The lowest triplet state of toluene by microwave induced delayed phosphorescence

Vergragt, Ph.J.; Waals, J.H. van der

doi:10.1016/0009-2614(74)89037-8

Cited by 23 publications

(4 citation statements)

References 21 publications

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“…The pinnacle carbon atoms are expected to be the ones carrying the methyl-substituents due to the stabilizing effect of methyl-groups on the un-paired electron of the quasi-radicaloid prefulvene-like structure 48 . This reasoning is fully consistent with the observation that the lowest triplet states of toluene and p-xylene exhibit quinoidal structures (Figure 2) with the methyl-groups positioned to support the diradicaloid species as found by EPR measurements 49,50 and quantum chemical calculations 48 . Quinoidal triplet structures of benzene derivatives have further been observed by time-resolved electron diffraction experiments by Zewail and coworkers 51 .…”

Section: Introductionsupporting

confidence: 83%

Distortion dependent intersystem crossing: A femtosecond time-resolved photoelectron spectroscopy study of benzene, toluene, and p-xylene

Stephansen¹,

Sølling²

2017

Structural Dynamics

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The competition between ultrafast intersystem crossing and internal conversion in benzene, toluene, and p-xylene is investigated with time-resolved photoelectron spectroscopy and quantum chemical calculations. By exciting to S2 out-of-plane symmetry breaking, distortions are activated at early times whereupon spin-forbidden intersystem crossing becomes (partly) allowed. Natural bond orbital analysis suggests that the pinnacle carbon atoms distorting from the aromatic plane change hybridization between the planar Franck-Condon geometry and the deformed (boat-shaped) S2 equilibrium geometry. The effect is observed to increase in the presence of methyl-groups on the pinnacle carbon-atoms, where largest extents of σ and π orbital-mixing are observed. This is fully consistent with the time-resolved spectroscopy data: Toluene and p-xylene show evidence for ultrafast triplet formation competing with internal conversion, while benzene appears to only decay via internal conversion within the singlet manifold. For toluene and p-xylene, internal conversion to S1 and intersystem crossing to T3 occur within the time-resolution of our instrument. The receiver triplet state (T3) is found to undergo internal conversion in the triplet manifold within ≈100–150 fs (toluene) or ≈180–200 fs (p-xylene) as demonstrated by matching rise and decay components of upper and lower triplet states. Overall, the effect of methylation is found to both increase the intersystem crossing probability and direct the molecular axis of the excited state dynamics.

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Section: Introductionsupporting

confidence: 83%

Distortion dependent intersystem crossing: A femtosecond time-resolved photoelectron spectroscopy study of benzene, toluene, and p-xylene

Stephansen¹,

Sølling²

2017

Structural Dynamics

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“…As a result, it should be noted that the order of the T 1 sublevels was determined to be T x > T y > T z in energy for MBC. The D values of toluene and formaldehyde were estimated to be 0.146 and 0.42 cm –1 , respectively. , The D value of ethylene has been calculated: | D | = 0.1847 cm –1 . If the two unpaired electrons localized on the tolyl fragment, the ethylene one, or the carbonyl one, the | D | value of MBC should be larger than 0.0901 cm –1 .…”

Section: Resultsmentioning

confidence: 99%

Optical and Time-Resolved Electron Paramagnetic Resonance Studies of the Excited States of a UV-B Absorber (4-Methylbenzylidene)camphor

et al. 2013

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The excited states of UV-B absorber (4-methylbenzylidene)camphor (MBC) have been studied through measurements of UV absorption, phosphorescence, triplet-triplet (T-T) absorption, and steady-state and time-resolved electron paramagnetic resonance spectra in ethanol. The energy level and lifetime of the lowest excited triplet (T(1)) state of MBC were determined. The energy level of the T(1) state of MBC is much lower than that of photolabile 4-tert-butyl-4'-methoxydibenzoylmethane. The weak phosphorescence and strong time-resolved EPR signals, and T-T absorption band of MBC were observed. These facts suggest that the significant proportion of the lowest excited singlet (S(1)) molecules undergoes intersystem crossing to the T(1) state and the deactivation process from the T(1) state is predominantly radiationless. The quantum yields of singlet oxygen production by MBC determined by time-resolved near-IR luminescence measurements are 0.05 ± 0.01 and 0.06 ± 0.01 in ethanol and in acetonitrile, respectively. The photostability of MBC arises from the (3)ππ* character in the T(1) state. The zero-field splitting parameters in the T(1) state are D = 0.0901 cm(-1) and E = -0.0498 cm(-1). The sublevel preferentially populated by intersystem crossing is T(y) (y close to in-plane short axis and to the C═O direction).

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“…The D* values of the T 1 states of 4-methylanisole, 4-fluoroanisole, toluene, ethylene and formaldehyde were estimated to be 0.1547, 0.1560, 0.1517, 0.4310 and 0.43 cm À1 , respectively (42)(43)(44)(45)(46). As the observed D** value of EHMCR is fairly smaller than those of methoxyphenyl, tolyl, ethylenic and carbonyl fragments, the two unpaired electrons localize on neither the methoxyphenyl, nor the tolyl, nor the ethylenic, nor the carbonyl fragment.…”

Section: Magnetic Properties Of the T 1 Statementioning

confidence: 99%

Photoexcited Singlet and Triplet States of a UV Absorber Ethylhexyl Methoxycrylene

Kikuchi

Hata

Kumasaka

et al. 2012

Photochem & Photobiology

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The excited states of UV absorber, ethylhexyl methoxycrylene (EHMCR) have been studied through measurements of UV absorption, fluorescence, phosphorescence and electron paramagnetic resonance (EPR) spectra in ethanol. The energy levels of the lowest excited singlet (S1) and triplet (T1) states of EHMCR were determined. The energy levels of the S1 and T1 states of EHMCR are much lower than those of photolabile 4-tert-butyl-4'-methoxydibenzoylmethane. The energy levels of the S1 and T1 states of EHMCR are lower than those of octyl methoxycinnamate. The weak phosphorescence and EPR B(min) signals were observed and the lifetime was estimated to be 93 ms. These facts suggest that the significant proportion of the S1 molecules undergoes intersystem crossing to the T1 state, and the deactivation process from the T1 state is predominantly radiationless. The photostability of EHMCR arises from the (3)ππ* character in the T1 state. The zero-field splitting (ZFS) parameter in the T1 state is D** = 0.113 cm(-1).

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The lowest triplet state of toluene by microwave induced delayed phosphorescence

Cited by 23 publications

References 21 publications

Distortion dependent intersystem crossing: A femtosecond time-resolved photoelectron spectroscopy study of benzene, toluene, and p-xylene

Distortion dependent intersystem crossing: A femtosecond time-resolved photoelectron spectroscopy study of benzene, toluene, and p-xylene

Optical and Time-Resolved Electron Paramagnetic Resonance Studies of the Excited States of a UV-B Absorber (4-Methylbenzylidene)camphor

Photoexcited Singlet and Triplet States of a UV Absorber Ethylhexyl Methoxycrylene

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