Synthesis of group 11 pyrazolate complexes bearing different alkyl side-chains for vapochromic chemosensors of volatile organic compounds

Abstract

Vapochromic chemosensors of phosphorescent metal complexes have been developed previously for the detection of volatile organic compounds (VOCs) without studying the effect of molecular structure on their sensing capabilities. Therefore, this research aims to synthesize phosphorescent trinuclear Group 11 pyrazolate complexes in a variety of molecular structures, based on amphiphilicity of different alkyl side-chains of the pyrazolate ligands and type of metal ions for development of new optical chemosensors for the VOCs detection. Trinuclear pyrazolate complexes (3d1–3d7) were synthesized by complexation of copper(I) with non-side chain, 3,5-dimethyl, 3,5-bis(trifluoromethyl), 3,5-diphenyl, 4-(3,5- dimethoxybenzyl)-3,5-dimethyl, 4-(3,4,5-trioctadecoxybenzyl)-3,5-dimethyl and 4- (3,4,5-tridecoxy triethylene glycol benzyl)-3,5-dimethyl pyrazole ligands (3c1–3c7), including 3c5 and 3c7 ligands with gold(I) and silver(I) to give 3e5, 3e7 (silver(I)) and 3f5, 3f7 (gold(I)) complexes. All the complexes showed emission bands in the range 553-644 nm when excited at 275-322 nm with large Stokes shifts (>300 nm) and luminescent lifetimes in the microscale. Moreover, they emitted from green to red when exposed to UV light at 254 nm, exhibiting phosphorescent properties from the weak metal-metal interactions. Upon exposure to alcohol derivatives, 3d5 performed the best for detection of ethanol and caused a blue-shift of the emission spectra, while amphiphilic 3d7 was found to be the best chemosensor as demonstrated by quenching of the emission intensity in the presence of hexanol. When exposed to benzene, amphiphilic 3e7 showed the best sensing capability for the detection of benzene and its derivatives, which is an important new finding emerging from this study. Therefore, phosphorescent chemosensors with high sensing capabilities could be achieved by controlling the molecular structure and fine-tuning of the amphiphilicity of the different alkyl side-chains of the pyrazolate ligands in the presence of different types of metal ions for the detection of specific VOCs.