Photoluminescence emission enhancement and coordination-driven isomer-locking effects of Cr(III) on azobenzene-bearing tweezer anchored to binaphthdiaza-crown macrocycles

In this report, the synthesis of a new bi-macrocycle tweezer linked through an azobenzene moiety, L was undertaken. The characterization of the tweezer was accomplished by employing IR, H-1 and C-13 NMR, UV-vis, fluorescence spectroscopy and CHN microanalysis while the UV-visible spectroscopy illustrated a trans reversible arrow cis photo-isomerization for L. According to our preliminary fluorescence observations, a metal-ion chemosensing behavior was established for trans-L isomer towards Cr(III) ion among the library metal ions. The quenching of the respective trans reversible arrow cis isomerization in the presence of Cr(III) ion suggested the preference of a strong interaction between Cr(III) ion with L, leading to isomer-locking of the trans-L isomer. Since the Job plots for L in the presence of Cr(III) metal ion suggested a 1:2 ratios for the interaction of Cr(III) with L, an electronic effect of Cr(III) ion with the phenolic groups on L was suggested as the main factor for the observed isomer-locking process in trans-L. The binding constant and the detection limit for Cr(III) ion by L were also assessed as 1.55 x 10(-8) M-1 and 10(-8) M, respectively, suggesting L as a new chemosensor for Cr(III) metal ion.