Magnetic field effects upon photochemistry of bichromophoric chain molecules containing nitroaromatic and arylamino moieties: Elucidation of reaction mechanism and control of reaction yields

Abstract

This paper is dedicated to Professor Charles A. McDowell on the occasion of his 70th birthdayRYOICHI NAKAGAKI, KIYOSHI MUTAI, MITSUO HIRAMATSU, HIDEYUKI TUKADA, and SABURO NAKAKURA. Can. J. Chem. 66, 1989Chem. 66, (1988.The photochemistry of bichromophoric species containing nitroaromatic and arylamino moieties has been studied in the presence and absence of an external magnetic field. Photolysis products are an unsubstituted arylamine, a nitrosoaromatic species (Product I), and a nitroaromatic compound (Product 2). On application of the magnetic field, the formation yield for Product 1 decreases and that for Product 2 correspondingly increases, whereas the consumption of the starting material and the release of the unsubstituted arylamine are independent of the magnetic field. Analysis of the magnetic field effects shows that the hyperfine coupling mechanism predominates and that the photoreaction takes place in the triplet manifold of the nitroaromatic moiety. Application of the magnetic field may cause an appreciable change in the relative yield of cage and escape products, i.e., the branching ratio of competitive processes. (1988).On a etudie les effets du champ magnetique sur la photochimie des espkces bichromophoriques qui contiennent un groupement arylamink et un noyau nitroaromatique. Les produits de photolyse sont I'amine aromatique nonsubstituee, le compose aromatique nitrose (Produit l), et le compose aromatique nitre (Produit 2). Sous un champ magnetique, le rendement du Produit 1 est diminue et celui de Produit 2 est augmentt, tandis que la consommation de l'espttce de depart ou la liberation de I'amine aromatique nonsubstituee ne depend pas de l'intensitt du champ magnktique. De l'analyse des effets du champ magnetique, il resulte que le mecanisme du couplage hyperfin predomine et la reaction photochimique a lieu dans un etat triplet du noyau nitroaromatique. L'application du champ magnttique peut causer un changement manifeste dans la proportion des deux produits photochimiques de la reaction concurrente, c.-a-d., le produit de cage et celui de fuite.

Spin effects in intramolecular electron transfer in naproxen-N-methylpyrrolidine dyad

“…In the latter, the dependence of triplet yield on external magnetic field can be correlated with the value of average electron exchange coupling in a radical ion pair (RIP),H max ~ 2J 0 . The 2J 0 value of the majority of the investigated biradicals with a chain length of 6-10 carbon atoms, which is close to that in the NPX-PYR dyad, amounts to about 10-50 mT [25,29,30,31]. In this study the MFE was measured in the magnetic field range of up to 70 mT.…”

Spin Chemistry Investigation of Peculiarities of Photoinduced Electron Transfer in Donor–Acceptor Linked System

“…In the latter case the dependence of the triplet yield on external magnetic field will correlate with the value of the average electron exchange coupling in the radical ion pair (H max ~ 2J 0 ). The majority of experimentally observed values of J 0 are in the range of up to 1T [12,14,25,26]. The values of HFI constants and the difference of g-factors of the donor and acceptor fragments in discussed biradical ion let us also expect the appearance of MFE formed via the HFI and relaxation mechanisms [11].…”

“…Indeed, linked systems with different rigid or flexible spacers have proven to be good models to study the features of electron transfer processes. Note that most spin chemistry studies of linked systems (dyads and triads) were carried out using only magnetic field effects (MFE) [12,14]. The main information obtained from the analysis of magnetic field dependence concerns the energy of the electron exchange interaction between paramagnetic centers of dyads and triads.…”

Photochemistry of large ring 2-phenylcycloalkanone in the presence of molecular oxygen

“…In 1972, the photolysis of 2-phenylcyclopentanone (C 5 ) and 2-phenylcyclohexanone (C 6 ) have been reported by Baum, in which alkenals were obtained in high yields (>80%) [17]. Several years later, Doubleday has found that magnetic fields affect the CIDNP signals of 13 C carbonyl carbons of 2-phenylcycloalkanones (2PCAs) (C 6 -C 8 ) as well as photoproducts of alkenals and ketenes [3]. This result suggests that the ISC of acyl-benzyl biradicals is influenced by external magnetic fields.…”

“…We have recently reported that the triplet acyl-benzyl biradicals (C 6 -C 8 ) react with molecular oxygen to produce benzoylalkanoic acids, which can be further excited by the UV light, and then subsequent intramolecular hydrogen abstraction (Norrish Type Ⅱ) occurs to produce acetophenone and the corresponding alkenoic acids [18]. Turro et al have observed enhanced 13 C CIDNP signals at carbonyl carbon on the products in 3 the photolysis of 2-phenylcyclododecanone (2PCDD) in aerated solution, in which the presence of an oxidized peroxyester or peracid species has been suggested [6]. Interestingly, the 13 C CIDNP signal from carbon dioxide has been observed, which may be evolved by the decarboxylation on the peroxyester or peracid species in the 2PCDD photolysis.…”