Photochemical synthesis of nitroxyl free radicals in the presence of vinyl monomers

The photochemical formation of an inhibitor in the presence of monomers and a photoinitiator offers the possibility of producing positive two-step photoresists. As inhibitor precursor sterically hindred amines have been used in the presence of air oxygen and Rose Bengal as oxidation photosensitizer. On irradiation with visible light (546 nm). stable nitroxyle radicals are formed, which act as strong inhibitors of free radical polymerization. Hexanediol diacrylate and 2-acryloxy-2′-propionyl oxydiethylether were used as monomers. The photoinitiator required for the second step polymerization is benzoin isopropyl ether, which photolyzes on irradiation at 340 n,. The quantum yield of nitroxyl radical formation has been determined in solution and in polymeric films. Polymerization inhibition experiments were carried out with methyl methacrylate in solution and with neat monomers. Though the quantum yield Φ_NO° is low, especially in the last case, the experiments confirm the possibilities of this two-step procedure.     

Photochemical desulfurization of l-cysteine derivatives

Thiol groups can be reductively eliminated at room temperature by a photochemical method which makes use of triethylboron, triethylphosphite and visible light. Thus, after treating l-Cys 1a, d-Pen 1b, l-Cys-OMe 1c and glutathione (γ-l-Glu-l-Cys-Gly) 3, the corresponding desulfurized compounds l-Ala 2a, d-Val 2b, l-Ala-OMe 2c and γ-l-Glu-l-Ala-Gly 4, respectively, are prepared in high yields and with retention of configuration.     

Photochemical dynamics of indolylmaleimide derivatives

On-the-fly nonadiabatic ab initio molecular dynamics simulations have been carried out for three anionic species of indolylmaleimides (3-(1H-3-indolyl)-2,5-dihydro-1H-2,5-pyrroledione, IM) to clarify the mechanisms of photochemical reactions. The results are obtained for (i) a monovalent anion with a deprotonated indole NH group (IM(-)'), (ii) a monovalent anion with a deprotonated maleimide NH group (IM(-)') and (iii) a divalent anion with doubly deprotonated indole and the maleimide NH groups (IM(2-)). Quantum chemical calculations are treated at the three state averaged complete-active space self-consistent field level for 6 electrons in 5 orbitals with the cc-pVDZ basis set (CAS (6, 5) SCF/cc-pVDZ). Molecular dynamics simulations are performed with electronically nonadiabatic transitions included using the Zhu-Nakamura version of the trajectory surface hopping (ZN-TSH) method. It is found that the nonadiabatic transitions occur accompanied by the stretching and shrinking motions of the N(7)-C(8) bond in the case of IM(-)' and the C(11)-N(12) bond in IM(2-) rather than the twisting motion of the dihedral angle. We also found that the ultrafast S(2)→ S(1) nonadiabatic transitions occur through the conical intersection (CoIn) right after photoexcitation to S(2) in IM(-)' and IM(2-). Furthermore, the S(1)→ S(0) nonadiabatic transitions are found to take place in IM(-)'. It is concluded that IM(2-) would mainly contribute to the photoemission, because the S(1)← S(0) and S(2)← S(0) transitions of IM(-)' are dipole-forbidden transitions and, moreover, IM(2-) is found to be the only species to stay in the S(1) state without non-radiative decay.     

Synthesis of bifunctional derivatives of nitroxyl radicals of imidazoline

3-Imidazoline derivatives that contain a substituent with a functional group in the 2 position of the heteroring were obtained by the reaction of 1,2-hydroxyamino ketones with functionally substituted ketones and ammonia. The use of the reactivity of the endocyclic imino group makes it possible to accomplish the synthesis of a number of bifunctional derivatives of nitroxyl radicals of imidazoline and imidazolidine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 772–778, June, 1990.     

Photochemical synthesis of pentacene and its derivatives

A novel alpha-diketone precursor of pentacene, 6,13-dihydro-6,13-ethanopentacene-15,16-dione, was prepared and converted successfully to pentacene in 74 % yield by photolysis of the precursor in toluene: Irradiation of the diketone solution in toluene with light of 460 nm under an Ar atmosphere caused the solution to change from yellow to fluorescent orange-pink within a few minutes, after which, purple precipitates appeared. After 35 min, the solution changed to colorless and the purple precipitates were filtered to give pentacene in 74 % yield. By contrast, in the presence of oxygen, the color of the solution changed from yellow to pale yellow, and only 6,13-endoperoxide of pentacene was quantitatively obtained. The rate of the reaction upon photolysis was measured by observing the decay of n-pi* absorption of the precursor at 460 nm, and was found to be similar in both the presence and absence of oxygen. Therefore, the photoreaction of the alpha-diketone precursor seemed to occur via the singlet excited state. Because the T-T absorption of pentacene was observed upon photolysis of the precursor in the nanosecond transient absorption measurement under an Ar atmosphere, the excited triplet state of the pentacene generated singlet oxygen by sensitization, and it reacted with the ground-state pentacene to give the 6,13-endoperoxide. The alpha-diketone deposited on glass was also converted successfully to pentacene film by photoirradiation. In addition, diketone precursors of a mixture of 2,8- and 2,9-dibromopentacene and 2,6-trianthrylene were also prepared and their photoconversion was performed.     

Photochemical intramolecular nitrene insertion of 6-azidouridine derivatives

A highly efficient intramolecular nitrene insertion was observed upon irradiation of 6-azidouridine derivatives. The N⁶,2′-cyclo structure of the product was determined unequivocally by X-ray crystallography.     

Photochemical dimerization of p-benzoquinone methyl derivatives in crystals

Photochemical dimerization of p-benzoquinone and its methyl derivatives in crystals is discussed assuming that the reactivity is parallel with the stabilization energy of the transient complex. The calculation is carried out by taking both the terms of electronic structure of the monomer molecule and the intermolecular arrangement in the monomer crystal into consideration. Concerning the ability of photodimerization, the result obtained is qualitatively satisfactory. However, such an agreement with experiment cannot be obtained if either the electronic term or the geometrical term is ignored.

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Zusammenfassung Die photochemische Dimerisierung von p-Benzochinon und seines Methylderivates im Kristallzustand wird diskutiert; dabei wird angenommen, daß die Reaktivität parallel zur Stabilisierungsenergie des Übergangskomplexes ist. Die Berechnung wird so durchgeführt, daß sowohl die Elektronenstruktur des monomeren Moleküls als auch die Lage der Moleküle im Kristall des Monomeren berücksichtigt wird. Die Ergebnisse bezüglich der Fähigkeit zur Photodimerisierung sind qualitativ zufriedenstellend. Eine derartige Übereinstimmung mit dem Experiment kann jedoch nicht erhalten werden, wenn entweder der elektronische Beitrag oder der geometrische Beitrag vernachlässigt werden.

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Résumé La dimérisation photochimique de la p-benzoquinone et de ses dérivés méthylés dans les cristaux est discutée en supposant que la réactivité évolue parallèlement à l'énergie de stabilisation du complexe de transition. Le calcul est effectué en tenant compte de la structure électronique du monomère et de l'arrangement intermoléculaire dans le cristal du monomère. Le résultat obtenu est satisfaisant qualitativement en ce qui concerne la facilité de photodimérisation. Cependant, un tel accord avec l'expérience ne pourrait être obtenu si l'un des deux termes électronique ou géométrique était négligé.

     

Photochemical reaction of nitroanthracene derivatives in polymethyl methacrylate

Irradiation of 9-cyano-10-nitroanthracene or 9-benzoyl-10-nitroanthracene in polymethyl methacrylate (PMMA), at room temperature, gives the 9-cyano- or 9-benzoyl-10-anthryloxy radical which disappears slowly after irradiation, following the second order dark reaction, and finally gives the substituted anthranol. In the presence of TEA, the corresponding anthryloxy anions are obtained and their absorption spectra are greatly red-shifted compared with those in fluid basic polar solutions. The existence of 9-benzoyl-10-anthryloxy anion in basic PMMA is very interesting, because 9-benzoyl-10-anthranol is obtained in methyl methacrylate monomer (MMA) even in the presence of TEA. This is explained in terms of the increase of the microscopic medium polarity of MMA by the polymerisation.     

Photochemical polymerization of thiophene derivatives in aqueous solution

A novel method of photochemical polymerization of thiophene derivatives in aqueous solution catalyzed by potassium dichromate and initiated by illumination is described.     

Photochemical reactivities of photosensitive polymers containing chalcone derivatives

Monomeric vinyl chalcone derivatives were prepared by the condensation reaction of p-hydroxybenzaldehyde with acetophenone derivatives in the presence of sodium ethoxide as a base, followed by esterification of their hydroxy groups with methacryloyl chloride. The monomers, 4-(methacryloyloxy)chalcone derivatives, have been polymerized by a free radical technique. Copolymers containing the chalcone groups with different ratios of p-nitrophenylmethacrylate as photosensitizer group have also been prepared. The photosensitivities of the polymeric chalcone derivatives were investigated through their photochemical reaction on exposure to UV light, and by measuring the changes in their UV spectra before and after irradiation. The results obtained from the disappearance rates of the C?C bonds indicate that the photoreactivities of the polymers are largely affected by the position of the substituent in the phenyl ring of the chalcone, the photosensitizer group ratio, and the irradiation time.     

Photochemical reaction of carbazole and some derivatives in dichloromethane

By irradiation of carbazole and some derivatives in CH₂Cl₂ soln two different reaction pathways were observed depending on the substitution of the heterocyclic compound.     

Photochemical studies: Chromones,bischromones and anthraquinone derivatives

Photochemical reaction is a chemical reaction initiated by the absorption of energy in the form of light resulting in different types of reaction. Chromones, bischromones and anthraquinones are the bichromophoric molecules which contain the carbonyl group and double bond in conjugation. Photochemical reactions of these compounds result in the formation of such molecules which are not obtained via conventional methods. This review article describes the photochemical transformations of chromones, bischromones and anthraquinone derivatives and here main emphasis has been laid upon the intramolecular photochemical H-abstraction reactions that provide many exotic heterocyclics as the final photoproducts.     

Influence of nitroxyl radical center on keto-enol equilibrium of β-keto-esters of 3-imidazoline derivatives

Conclusions We used the keto-enol tautomerism of 4-carbomethoxyacetyl-3-imidazolines and 4-carbomethoxyacetyl-3-imidazoline 3-oxides and showed that in contrast to the radicals in the 3-imidazoline series, in the radicals of 3-imidazoline 3-oxide series, the spin effect of the radical center on the position of the tautomeric equilibrium is observed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 653–658, March, 1985.     

Photochemical properties and structures ofN-amino andN-azomethine derivatives of 2,4,6-triphenylpyridinium perchlorates

The molecular structures of the initial compounds and the products of photocyclization involving amino and azomethine groups in perchlorates ofN-amino (1) andN-azomethine (2) derivatives of 2,4,6-triphenylpyridinium cations were studied. Cations1 and2 have an essentially non-coplanar arrangement of the -Ph rings, and the product of photocyclization of2, cation3, is characterized by a flattened structure. It was found that the orientation of the lone electron pair of the N atom with respect to one of the planes of the -Ph rings in molecule1 is more favorable for monocyclization involving the amino group. The structure of molecule2 allows two routes of the photoreaction,viz., O N proton transfer and monocyclization with an -Ph ring. However, the structural features of molecule2 are more favorable for photocyclization.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 296–301, February, 1995.     

Conformational analysis of 2-anthryl-ethylene derivatives: Photochemical and computational investigation

2-Anthrylethylene derivatives 1 E?C5 E and 1 Z are synthesized to study the cis-trans photoisomerization. Interestingly, unlike 9-anthrylethylene derivatives, 2-anthrylethylene derivatives 1 E to 5 E do not exhibit E(trans) to Z (cis) photoisomerization upon direct and triplet sensitization. One-way Z (cis) to E (trans) photoisomerization of 1 Z is found to be very efficient under direct and triplet sensitization conditions, demonstrating the involvement of both singlet and triplet states. 1 E?C5 E exhibits excitation wavelength dependent fluorescence indicating the existence of conformers (rotamers) at room temperature, which is confirmed by fluorescence lifetimes measurements of compounds 1 E and 2 E. Theoretical studies are carried out at DFT and ab initio methodology and the calculated relative energy difference of the conformers is very small; it ranges between 2.9 kJ·mol^?1 to 6.3 kJ·mol^?1 for both ground and excited states.