Synthesis, Structure, and Halo‐, Photo‐, and Thermochromism Properties of 5‐Azotriazolyl Salicylic Acid and Its Cd II Complex

A hydrated 5‐azotriazolyl salicylic acid of [(H 3 ATSA)]⋅2 H 2 O ( 1 ) and its Cd II complex of [Cd 2 (H 2 ATSA) 4 ]⋅13 H 2 O ( 2 ) have been synthesized and characterized by single‐crystal X‐ray diffraction analysis and a neutral trans ‐ Z ‐enol form of H 3 ATSA and another anionic trans ‐ E ‐enol H 2 ATSA − isomer have been found in 1 and 2 , respectively. The yellow crystal of 2 can be transformed in situ into red crystals in NaOH solution. The diffuse reflectance and photoluminescent spectra for the crystal powder samples and the aqueous solutions of 1 and 2 have been investigated. The DFT and TDDFT calculations at B3LYP/6–31G* level for 1 and B3LYP/Lanl2dz level for 2 have been used to demonstrate the characteristic absorption spectra and the trans ‐enol to cis ‐keto photo‐ and thermoisomeric reaction for the ATSA 3− anion. The onion cell imaging taken by confocal laser scanning microscope was observed with 1 and 2 as fluorescent labels.