Light-Induced Hydrogen Abstraction from Isobutanol by Thienyl Phenyl, Dithienyl, and Thienyl Pyridyl Ketones

Ortica, F.; Romani, A.; Favaro, Giovanna

doi:10.1021/jp983839y

Cited by 20 publications

(11 citation statements)

References 28 publications

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“…The lifetime of this transient species is hundreds of nanoseconds in air-equilibrated solution and tens of microseconds in nitrogen-purged solutions (Table ). The same transient absorption signals could be produced by energy transfer in sensitization experiments where 2,2′-dithienyl ketone (DTK) − was employed as the high-energy triplet donor and NPI-PTZ1 / NPI-PTZ3 were employed as the triplet energy acceptors (see Figures S28–S30). The oxygen effect on the lifetime and the sensitization experiments demonstrate that the revealed transient absorption is relative to the T 1 state.…”

Section: Results and Discussionmentioning

confidence: 82%

Tuning the Fluorescence and the Intramolecular Charge Transfer of Phenothiazine Dipolar and Quadrupolar Derivatives by Oxygen Functionalization

et al. 2021

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A series of new naphthalimide and phenothiazine-based push−pull systems (NPI-PTZ1−5), in which we structurally modulate the oxidation state of the sulfur atom in the thiazine ring, i.e., S(II), S(IV), and S(VI), was designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction. The effect of the sulfur oxidation state on the spectral, photophysical, and electrochemical properties was investigated. The steady-state absorption and emission results show that oxygen functionalization greatly improves the optical (absorption coefficient and fluorescence efficiency) and nonlinear optical (hyperpolarizability) features. The cyclic voltammetry experiments and the quantum mechanical calculations suggest that phenothiazine is a stronger electron donor unit relative to phenothiazine-5-oxide and phenothiazine-5,5-dioxide, while the naphthalimide is a strong electron acceptor in all cases. The advanced ultrafast spectroscopic measurements, transient absorption, and broadband fluorescence up conversion give insight into the mechanism of photoinduced intramolecular charge transfer. A planar intramolecular charge transfer (PICT) and highly fluorescent excited state are populated for the oxygen-functionalized molecules NPI-PTZ2,3 and NPI-PTZ5; on the other hand, a twisted intramolecular charge transfer (TICT) state is produced upon photoexcitation of the oxygen-free derivatives NPI-PTZ1 and NPI-PTZ4, with the fluorescence being thus significantly quenched. These results prove oxygen functionalization as a new effective synthetic strategy to tailor the photophysics of phenothiazine-based organic materials for different optoelectronic applications. While oxygen-functionalized compounds are highly fluorescent and promising active materials for current-to-light conversion in organic light-emitting diode devices, oxygen-free systems show very efficient photoinduced ICT and may be employed for light-to-current conversion in organic photovoltaics.

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Section: Results and Discussionmentioning

confidence: 82%

Tuning the Fluorescence and the Intramolecular Charge Transfer of Phenothiazine Dipolar and Quadrupolar Derivatives by Oxygen Functionalization

et al. 2021

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“…The results with the two fluoroalcohols (Table ) and tert -butyl alcohol are rather similar. The latter weakly nucleophilic polar solvents favor H bonds to oxygen and stabilize excited π,π states and ions …”

Section: Discussionmentioning

confidence: 99%

“…The organic solvents as additives were acetonitrile, tert -butyl alcohol, 2,2,2-trifluoroethanol (TFE) or 1,1,1,3,3,3-hexafluoro-2-propanol (HFP). These fluoroalcohols are weakly nucleophilic and strongly polar solvents . A series of quinones, such as parent BQ, MeBQ, 2,5-, 2,6-Me 2 BQ, trimethyl-1,4-benzoquinone (Me 3 BQ), Me 4 BQ, 2,6-dimethoxy-BQ [(OMe) 2 BQ], and phenyl-BQ (PhBQ), were chosen.…”

Section: Introductionmentioning

confidence: 99%

Photoprocesses of p-Benzoquinones in Aqueous Solution

Görner

2003

J. Phys. Chem. A

104

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The photochemistry of 1,4-benzoquinone (BQ) and several derivatives, for example, duroquinone, trimethyl-2,5- or 2,6-dimethyl-, and methyl-BQ in aqueous solution or mixtures with polar media, for example, acetonitrile or 2,2,2-trifluoroethanol, was studied by time-resolved UV−vis spectroscopy after pulses at 248 and 308 nm. The triplet state and the semiquinone radical (•QH/Q•-) of BQs are spectroscopically and kinetically separated intermediates. The radical yield in the absence of H-atom donors is low and significantly increased in the presence of alcohols. Efficient photoinduced charge formation, because of Q•- and H+ after H-atom transfer from 2-propanol to the triplet state, and small effects in the absence of a donor were observed by transient conductivity. The quantum yield of photodecomposition, λirr = 254 nm, is substantial for BQ, MeBQ, and Me2BQs in aqueous solution, but small for Me4BQ. To account for the efficient photoconversion of BQs into hydrobenzoquinones and 2-hydroxy-1,4-benzoquinones, a novel water-mediated reaction not involving free radicals is proposed as major step. This mechanism is consistent with the prediction that the observed triplet state is monomeric and the yield of Q•-, detected by both transient absorption and conductivity, is low for sub-millimolar BQ, MeBQ, and Me2BQs at pH 5−6. In addition, H-atom abstraction from a polar organic solvent or by self-quenching plays a role in mixtures with water or at enhanced quinone concentration, respectively.

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“…The experimental setup was calibrated by an optically matched solution of benzophenone (f T = 1 and e T = 6500 m À1 cm À1 at the corresponding absorption maximum) in AcN. [48] Triplet-triplet absorption coefficients (e T ) were determined by energy transfer from DTK in CH (e T = 5200 m À1 cm À1 at l max = 630 nm) [49,50] for 2 and 4-6 and to D2TO in CH (e T = 53000 m À1 cm À1 at l max = 465 nm) [51] for 1 and 3.…”

Section: Methodsmentioning

confidence: 99%

Comprehensive Photophysical Behaviour of Ethynyl Fluorenes and Ethynyl Anthracenes Investigated by Fast and Ultrafast Time‐Resolved Spectroscopy

et al. 2012

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Detailed investigations by time-resolved transient absorption and fluorescence spectroscopies with nano- and femtosecond time resolutions are carried out with the aim of characterising the lowest excited singlet and triplet states of three ethynyl fluorenes (1-3) and three ethynyl anthracenes (4-6) in solvents of different polarity. The solvent is found to modify the deactivation pathways of the lowest excited singlet state of compounds 1-4, thus changing their fluorescence, intersystem crossing and internal conversion efficiencies. The fluorescence and triplet yields gradually decrease, while the internal conversion quantum yield increases upon increasing the solvent dielectric constant. These experimental results, coupled with the marked fluorosolvatochromic effect, point to the involvement of an emitting state with a charge-transfer (CT) character, strongly stabilised by polar solvents. This is proved by ultrafast spectroscopic studies in which two transients, distinguished by characteristic spectral shapes assigned to locally excited (LE) and CT states, are detected, the CT state being the longer lived and fluorescent one in highly polar solvents. The intramolecular LE→CT process, operative in highly polar media, becomes particularly fast (up to ≈300 fs) in the case of the NO(2) derivative 1. No push-pull character is found for 5 and 6, which exhibit different photophysical behaviour; indeed, the solvent polarity does not modify significantly the dynamics of the lowest excited singlet states. Quantum mechanical calculations at the TDDFT level are also used to determine the state order and nature of the lowest excited singlet and triplet states and to rationalise the different photophysical behaviour of fluorine and anthracene derivatives, particularly concerning the intersystem crossing process.

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Light-Induced Hydrogen Abstraction from Isobutanol by Thienyl Phenyl, Dithienyl, and Thienyl Pyridyl Ketones

Cited by 20 publications

References 28 publications

Tuning the Fluorescence and the Intramolecular Charge Transfer of Phenothiazine Dipolar and Quadrupolar Derivatives by Oxygen Functionalization

Tuning the Fluorescence and the Intramolecular Charge Transfer of Phenothiazine Dipolar and Quadrupolar Derivatives by Oxygen Functionalization

Photoprocesses of p-Benzoquinones in Aqueous Solution

Comprehensive Photophysical Behaviour of Ethynyl Fluorenes and Ethynyl Anthracenes Investigated by Fast and Ultrafast Time‐Resolved Spectroscopy

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