relatively small. To circumvent that drawback, here, we expand on our recent investigations and design a series of MR-TADF molecules through the incorporation of chalcogen atoms (O, S, or Se) in a nitrogen-centered organoboron emitter consisting of an ADBNA (13b-aza-5,9-diboranaphtho[3,2,1-de]anthracene) core. The results obtained by means of highly correlated wave function-based calculations indicate that these molecules (i) retain small singlet−triplet energy gaps (0.1−0.2 eV) and (ii) have a highly emissive nature (radiative rates around 10 8 s −1 ) due to the alternating distribution of electron-rich and electron-poor regions related to multi-resonant effects. Importantly, the RISC rates, especially for emitters containing selenium atoms, can be as high as 10 8 s −1 , which comes from both increased spin−orbit couplings and contributions from the second excited triplet (T 2 ) states. Coupled with the increased core rigidity associated with a larger number of chalcogen atoms that bridge and fuse rings together, these characteristics make these MR-TADF molecules promising strong emitters with high color purity. Our calculations further underline that it is not only the nature of the chalcogen atoms (O, S, or Se) but also their positions within the backbone that have a critical impact on the emission color, which can vary from deep blue to yellow-green.

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Section: Resultsmentioning

confidence: 83%

Enhancement of Thermally Activated Delayed Fluorescence (TADF) in Multi-Resonant Emitters via Control of Chalcogen Atom Embedding

2022

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“…As described above, TBPe (Fig. 1a) is a narrowband fluorescent emitter 44 and given the rigidity required in the molecular structure to achieve narrow emission spectra 66 one would expect the LVC model to provide an accurate description of TBPe excited states. In this section we focus on the lowest excited triplet (T 1 ) and singlet (S 1 ) states which both exhibit π → π* excitation localised on the central aromatic moiety of TBPe .…”

Section: Resultsmentioning

confidence: 99%

Mind the GAP: quantifying the breakdown of the linear vibronic coupling Hamiltonian

Eng

Penfold

2023

Phys. Chem. Chem. Phys.

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“…While a large ΔE FC gap would provide sufficient vibrational excess energy to overcome the

{{\rm{\Delta E}}^{{\rm{Sym}}} }

, this effect would only be present at short time delays (∼10 ps) due to vibrational cooling [53] . However, it is noted that a large ΔE FC may also prove detrimental to achieving narrow emission width [54] …”

Section: Resultsmentioning

confidence: 99%

Tailoring Donor‐Acceptor Emitters to Minimise Localisation Induced Quenching of Thermally Activated Delayed Fluorescence

Penfold

Eng

2022

ChemPhotoChem

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By inverting the common structural motif of thermally activated delayed fluorescence (TADF) materials to a rigid donor core and multiple peripheral acceptors, it has been shown possible to achieve both a reverse intersystem crossing (rISC) rate > 1 × 10 7 s À 1 and a unity photoluminescence quantum yield [Dos Santos et al. Adv. Sci. 5 (2018) 1700989]. However, the rISC rate in this motif is quenched by localisation of the excited state electronic structure which causes in-equivalence between the peripheral acceptors. In this paper, we explore a series of related molecular targets which seek to reduce the effect of localisation on the rISC rates. This includes structures that contain donors exhibiting three-fold or four-fold symmetry and different degrees of steric hindrance around the donor-acceptor bond with the objective of using steric hindrance to exert finer conformational control of the excited state dynamics to enhance functional properties. We demonstrate that a triazatruxene central donor is most effective for TADF owing to the energetic position of the locally excited state, while cyanobenzonitriles are the most effective acceptors for reducing the effect of localisation on the electronic structure. These also push the emission into the blue region of the spectrum, opening the possibilities for this to be a pathway to develop efficient blue TADF emitters.

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Rapid predictions of the colour purity of luminescent organic molecules

Abstract: Designing luminescent organic materials exhibiting narrowband emission is crucial for achieving high resolution and energy efficient organic light emitting diodes (OLEDs), but remains a significant challenge. Herein we establish the...

Cited by 21 publications

References 73 publications

Enhancement of Thermally Activated Delayed Fluorescence (TADF) in Multi-Resonant Emitters via Control of Chalcogen Atom Embedding

Enhancement of Thermally Activated Delayed Fluorescence (TADF) in Multi-Resonant Emitters via Control of Chalcogen Atom Embedding

Mind the GAP: quantifying the breakdown of the linear vibronic coupling Hamiltonian

Tailoring Donor‐Acceptor Emitters to Minimise Localisation Induced Quenching of Thermally Activated Delayed Fluorescence

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