Photoexcited triplet states of twisted acenes investigated by Electron Paramagnetic Resonance

Tait, Claudia E.; Bedi, Anjan; Gidron, Ori; Behrends, Jan

doi:10.1039/c9cp04135d

Cited by 12 publications

(19 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…While optical spectroscopy has proved a powerful tool to examine the photophysics and spinconversion rates in TADF 30,31,35,36 , trESR provides a complementary window into the underlying spin physics. TrESR is sensitive to paramagnetic states and can therefore probe the formation dynamics and coupling mechanisms of triplet excitons 37 , as highlighted by broad applications in studying triplet excitons in organic photovoltaics [38][39][40] , singlet fission [41][42][43][44] , photosensitizers 37,[45][46][47] , and molecular electronics 48,49 . Because trESR is not sensitive to singlet excitons (due to their diamagnetism) it can only explicitly probe forward ISC.…”

mentioning

confidence: 99%

Electron spin resonance resolves intermediate triplet states in delayed fluorescence

et al. 2021

View full text Add to dashboard Cite

Molecular organic fluorophores are currently used in organic light-emitting diodes, though non-emissive triplet excitons generated in devices incorporating conventional fluorophores limit the efficiency. This limit can be overcome in materials that have intramolecular charge-transfer excitonic states and associated small singlet-triplet energy separations; triplets can then be converted to emissive singlet excitons resulting in efficient delayed fluorescence. However, the mechanistic details of the spin interconversion have not yet been fully resolved. We report transient electron spin resonance studies that allow direct probing of the spin conversion in a series of delayed fluorescence fluorophores with varying energy gaps between local excitation and charge-transfer triplet states. The observation of distinct triplet signals, unusual in transient electron spin resonance, suggests that multiple triplet states mediate the photophysics for efficient light emission in delayed fluorescence emitters. We reveal that as the energy separation between local excitation and charge-transfer triplet states decreases, spin interconversion changes from a direct, singlet-triplet mechanism to an indirect mechanism involving intermediate states.

show abstract

mentioning

confidence: 99%

Electron spin resonance resolves intermediate triplet states in delayed fluorescence

et al. 2021

View full text Add to dashboard Cite

show abstract

“… 9 , 10 , 18 , 20 We have previously demonstrated that as twisting increases, the rate of ISC to the triplet state also increases. 21 Therefore, it is expected that as the twisting increases, the mechanism that involves ISC will become more dominant. When using MB as the sensitizer, the faster reaction rate with twisting can be explained by the calculated lower energy for the transition state of twisted Ant-C3 compared with less-twisted Ant-C6 , as detailed later.…”

mentioning

confidence: 99%

Effect of Twisting on the Capture and Release of Singlet Oxygen by Tethered Twisted Acenes

2020

Self Cite

View full text Add to dashboard Cite

The use of polyaromatic hydrocarbons to capture and release singlet oxygen is of considerable importance in materials chemistry, synthesis, and photodynamic therapy. Here we studied the ability of a series of tethered twistacenes, possessing different degrees of backbone twist, to capture and release singlet oxygen via the reversible Diels–Alder reaction. When the twistacene acts as both a sensitizer and a diene, the photo-oxidation rate depends on the extinction coefficient of the irradiation wavelength. However, when the twistacenes function solely as a diene, the rate of photo-oxidation increases with increasing twist. The rate of the reverse reaction, the singlet oxygen release, also increases with increasing twist. The calculated transition state energy decreases with increasing twist, which can explain the observed trend. The presence of the tether significantly increases the reversibility of the reaction, which can proceed in repeated forward and reverse cycles in very high yield under mild conditions, as required for molecular switches.

show abstract

“…[1e,10] In the twistacene case, the reduction in fluorescence quantum efficiency arose from stabilization of the triplet state with increasing twist. [11] The synthetic challenges for obtaining curved PAHs are exemplified in the field of carbon nanobelts (CNBs). Cyclacene [9a,20] and the "Vögtle belt" [12] are examples of desired molecules that have not yet been synthesized.…”

Section: Introductionmentioning

confidence: 99%

“…[ 1e , 10 ] In the twistacene case, the reduction in fluorescence quantum efficiency arose from stabilization of the triplet state with increasing twist. [11] …”

Section: Introductionmentioning

confidence: 99%

Bending versus Twisting Acenes – A Computational Study

et al. 2021

Self Cite

View full text Add to dashboard Cite

In memory of François DiederichPolycyclic aromatic hydrocarbons (PAHs) are widely used in organic electronic devices. The electronic, magnetic, and optical properties of PAHs can be tuned by structural modifications to the aromatic backbone to introduce an inherent distortion from planarity, such as bending or twisting. However, it remains difficult to isolate and control the effects of such distortions. Here, we sought to understand how backbone twisting and bending affect the electronic properties of acenes, as models for larger PAHs. We found that, even when highly distorted from planarity (30°per ring), acenes maintain their aromatic character and π orbital delocalization with minor mixing of the σ and π orbitals. In addition, the energy gap between the HOMO and LUMO decreases with increasing twist, while the gap is hardly affected by bending, since the energy of both orbitals increase to a similar extent. For bent acenes in the triplet state, the spin becomes more localized with increasing bend, whereas twisting produces an evenly distributed spin delocalization. These findings can guide the synthesis of PAHs with tailored properties.

show abstract

Photoexcited triplet states of twisted acenes investigated by Electron Paramagnetic Resonance

Abstract: Increased twisting of the anthracene core affects the ISC efficiency and induces changes in zero-field splitting parameters, spin polarisation and hyperfine couplings.

Cited by 12 publications

References 33 publications

Electron spin resonance resolves intermediate triplet states in delayed fluorescence

Electron spin resonance resolves intermediate triplet states in delayed fluorescence

Effect of Twisting on the Capture and Release of Singlet Oxygen by Tethered Twisted Acenes

Bending versus Twisting Acenes – A Computational Study

Contact Info

Product

Resources

About