The Triplet State and Molecular Electronic Processes in Organic Molecules

Lower, Stephen; El‐Sayed, M. A.

doi:10.1021/cr60240a004

Cited by 999 publications

(664 citation statements)

References 214 publications

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“…For the configuration of the lowest nπ * singlet and lowest ππ * triplet, in accordance with the Lower and El-Sayed rule [26], the intersystem crossing populates effectively the lowest triplet state and consequently, the intense phosphorescence is observed. Indeed, in nonpolar or weakly polar frozen solvents, CDA emits exclusively or predominantly phosphorescence [26,27].…”

Section: Discussionsupporting

confidence: 66%

The Geometry of the Excited Charge Transfer States: Flattening or Twisting?

Dobkowski

Sazanovich

2007

Acta Phys. Pol. A

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Numerous molecules built of an electron acceptor and electron donor units linked together by single bond exhibit a peculiar behavior in their low-lying electronically excited states. N,N-diethylaminoacetophenone and 4-acetyl-4 -dimethylamino-biphenyl, having acetophenone as the acceptor and differentiated by the donors groups N(CH3)2 and dimethylaniline, respectively, were selected as the subject of study. To recognize the excited state relaxation paths the stationary and time-resolved spectroscopy in absorption and emission was applied. Experimental results indicate that after excitation in polar solvents N,N-diethylaminoacetophenone reduces to minimum the overlap between π-electron systems of the donor and acceptor groups relaxing to the twisted internal charge-transfer state; contrary to that, flattening of the 4-acetyl-4 -dimethylamino-biphenyl skeleton generates increase in the overlap of the π-electron systems.

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Section: Discussionsupporting

confidence: 66%

The Geometry of the Excited Charge Transfer States: Flattening or Twisting?

Dobkowski

Sazanovich

2007

Acta Phys. Pol. A

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“…Phosphorescence spectra of ketones with n-π* nature of the lowest triplet state are usually structured, due to the vibrational progression of the CdO vibration, and π-π* triplets are mostly unstructured. 22,23 In addition, the phosphores- cence lifetime for n-π* triplets are significantly shorter (in the order of several milliseconds) compared to π-π* triplets (more than 100 ms). 23,24 Thus, the broad structureless phosphorescence of TX-S-CH 2 -COOH, together with the long phosphorescence lifetime, i.e., 127 ms in a matrix at 77 K, indicates a π-π* nature of the lowest triplet state.…”

Section: Resultsmentioning

confidence: 99%

Mechanistic Study of Photoinitiated Free Radical Polymerization Using Thioxanthone Thioacetic Acid as One-Component Type II Photoinitiator

et al. 2005

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A mechanistic study concerning photoinitiated free radical polymerization using thioxanthone thio-acetic acid (TX-S-CH 2-COOH) as one-component Type II photoinitiator was performed. Steady-state and time-resolved fluorescence and phosphorescence spectroscopy, as well as laser flash photolysis was employed to study the photophysics and photochemistry of TX-S-CH 2-COOH. The initiator undergoes efficient intersystem crossing into the triplet state and the lowest triplet state posseses π-π* configuration. In contrast to the unsubstituted thioxanthone, TX-S-CH 2-COOH shows an unusually short triplet lifetime (65 ns) indicating an intramolecular reaction. From fluoroscence, phosphorescence, and laser flash photolysis studies, in conjunction with photopolymerization experiments, we propose that TX-S-CH 2-COOH triplets undergo intramolecular electron transfer followed by hydrogen abstraction and decarboxylation producing alkyl radicals, which are the active initiator radicals in photoinduced polymerization. At low initiator concentrations (below 5 × 10 -3 M) this intramolecular reaction is the dominant path. At concentrations above 5 × 10 -3 M, however, the respective intermolecular reactions may be operative.

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“…On the other hand, the inclusion of a nitrogen atom into an aromatic system enhances the spin-orbit coupling and accelerates ISC. [38][39][40][41] In total, the values of k IC for these compounds are by order of magnitude lower than for KN, and the ISC to the triplet state plays an important role in the S 1 state decay, especially for KNA and 4HQN. XAN is an exception among the decomposition products of KN: its singlet excited-state lifetime in aqueous solution is even shorter than that for KN (Table 2), the population of the triplet state has not been detected, 17 and the photostability under anaerobic conditions is very high.…”

Section: Photochemical and Photobiological Sciences Papermentioning

confidence: 90%

Photochemistry of aqueous solutions of kynurenic acid and kynurenine yellow

Zelentsova

Sherin

Snytnikova

et al. 2013

Photochem Photobiol Sci

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The photophysics and photochemistry of kynurenic acid (KNA) and kynurenine yellow (KNY) in neutral aqueous solutions were investigated using time-resolved optical spectroscopy. Both molecules have similar quinoline-like structures, the only difference being the absence of conjugation in the nitrogen containing cycle in KNY. The main channel of S 1 excited state decay in the case of partially-unconjugated KNY is the solvent assisted S 1 → S 0 radiationless transition via intermolecular hydrogen bonds (Φ IC = 0.96), whereas, in the case of fully-conjugated KNA, it is intersystem crossing to the triplet state (Φ T = 0.82). The major intermediate products of the singlet excited KNY deactivation are the triplet state (Φ T = 0.022) and, most probably, the enol form (Φ enol = 0.012), which decay with the formation of 2,3-dihydro-4-hydroxyquinoline and 4-hydroxyquinoline, respectively. The results obtained show that KNA and KNY, which are products of the decomposition of the UV filter kynurenine, are significantly more photoactive and less photostable than the parent molecule.

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The Triplet State and Molecular Electronic Processes in Organic Molecules

Cited by 999 publications

References 214 publications

The Geometry of the Excited Charge Transfer States: Flattening or Twisting?

The Geometry of the Excited Charge Transfer States: Flattening or Twisting?

Mechanistic Study of Photoinitiated Free Radical Polymerization Using Thioxanthone Thioacetic Acid as One-Component Type II Photoinitiator

Photochemistry of aqueous solutions of kynurenic acid and kynurenine yellow

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