Azo-based iminopyridine ligands: synthesis, optical properties, theoretical calculations and complexation studies

Azobased iminopyridine ligands and their rhenium metal complexes: Syntheses, spectroscopic, trans-cis photoisomerization and theoretical studies

“…The simulated UV-visible spectra of the considered ligands and complexes agree very well with the observed ones, when using the CAM-B3LYP functional, so that our discussion will be based on the CAM-B3LYP results only. This reliability of the CAM-B3LYP functional for the UV-visible spectra simulation has already been observed in the case of the ligands [8].…”

“…4) of the two ligands L1 and L2 and their corresponding metal complexes ReL1 and ReL2 were recorded in dichloromethane solution (~ C = 5.9.10 -5 M) at room temperature. As previously reported [8], ligand L1 exhibits two strong absorption bands at  = 266 nm and 438 nm that are assigned to the * and n* ( 1 ILCT) transitions together with a slight intramolecular charge transfer (ICT) from the donating dimethylamino donor to the [13]. We assume that, in ReL1, the two absorption bands corresponding to the 1 ILCT and 1 MLCT are superimposed.…”

“…In the case of ligand L2 [8] a strong absorption band around 380 nm assigned to -* and n-* transitions is observed. In the case of ReL2, because of the presence of a nitro electron withdrawing group in L2, the absorption band in the visible region is blue-shifted, by comparison with L2, while a broad absorption band, of lower intensity ( = 4500 L.mol -1 .cm -1 ) is observed in the visible region around max = 452 nm which is characteristic of a metal to ligand charge transfer (Re(d  ligand(*) 1 MLCT transition [13].…”

“…The assignments of the observed UV-visible bands of the free L1 and L2 ligands have been described in reference [8]. To consider the photoisomerization issue, the properties of the free L1 and L2 ligands are compared to those of their corresponding complexes, reminding that ligand L1 only undergoes the trans to cis isomerization.The first excited states of both L1 and L2 derive from transitions involving the diazo group, thus likely to trigger the trans-cis photoisomerization of the azobenzene group.…”

“…In the present paper, we aim to report on the synthesis and full characterization, including X-ray diffraction analysis, of two rhenium metal complexes. The focus of this work is on the trans-cis photoisomerization behavior of the free ligands, L1 and L2, (scheme 1) [8] and of the corresponding complexes ReL1 and ReL2. These studies are supported by DFT and TD-DFT computational studies that reveal the importance of relevant barriers on the potential energy surfaces in the S1 excited states, which involve conical intersection, for rationalizing the observed behaviours.…”