Photolysis of 1-Bromo-2,2-bis(p-methoxyphenyl)ethene in solution

Article abstract of DOI:10.1039/ft9928801385

UV irradiation (λ_inc = 254 nm) of 1-bromo-2,2-bis(p-methoxyphenyl)ethene (AAHVB) in acetonitrile solution results in its decomposition: Φ(-AAHVB) = 0.18 both in the absence and presence of O2.Apart from the isomers <(E)-1-bromo-1,2-bis(p-methoxyphenyl)ethene (HAAVB) and (Z)-1-bromo-1,2-bis(p-methoxyphenyl)ethene (AHAVB)> the main photoproducts are 1,2-bis(p-methoxyphenyl)ethine (P-2) and HBr (Φ ca. 0.1).Flash photolysis studies in acetonitrile, dichloromethane and n-hexane solution at 266 nm revealed that P-2 is formed with a halflife of less than a few ns via a singlet route involving vinyl cations which rapidly rearrange and split off protons.Part of the vinyl cations decay via a differnet route forming an ionic species with an optical absorption band at ca. 350 nm.The decay of the latter is not correlated with the formation of P-2.This ionic species probably results from an interaction of vinyl cations with solvent or AAHVB.AAHVB quenches triplet states of various compounds X (e.g. benzophenone, chrysene, benzil, pyrene) provided that E_T(X) >200 kJ mol^-1.The energy transfer from these compounds to AAHVB does not result in the formation of P-2 or vinyl cations.

Full text of DOI:10.1039/ft9928801385

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