Photolysis of benzyl halides and benzyl acetate in alcohols

Appleton, David C.; Brocklehurst, B.; McKenna, J.; McKenna, J. M.; Smith, Martin J.; Taylor, Paul S.; Thackeray, Stephen; Walley, Andrew R.

doi:10.1039/c39770000108

Cited by 11 publications

(5 citation statements)

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“…It should be noted that the photodissociation studied here is of the same type as the carbon-halogen bond cleavage of arylmethyl halides, a reaction that has been investigated in detail for a long time. [26][27][28][29][30][31] These systems are usually easier to study since they exhibit longer intrinsic lifetimes for both the S 1 and T 1 states, i.e., both states are emissive and can be observed directly. The main result derived from these studies is that in aprotic solvents these compounds undergo exclusively homolysis leading to radicals but heterolysis and homolysys in protic solvents.…”

Section: Resultsmentioning

confidence: 99%

Mechanistic Studies of Photoacid Generation from Substituted 4,6-Bis(trichloromethyl)-1,3,5-triazines

Pohlers¹,

Scaiano²,

Sinta³

et al. 1997

Chem. Mater.

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The photochemistry and photophysics of 2-methyl-(1), 2-(2′-furylethylidene)-( 2), and 2-[(4′methoxy)styryl]-4,6-bis(trichloromethyl)-1,3,5-triazine (3), three compounds that find application as photoacid generators in photoresist formulations, have been investigated under conditions of direct excitation and using various phenothiazine derivatives as photosensitizers. C-Cl bond cleavage is confirmed by laser flash photolysis as the primary photochemical step in the direct photolysis of these compounds; the chlorine atoms formed in this reaction can be detected by complexation with chloride anions or benzene. In the case of 1, this photodissociation occurs with a lifetime of <20 ns. The quantum yield of bond breaking for 1 after direct excitation as determined by laser flash photolysis and steady-state irradiations was found to be 30-40 times greater than for 2 and 3. The mechanism under sensitized conditions involves electron transfer from the excited phenothiazines to the triazines as the primary photochemical step; the rate constants for excited-state quenching exceed 10 9 M -1 s -1 for the T 1 state and 10 10 M -1 s -1 for the S 1 state. The rate constants correlate with the free energy for electron transfer estimated from the excited-state energies and the oxidation potential of the sensitizers.

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Section: Resultsmentioning

confidence: 99%

Mechanistic Studies of Photoacid Generation from Substituted 4,6-Bis(trichloromethyl)-1,3,5-triazines

Pohlers¹,

Scaiano²,

Sinta³

et al. 1997

Chem. Mater.

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“…trends are present for both the 1-naphthylmethyl and the benzyl [1][2][3][4][5][6][7] derivatives. It is, of course, difficult to interpret these results for direct irradiations since, as discussed briefly in the Intro-…”

Section: Introductionmentioning

confidence: 87%

“…[5] where +, is the reaction quantum yield, kr is the rate constant in question, and kd is the total rate of decay of the excited singlet state or the reciprocal of the lifetime 7,. The lifetimes of the substrates 4,5, 6, and 7 are directly measurable by single-photon counting of fluorescence decay; 1, 2, and 3 are too short-lived.…”

Section: Quantum Yields and Photofugacitiesmentioning

confidence: 99%

Homolytic versus heterolytic cleavage for the photochemistry of 1-naphthylmethyl derivatives

Arnold¹,

Donald²,

Jurgens³

et al. 1985

Can. J. Chem.

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Can. J. Chem. 63, 3140 (1985). The photochemical cleavage of the I-naphthylrnethyl derivatives, 1-7, has been examined in methanol solvent under both direct and sensitized conditions. The cornpetitition between hornolytic and heterolytic cleavage as a function of multiplicity and leaving group has been studied in detail. Only substrates 1, 2, 3, and 7 react on sensitization with xanthone but evidence is presented that the resulting reactivity of 1, 2, and 3 may not be triplet cnergy transfer but rather exciplex formation. A semi-quantitative scale for photofugacities of the leaving groups from the excited singlet states has been established. 3140 (1985). Utilisant le rnkthanol comrne solvant, on a Ctudit le clivage photochimique des dCrivCs du naphtyl-l mCthyle 1 h 7 tant dans conditions directes que sous I'influence de sensibilisateurs. On a soigneusernent CtudiC la compCtition entre les clivages hornolytique et hCtirolytique en fonction tant de la rnultiplicitC que du groupe labile. Seuls les substrats 1, 2, 3 et 7 reagissent lorsqu'on utilise le xanthone cornrne sensibilateur; toutefois, on prouve que la rCactivitC rksultante des dCrivCs 1, 2 et 3 n'est pas due h un transfert d'tnergie du triplet rnais plutBt h la formation d'un exciplex. On a Ctabli une Cchelle semi-quantitative des photofugacitCs des groupes labiles h partir des Ctats singulets cxcites.[Traduit par le journal] Introduction Since the initial reports by Zimmerman et nl. (1, 2) on the photocleavage of benzylic derivatives (ArCH2-X) in nucleophilic solvents, there has been considerable interest in this seemingly simple process. Much of the work has focused on the competition between homolytic versus heterolytic cleavage as a function of the multiplicity of the excited state (i.e. direct versus sensitized irradiations) and the nature of the photofugal

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“…Light-induced homolytic cleavage of the C–Br bond of PM may yield two different reactive intermediates (Scheme ): (i) radical intermediate 1 and (ii) cationic intermediate 3 . Evidence for both intermediates is found by performing the photolysis in alcoholic solution, which yields radical recombination products, such as a dimer, as well as benzylic ethers. , During the Gilch reaction, 1 may be incorporated as radical chain end, whereas 3 may convert into Q upon proton abstraction by base. In principle, the latter hypothetically poses the possibility of initiating the prepolymerization in the absence of a base.…”

Section: Results and Discussionmentioning

confidence: 99%

“…■ RESULTS AND DISCUSSION Premonomer Photolysis. Since benzyl radical fragments 43,44 resulting from UV-photolysis of PM might interfere with the Gilch reaction, we study the extent of this process prior to discussing the polymerization runs themselves. Lightinduced homolytic cleavage of the C−Br bond of PM may yield two different reactive intermediates (Scheme 2): (i) radical intermediate 1 and (ii) cationic intermediate 3.…”

Section: ■ Introductionmentioning

confidence: 99%

Full Quantification of the Light-Mediated Gilch Polymerization

et al. 2018

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Alkoxy-substituted poly(p-phenylenevinylenes) (PPVs) continue to be major workhorse materials in optoelectronics, ranging from thin film electronics to bioimaging. An attractive synthetic route toward PPVs is the Gilch polymerization. Nevertheless, obtaining control over molecular weight and chain constitution is challenging due to the free-radical nature of this reaction. In this work we quantitatively show with in situ UV-irradiation NMR spectroscopy how control over the Gilch polymerization can be enhanced by irradiation with UV-light. The potential of this method has been demonstrated but never interpreted within a quantitative framework, resulting in a lack of mechanistic and kinetic insight. We account for this not only by in situ analyzing and modeling the photochemical Gilch polymerization but also by characterizing the photolysis of the starting material. The latter shows that the solvent THF likely acts as radical transfer agent in the Gilch pathway and similar precursor-based biradical routes. We perform two photopolymerization runs: (i) under continuous UV-irradiation and (ii) by applying a short UV pulse while monitoring the chemical response of the mixture. Since existing models of the Gilch polymerization are inadequate for describing the recorded time−concentration profiles, we develop a new model that couples thermal and photoinduced polymerization. Numerical curve fitting quantifies the rate constants associated with both pathways. We demonstrate that (i) a photoactivated p-quinodimethane species Q* reacts in the (re)initiation and propagation steps, (ii) photopropagation is significantly faster than photoinitiation, and (iii) the photochemical reactions are considerably faster than their thermal analogues, which allows for decoupling the thermal and photochemical pathways at temperatures low enough to suppress the former.

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Photolysis of benzyl halides and benzyl acetate in alcohols

Cited by 11 publications

References 0 publications

Mechanistic Studies of Photoacid Generation from Substituted 4,6-Bis(trichloromethyl)-1,3,5-triazines

Mechanistic Studies of Photoacid Generation from Substituted 4,6-Bis(trichloromethyl)-1,3,5-triazines

Homolytic versus heterolytic cleavage for the photochemistry of 1-naphthylmethyl derivatives

Full Quantification of the Light-Mediated Gilch Polymerization

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