Electronic Absorption Spectra of Planar, Conjugated Biradicals in the Lowest Triplet State

Gisin, M. A.; Wirz, Jakob

doi:10.1002/hlca.19830660523

Cited by 24 publications

(10 citation statements)

References 65 publications

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“…The first intense triplet absorption band observed in the flash photolysis experiment of 1 lies to the blue of the first ground-state absorption band, like those of the extended linear acenes. This finding agrees well with predictions for the triplet-triplet absorption spectrum of o-xylylene calculated by a semiempirical PPP SCF CI model [16]. The parity-forbidden T,(13B,)-T,(23B,) transition is calculated to lie at 2.4 eV (515 nm).…”

Section: E('l)evsupporting

confidence: 87%

ChemInform Abstract: Triplet Energy of 2,2‐Dimethylisoindene from Electron‐Energy‐Loss Spectroscopy and Photoinduced Triplet Energy Transfer.

et al. 1995

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The excited electronic states of 2,2-dimethylisoindene (1) have been studied by electron-energy-loss spectroscopy. Its vertical gas-phase triplet (13B2), and singlet (I'B2) excitation energies are 1.61 and 3.19 eV, respectively. The excited states are thus lowered by 0.49 eV and 1.21 eV, respectively, when compared to the corresponding states of (all-E)-octatetraene, which serves as a reference compound. These shifts are partially reproduced by ZINDO calculations. The spectra give no evidence for a 2'A, state below the 1 'B, state, but this lack of observation does not exclude its existence. The lowest triplet state T,(1) was further characterized by flash photolysis. T, (1)

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Section: E('l)evsupporting

confidence: 87%

ChemInform Abstract: Triplet Energy of 2,2‐Dimethylisoindene from Electron‐Energy‐Loss Spectroscopy and Photoinduced Triplet Energy Transfer.

et al. 1995

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“…If the twist of the C ar -CO bond in fact is closer to 90°, then the absorption spectrum of 3 3 should be nearly identical to that of the phenoxy radical. TDFT as well as open-shell PPP SCF CI calculations 13 predict that 3 3 (twisted by 27°) and the phenoxy radical should have rather similar absorption spectra. We could not locate a stationary point for the singlet biradical 1 3.…”

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confidence: 99%

The Photo-Favorskii Reaction of p-Hydroxyphenacyl Compounds Is Initiated by Water-Assisted, Adiabatic Extrusion of a Triplet Biradical

et al. 2008

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p-Hydroxyphenacyl is an effective photoremovable protecting group, not least due to the fast release of its substrates, accompanied by a photo-Favorskii rearrangement of compounds 1 to p-hydroxyphenylacetic acid (2) that is transparent down to 300 nm. First used for the release of ATP from 1 (X = ATP) a decade ago, 1 the reaction has been employed in a variety of fields as diverse as neurobiology, 2 enzyme catalysis, 3 and biochemistry. 4 The nature and timing of the bond-making and bond-breaking events have not been fully elucidated despite extensive experimental and theoretical efforts by our group 5 and others. 6,7 We now report observation of the primary photoproduct, the triplet biradical 3 3, and of a new side product, p-hydroxybenzyl alcohol (6), that is formed by decarbonylation of the putative spirodione intermediate 4 at moderate water concentrations (Scheme 1). Solvent kinetic isotope effect (SKIE) studies by nanosecond laser flash photolysis (LFP) provide significant information on the role of water in the photo-Favorskii rearrangement of p-hydroxyphenacyl diethyl phosphate 1a to p-hydroxyphenylacetic acid (2). Anderson and Reese first reported the intriguing photoreaction 1(X = Cl) → 2 + HCl and suggested that the skeletal rearrangement may proceed via a spirodione intermediate 4, 8 which has yet to be detected. Intersystem crossing (ISC) of diethyl phosphate 1a is very fast, k ISC = 4 × 10 11 s −1 , 5 and we have established that the rearrangement proceeds from the triplet state, T 1. 1,4b,5 This was confirmed by Phillips et al. 7a-c Hydroxylic solvents play a major role in the rearrangement. The lifetime of T 1 decreases from several μs in degassed, dry CH 3 CN to about 0.4 ns in aqueous CH 3 CN (50% by vol). 5,7c,d The lifetime of T 1 of 1a is further reduced to 100 ± 10 ps in 87% aqueous CH 3 CN (Figure 1) and to 63 ± 10 ps in wholly aqueous solution. This was the key to revealing that the decay of T 1 left weak absorptions at 445, 420, and 330 nm, which decayed with a somewhat longer lifetime of ca. 0.6 ns. Pump-probe spectra obtained with other derivatives of 1 with good leaving groups (1b,c: X = tosylate, mesylate) also displayed the transient species possessing

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“…The electronic transitions of 1 and 2 were calculated using PPP SCF CI methods for both the singlet and triplet manifolds. Reasonable agreement with experiment for 1 (Figure ) was achieved only for the singlet and only by inclusion of doubly excited configurations in the configuration interaction matrix.…”

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confidence: 99%

2,2-Dimethyl-2H-dibenzo[cd,k]fluoranthene, the First Kekulé Hydrocarbon with a Triplet Ground State

1997

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Electronic Absorption Spectra of Planar, Conjugated Biradicals in the Lowest Triplet State

Cited by 24 publications

References 65 publications

ChemInform Abstract: Triplet Energy of 2,2‐Dimethylisoindene from Electron‐Energy‐Loss Spectroscopy and Photoinduced Triplet Energy Transfer.

ChemInform Abstract: Triplet Energy of 2,2‐Dimethylisoindene from Electron‐Energy‐Loss Spectroscopy and Photoinduced Triplet Energy Transfer.

The Photo-Favorskii Reaction of p-Hydroxyphenacyl Compounds Is Initiated by Water-Assisted, Adiabatic Extrusion of a Triplet Biradical

2,2-Dimethyl-2H-dibenzo[cd,k]fluoranthene, the First Kekulé Hydrocarbon with a Triplet Ground State

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