In cobalt(III) amine complexes containing amino acids, photolysis in the chargetransfer bands leads to the formation of alkyl cobalt(III) complexes. Steady and flash photolysis of complexes [Co(LL)₂X]²⁺ and [Co(LL)₂Y₂]⁺ (LL = ethylene diamine, polypyridyl or propylenediamine, X = amino acid and Y = nitro ligand) were carried out. Steady irradiation of [Co(bpy)₂(gly)]²⁺ ion (bpy = bipyridine, gly = glycine) in aqueous medium (pH 1–7) produces the six-coordinated complex [Co(bpy)₂(CH₂NH₂)]²⁺. Flash photolysis of the complex under identical conditions gives an alkyl complex. The alkyl complex formed in the case of [Co(bpy)₂(gly)]²⁺ ion is stable and could be isolated; the corresponding alkyl complex formed from [Co(bpy)(en)(gly)]²⁺ ion leads to the labilisation of the ethylenediamine ligand in acidic solutions. Photolysis of the nitro complexes of the type [Co(en)₂(NO₂)₂]⁺ ion in acetonitrile, methanol and ethanol produces aπ-bonded transient nitro complex which reacts with molecular oxygen to give the mononuclear superoxo, dinuclear superoxo and dinuclear peroxo complexes in sequence. The formation of these products from the free radical coordinated cobalt(II) complex has been followed by the flash photolysis method and the rate constants have been determined. The details of the mechanisms are discussed.

Time-dependent reorientations of resorcinol-based acridinidione (ADR) dyes in glycerol were studied using steady-state and time-resolved fluorescence studies. The difference between fluorescence anisotropy decays recorded at 460 nm when exciting at 250 nm and those obtained when exciting at 394 nm are reported. When exciting at 394 nm, the fluorescence anisotropy decay is bi-exponential, while on exciting at 250 nm a mono-exponential fluorescence anisotropy decay is observed. We interpret this in terms of different directions of the absorption dipole at 394 and 250 nm with the emission dipole respectively, which is experimentally validated and further analysed as a prolate model of ellipsoid.