Carbazole-naphthoyl hydrazone conjugate and its Zn(II)-complex as stimuli-responsive smart materials: VOC and Cu2+ detection, AIE insights and bioimaging applications

Abstract

A readily accessible hydrazone (E)-N'-((9-ethyl-9H-carbazol-3-yl)methylene)-3-hydroxy-2-naphthohydrazide ligand (HL) and its luminescent Zn(II)-complex (1) have been synthesized and thoroughly characterized by several spectro-analytical techniques. Photophysical properties of HL and 1 have been explored both in the solid and solution states. Interestingly, HL displayed reversible mechanochromism under ambient light and reversible mechanofluorochromism under 365 nm UV irradiation, whereas its complex 1 does not show any sharp visual color change under ambient light, however, it exhibits noteworthy reversible mechanofluorochromism under 365 nm UV light (bright yellow to golden yellow). Besides solid-state UV/vis and photoluminescence spectroscopies, the underlying mechanism of phase transformation has further been explored by SEM, PXRD, and TGA/DSC analyses. As anticipated, 1 demonstrated remarkable J-type AIE characteristics in the THF/H2O mixture whereas H-type AIE in DMSO/H2O, corroborating well with UV/vis, luminescence techniques, and nanotracking (NTA) analysis. Further between HL and 1, only Zn(II)-complex effectively and selectively detects Cu2+ in aqueous DMSO media, and the limit of detection determined to be 9.1 × 10-7 M. Moreover, both HL and 1 were investigated for their biological applications and the MTT assay revealed 1 being less cytotoxic than HL on the MCF-7 breast cancer cell line. Further, 1 showed strong fluorescence in the cytosol of the cell compared to that of HL, hence it can be used as a cell staining agent. Overall, the present research findings could successfully demonstrate the straightforward mutual comparison as well as multifunctional behavior of HL and 1 for wider applications in environmental sensing, data storage devices, and bioimaging studies.