title: Swift photoswitching in a binuclear Zn(II) metallacycle relative to a salen-type ligand.
abstract: The synthesis, characterization and photoswitching behavior of a new salen type Schiff base N,N'-bis(2-hydroxy-5-phenylazobenzilidene)-2,4,6-trimethylbenzene-1,3-diamine (H₂L) and a binuclear zinc(ii) metallacycle [{Zn(L)}2·2H2O] (1) have been described. Both H₂L and 1 have been characterized by satisfactory elemental analyses, spectral (FT-IR, (1)H, (13)C NMR, ESI-MS, electronic absorption, emission) and electrochemical studies. Crystal structures of both H₂L and 1 have been authenticated by single crystal X-ray diffraction analyses. These exhibit trans-cis photoisomerization upon exposure to UV light (365 nm) and get back to a more stable trans-form after withdrawal of the light. Electronic absorption, emission, (1)H NMR and cyclic voltammetric studies revealed that trans-cis isomerization in metallacycle 1 is rather rapid (~5.0 s) relative to H₂L (~25 s) which has been supported by theoretical studies (DFT). Relatively fast photoisomerization in 1 compared to H₂L is facilitated by a small energy gap between HOMO levels of the trans- and cis-isomers. The percentage trans-cis conversion ratio for both H₂L and 1 has been evaluated (55-45, H₂L; 60-40%, 1) by (1)H NMR studies.
authors.affiliation: Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005, India. dspbhu@bhu.ac.in.
authors.forename: Amit
authors.initials: A
authors.lastname: Kumar
authors.forename: Rampal
authors.initials: R
authors.lastname: Pandey
authors.forename: Rakesh Kumar
authors.initials: RK
authors.lastname: Gupta
authors.forename: Veenu
authors.initials: V
authors.lastname: Mishra
authors.forename: Shaikh M
authors.initials: SM
authors.lastname: Mobin
authors.forename: Daya Shankar
authors.initials: DS
authors.lastname: Pandey