Palladium(II)-iodo-{1-alkyl-2-(arylazo)imidazole} complexes: Synthesis, structure, dynamics of photochromism and DFT computation

[Pd(Raai-CnH2n+1)(2)I)](2)[Pd2I6} (Raai-CnH2n+1 = 1-alkyl-2-(arylazo)imidazole) has been characterized by the spectral data (UV-Vis, FfIR, Mass, H-1 NMR). The single crystal X-ray structure of [Pd(Meaai-C2H5)(2)I](2) [Pd2I6] shows that one Meaai-C2H5 acts as monodentate N(imidazoly1) donor, while the other one is bidentate N(imidazolyl), N(azo) chelator; the charge is neutralized with [Pd2I6](2-) anion. UV light irradiation in DMF solution of the complexes show trans-to-cis isomerisation of Raai-CnH2n+1 about -N=N- bond. Quantum yields (phi(t -> c)) of trans-to-cis isomerisation of the complexes are lower than that of the free ligand data. This observation is consistent with femtosecond transient absorption results of [Pd(Haai-C10H21)(2)][Pd2I6], which suggest that the trans -> cis isomerization occurs in the monodentate azo-imidazole group and the bidentate azo-imidazole, because of chelation with Pd(II), does not exhibit photochromism. The isomerization proceeds with a time constant of similar to 1.0 ps in acetonitrile, 0.6 ps in methanol, and 1.7 ps in ethylene glycol, which are comparable to those the free azo-imidazole ligand. In contrast, the reverse transformation, i.e. ds-to-trans, is carried out by thermal process and the activation energy (E-a) of cis-to-trans isomerisation of the complexes is lower than that of free ligand. The spectral property and photochromic efficiency have been explained by DFT computation of optimized geometry of the complex. (C) 2014 Elsevier Ltd. All rights reserved.