Trinuclear copper (I) pyrazolate complexes for vapochromic sensing of aromatic volatile organic compounds

Abstract

Vapochromism using optical chemosensors of d10 group metal complexes have a great potential for sensing different kinds of volatile organic compounds (VOCs) by vapor-triggered color and luminescence changes. Since organic aromatic vapors are mainly hazardous and carcinogenic to human health and environment, it is interesting challenge to develop the low-cost vapochromic chemosensors with high sensing capability. On the other hands, inorganic complexes and materials have been found to change their color and luminescence properties by modifying molecular structures. However, there is no study on, the relationship of molecular structures for chemosensors of VOCs such as aromatic vapors. Therefore, we report systematic study on by using supramolecular assembly of a weak metal-metal interaction, optical response of trinuclear copper(I) pyrazolate complexes ([Cu3Pz3]) for vapochromic chemosensors of benzene, toluene and hexafluorobenzene. The [Cu3Pz3] complexes have been successfully synthesized from 3,5-dimethyl (complex A), 3,5-trifluoromethyl (complex B), 3,5-diphenyl (complex C) and 4-(3,5-dimethoxybenzyl)-3,5-dimethyl (complex D) pyrazole ligands as a solid powder. The resulting complexes showed color emission in the range from red to green upon exposure to a UV hand lamp (254 nm) in dark room, which were in good agreement with emission spectra upon excitation at 280 nm; 590 nm (complex A), 570 nm (complex B), 614 nm (complex D) and upon excitation at 321 nm for emission at 642 nm (complex C). The sensing capability of all [Cu3Pz3] complexes with different molecular side-chains showed different phenomena depending on the types of aromatic solvents. In contrast to no response of complex A upon exposure to VOCs, complexes B and C showed gradually quenching of the intensity due to cleavage of Cu(I)-Cu(I) interaction. Interestingly, complex D showed blue shifting of its emission center due to enhancement of the metal-metal distance.