Photochemistry of carbocyanine alkyltriphenylborate salts: intra-ion-pair electron transfer and the chemistry of boranyl radicals

Kinetic study of free-radical polymerization photoinitiated by cyanine-borate salts. II.

“…3 Electron transfer from the borate anion to the singlet excited state of cyanine dye leads to the formation of radical cation [Cy ⅐ ϩ ] and the boranyl radical, which rapidly decomposes, yielding an alkyl radical able to initiate the polymerization of vinyl monomers.…”

“…From the literature, 3 it is known that the efficiency of [Cy ⅐] formation depends on the structure of the alkyl group bound to boron. For Cy ϩ [NpCH 2 B(Ph) 3 ] Ϫ , radical formation is very efficient; however, for Cy ϩ [Ph 4 B] Ϫ , there is no [Cy * ] formation.…”

“…The radicals formed might couple to form an alkylated cyanine, [Cy-R], or to diffuse from the initial solvent cage, giving free radicals. 3 A laser flash photolysis examination of the cyanine-borate salts shows that the electron-transfer reaction has two limiting outcomes. The borates capable of generating stabilized alkyl radicals (i.e., benzyl) give the [Cy ⅐ ] radicals with a high yield, and the electron-transfer process for these electron donors is faster than the back electrontransfer process.…”

Difluoroboranyl derivatives as efficient panchromatic photoinitiators in radical polymerization reactions

“…This observation shows that the light intensity has no effect on the quantum yield of free radical formation / [41] and suggests that the polymerization follows a typical radical chain mechanism with second-order termination [35]. It is well-known that the alkyl radical formed from borate salts as a results of the electron transfer from borate anion to the excited state of sensitizer leading to boranyl radical followed by its decomposition initiates radical polymerization of acrylates [42,43]. To study the photochemical process that occurs in the excited state of the difluoroboranyl complexes, the nanosecond laser flash photolysis was used.…”

The Comparison of the Photoinitiating Ability of the Dyeing Photoinitiating Systems Acting via Photoreducible or Parallel Series Mechanism

“…The work of Schuster and co-workers [19,20] on the photochemistry of cyanine borates led to the preparation of the color-tunable, operating in the visible region commercial photoinitiators [21]. This research group discovered that, photolysis of 1,4-dicyanonaphthalene containing an alkyltriphenylborate leads to one electron oxidation of alkyltriphenylborate salts yielding an alkyltriphenylboranyl radical that undergoes carbonboron bond cleavage and the formation of free radicals [22].…”