Novel luminescent β-ketoimine derivative of 2,1,3-benzothiadiazole: synthesis, complexation with Zn(ii) and photophysical properties in comparison with related compoundsElectronic supplementary information (ESI) available: Crystallographic data and additional figures. CCDC 1457754 (α-L2H), 1457755 (β-L2H), 1457756 (ZnL2). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6ra06547c

A novel β-ketoimine-functionalized 2,1,3-benzothiadiazole (4-(2,1,3-benzothiadiazole-4-ylamino)pent-3-en-2-one, L2H ) was synthesized and used as chelating ligand for the complexation with Zn( ii ) (complex ZnL2 ). The spectroscopic and photophysical properties of L2H and ZnL2 as well as those of previously described 4-amino-2,1,3-benzothiadiazole ( L1 ) and its complex ZnL1 have been thoroughly studied in the crystalline state and solution. The UV-Vis absorption spectra of free ligands L1 , L2H and its deprotonated form L2 − , and complexes ZnL1 and ZnL2 were assigned on the basis of TD-DFT calculations. In contrast to ZnL2 having conventional single-band fluorescence, ZnL1 demonstrates a broad double-band purple-white fluorescence spanning the entire visible region. On the basis of careful spectroscopic studies the second band of this unusual fluorescence spectrum was attributed to the presence of traces of free ligand L1 in the crystals of complex ZnL1 . The energy transfer from the excited state of ZnL1 to a free ligand L1 was revealed. 2,1,3-Benzothiadiazoles and their Zn complexes show fluorescence in different wavelength regions, one of the complexes reveals white emission.