Several binuclear oxovanadium compounds of binucleating ligands are synthesised and investigated by magnetic, spectral and esr methods. The experimental results show that there is weak exchange interaction mediated by the bridging organic molecules between the vanadium centres. The magnitude of this interaction is more than that observed in the corresponding copper(II) dimers. The possible reason for this is discussed.

New photoresponsive azobenzene systems L¹–L¹⁰ have been synthesised and characterised. On irradiation at ∼330 nm, they undergo conversion fromE toZ form to a varying extent, depending on the nature and position of substitution on the azobenzene rings. They revert toE form in the dark. Photochemical equilibria have been studied in acetonitrile,o-dichlorobenzene and DMF.E forms are stabilized more ino-dichlorobenzene than in acetonitrile. Two of the molecules L¹ and L⁵ show enhanced transport of Cu²⁺ ions across liquid membrane on irradiation. Compounds L² and L³ undergoE→Z photoisomerisation on irradiation at ∼330 nm accompanied by fluorescence enhancement.Z→E isomerisation in the dark is accompanied by decrease in the fluorescence intensity. These are the first reported examples of fluorescence enhancement onE→Z isomerisation across N=N bond. Protonation of azo groups in L² and L³ is accompanied by fluorescence enhancement. The origin of the fluorescence enhancement in thecis isomer is explained on the basis of the inhibition of photoinduced electron transfer due to the nonplanar geometry of this isomer which reduces the effective conjugation of the nitrogen lone pair electrons with theπ electrons of the fluorophore.