Kinetics of C–C and C–H Bond Cleavage in Phenyl Alkane Radical Cations Generated by Photoinduced Electron Transfer

Cyr, D. R.; Das, P. K.

doi:10.1021/jp508556z

Cited by 5 publications

(3 citation statements)

References 89 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To avoid the potential interference from transients originated by excitation of accumulating photoproducts, all pump–probe measurements were carried out in a single pass flow system that assures the presence of unreacted sample in the excitation volume with the laser operating at one pulse every 3 s. Measurements carried out in MeCN solution helped us confirm the identity of the transient absorption obtained in the case of 1a , which as reported in the literature, occurs in the 320–350 nm region with a λ max = 330 nm and is assigned to free diphenylmethyl radicals (Figure ). Similar measurements carried out in solution with all other ketones revealed similar results with λ max varying from 320 nm in the case of the fluoro-derivative 1e to 350 nm in the case of the methoxy compound 1d (Table ). A bathochromic shift of the respective λ max of the ketones 1a – 1e that follows the order 1e (F) < 1a (H) < 1c (Cl) = 1b (Me) < 1d ( OMe).…”

Section: Results and Discussionsupporting

confidence: 66%

Generation and Reactivity Studies of Diarylmethyl Radical Pairs in Crystalline Tetraarylacetones via Laser Flash Photolysis Using Nanocrystalline Suspensions

et al. 2017

View full text Add to dashboard Cite

The nanosecond electronic spectra and kinetics of the radical pairs from various crystalline tetraarylacetones were obtained using transmission laser flash photolysis methods by taking advantage of aqueous nanocrystalline suspensions in the presence of submicellar CTAB, which acts as a surface passivator. After showing that all tetraarylacetones react efficiently by a photodecarbonylation reaction in the crystalline state, we were able to detect the intermediate radical pairs within the ca. 8 ns laser pulse of our laser setup. We showed that the solid-state spectra of the radical pairs are very similar to those detected in solution, with λ in the 330-360 nm range. Kinetics in the solid state was observed to be biexponential and impervious to the presence of oxygen or variations in laser power. A relatively short-lived component (0.3-1.7 μs) accounts for only 3-8% of the total decay with a longer-lived component having a time constant in the range of 40-90 μs depending on the nature of the substituents.

show abstract

Section: Results and Discussionsupporting

confidence: 66%

Generation and Reactivity Studies of Diarylmethyl Radical Pairs in Crystalline Tetraarylacetones via Laser Flash Photolysis Using Nanocrystalline Suspensions

et al. 2017

View full text Add to dashboard Cite

show abstract

“…After selective excitation of [Zn( m -L) 2 ] at 420 nm in the presence of excess TCB, the resulting UV–vis transient absorption difference spectrum (Figure b) is essentially a 1:1 superposition of the spectral signatures of TCB •– (Figure a) , and [Zn( m -L) 2 ] + (Figure c). The latter resembles very closely the typical spectral signatures of triarylammonium radical cations, in line with the fact that the primary oxidation of [Zn( m -L) 2 ] occurs on the triarylamine unit of the chelate ligand.…”

Section: Results and Discussionmentioning

confidence: 99%

Zinc(II) Complexes with Triplet Charge-Transfer Excited States Enabling Energy-Transfer Catalysis, Photoinduced Electron Transfer, and Upconversion

Kübler

Pfund

Wenger

2022

JACS Au

View full text Add to dashboard Cite

Many CuI complexes have luminescent triplet charge-transfer excited states with diverse applications in photophysics and photochemistry, but for isoelectronic ZnII compounds, this behavior is much less common, and they typically only show ligand-based fluorescence from singlet π–π* states. We report two closely related tetrahedral ZnII compounds, in which intersystem crossing occurs with appreciable quantum yields and leads to the population of triplet excited states with intraligand charge-transfer (ILCT) character. In addition to showing fluorescence from their initially excited 1ILCT states, these new compounds therefore undergo triplet–triplet energy transfer (TTET) from their 3ILCT states and consequently can act as sensitizers for photo-isomerization reactions and triplet–triplet annihilation upconversion from the blue to the ultraviolet spectral range. The photoactive 3ILCT state furthermore facilitates photoinduced electron transfer. Collectively, our findings demonstrate that mononuclear ZnII compounds with photophysical and photochemical properties reminiscent of well-known CuI complexes are accessible with suitable ligands and that they are potentially amenable to many different applications. Our insights seem relevant in the greater context of obtaining photoactive compounds based on abundant transition metals, complementing well-known precious-metal-based luminophores and photosensitizers.

show abstract

“…As shown by us in a recent study [52], the radical-cation of DPME produced as a result of electron transfer from it to TCB singlet excited state underwent deprotonation to Ph 2 CH Á with a first-order rate constant of 1.5 9 10 6 s -1 . …”

Section: Resultsmentioning

confidence: 69%

Quenching of diphenylmethyl radical fluorescence by cyanoaromatics and phenols

Cyr

Das

2015

Res Chem Intermed

Self Cite

View full text Add to dashboard Cite

We have used double-laser nanosecond laser flash photolysis to study the kinetics of bimolecular quenching of the lowest doublet excited state of the transient diphenylmethyl radical ( 2 Ph 2 CH Á ) in acetonitrile at 25°C. We chose a series of cyanoaromatic compounds as acceptor-type quenchers and a series of 4-substituted phenols as donor-type quenchers. The observed bimolecular quenching rate constants (k Q ) are in the range 2 9 10 6 -2 9 10 10 M -1 s -1 for cyanoaromatics and 1 9 10 5 -3 9 10 9 M -1 s -1 for phenols. The Hammett plots of the k Q values for these two series have positive and negative slopes, respectively, and establish the enhanced behavior of the photo-excited diphenylmethyl radical as both a donor and an acceptor. For cyanoaromatics, the trend in the dependence of 2 Ph 2 CH Á * quenching rate constants on the free energy change of electron transfer (DG el ) coincides well with that of RehmWeller data on acceptor-type and donor-type quenchers of singlet excited states. An approximate fit of the k Q data for cyanoaromatics to the Agmon-Levine model of electron transfer gave a value of 4.5 kcal mol -1 for the free energy of activation at DG el = 0. For phenols, the trend in the dependence of k Q on the free energy change of electron transfer deviates significantly from that of cyanoaromatics data. This deviation was traced to the use of irreversible oxidation potentials of phenols to calculate DG el . No isotope effect is observed from substitution of phenolic hydrogen by deuterium, i.e., k Q,H /k Q,D & 1. Phenolate ions quench 2 Ph 2 CH Á * with large rate constants, 1-2 9 10 10 M -1 s -1 , i.e., well in the limit of diffusion control.

show abstract

Kinetics of C–C and C–H Bond Cleavage in Phenyl Alkane Radical Cations Generated by Photoinduced Electron Transfer

Cited by 5 publications

References 89 publications

Generation and Reactivity Studies of Diarylmethyl Radical Pairs in Crystalline Tetraarylacetones via Laser Flash Photolysis Using Nanocrystalline Suspensions

Generation and Reactivity Studies of Diarylmethyl Radical Pairs in Crystalline Tetraarylacetones via Laser Flash Photolysis Using Nanocrystalline Suspensions

Zinc(II) Complexes with Triplet Charge-Transfer Excited States Enabling Energy-Transfer Catalysis, Photoinduced Electron Transfer, and Upconversion

Quenching of diphenylmethyl radical fluorescence by cyanoaromatics and phenols

Contact Info

Product

Resources

About