Photochemical properties of the cyclopentadienyliron complex of phenothiazine

Abstract

Photolysis of [(η⁶-phenothiazine)(η⁵-cyclopentadienyl)]iron(II) hexafluorophosphate (1) has been examined in various solvents such as MeOH, DMSO, THF, MeCN, furan, CH₂Cl₂, CF₃CH₂OH and (CF₃)₂CHOH. Photoreactions are induced by excitation at λ= 254, 313, 337, 366, 514.5 and 647.5 nm. The major reaction leads to the photorelease of phenothiazine (2) which does not react further under the reaction conditions. Quantum yields of photolysis of 1, φ₍₁₎, and photorelease of 2, φ₍₂₎, are independent of concentration in the range of 1 × 10^–4–1 × 10^–2 mol dm^–3, wavelength of excitation and light intensity and in MeOH, MeCN, furan and THF, φ₍₁₎=φ₍₂₎=ca. 1. The quantum yields are lower in solvents of lower nucleophilicity and in CH₂Cl₂, CF₃CH₂OH and (CF₃)₂CHOH the φ₍₁₎ values are 0.45, 0.26 and 0.03, respectively. In some solvents ferrocene formation is also observed. Applying oxygen as a quencher it is found that photochemical decay of 1 takes place from the excited state ³E₁, with a lifetime of τ_³E1 < 10^–8 s and leads to formation of 2.