Supramolecular assembly of group 11 phosphorescent metal complexes for chemosensors of alcohol derivatives

Abstract

Abstract. We report on systematic study on vapochromic sensing of ethanol by using phosphorescent trinuclear metal pyrazolate complexes with supramolecular assembly of weak intermolecular metal-metal interactions using 4-(3,5-dimethoxybenzyl)-3,5-dimethyl pyrazole ligand (1) and group 11 metal ions (Cu(I), Ag(I), Au(I)). Upon excitation at 284, the resulting complexes showed emission bands with a peak centered at 616, 473 and 612 nm for 2(Cu), 2(Ag) and 2(Au), respectively. Chemosensor 2(Cu) showed positive response to ethanol vapors in 5 mins by blue-shifting its emission band from 616 to 555 nm and emitting bright orange to green. Otherwise, 2(Au) gave shifting from its emission band centered at 612 to 587 nm with Δλ of 25 nm (41%) and color changes from red-orange to light green-orange while 2(Ag) showed quenching in its original emission intensity at 473 nm in 40% with color changes from dark green to less emissive. These results demonstrate that sensing capability of chemosensor 2(Cu) with suitable molecular design of ligand and metal ion in the complex is due to the formation of a weak intermolecular hydrogen bonding interaction of O atom at the methoxy of the benzyl ring with the OH of the vapors at the outside of the molecules.

Systematic Study on Sensing Capability of Gold(I) Pyrazolate Complex for Vapochromic Chemosensors of Ethanol Vapors

“…The structure of a trinuclear gold(I) pyrazolate complex was elucidated using a mass spectrometer and FT-IR spectroscopy. The mass spectrum of this gold(I) complex was previously reported using LC-TOF-MS where the complex showed similar monoisotopic pattern at mass per charge (m/z) of 1326.29 Dalton originated from the trimer structure of Au3C42H51N6O6 [29,30]. Further analysis was performed using FT-IR spectroscopy as shown in Figure 3 where N-H stretching vibration at a wavenumber of 3075-3171 cm -1 for the pyrazole ligand (red line) is visible.…”

“…Further analysis was performed using FT-IR spectroscopy as shown in Figure 3 where N-H stretching vibration at a wavenumber of 3075-3171 cm -1 for the pyrazole ligand (red line) is visible. The disappearance of this vibration band in the pyrazolate complex (black line) is due to the formation of the bonding between Au and N atoms in the pyrazole ring [29,30]. Meanwhile, the other existing vibration bands were left unchanged in the spectrum of both the ligand and complex.…”

“…The sample was placed on top of the crystal in ATR for the monitoring of the FT-IR spectrum. Previously, another structure elucidation was reported by using a time-of-flight mass spectrometer with an interface of liquid chromatography (LC-TOF-MS) [30]. Optical properties were recorded using JASCO UV-visible spectrometer on a model of V-760 for the absorption spectrum and JASCO FP-8500 ST spectrofluorometer for the emission spectrum.…”

“…The sensing capability of the chemosensor was evaluated using the same spectrofluorometer for monitoring changes in emission properties. Figure 1 shows the synthetic route for the preparation of gold(I) pyrazolate complex from pyrazole ligand as previously reported [29,30]. Typically, the as-synthesized 4-(3,5-dimethoxybenzyl)-3,5-dimethyl pyrazole ligand (4.06 mmol, 1.00 g) in 50 mL of dry tetrahydrofuran (THF) was firstly mixed with 4.06 mmol (1.19 g) of chloro(dimethyl sulfide)gold(I) ([Au(SMe2)]Cl) in a Schlenk under an inert condition.…”

“…Recently, we have reported that trinuclear phosphorescent gold(I) 4-(3,5dimethoxybenzyl)-3,5-dimethyl pyrazolate complex was successfully utilized for sensing benzene in 5 minutes where its emission intensity was quenched up to 81% and can be autonomously recovered without external stimuli [29]. In contrast to this performance, gold(I) 4-(3,5-dimethoxybenzyl)-3,5dimethyl pyrazolate showed a small shift away from its emission intensity to the blue region upon 5 minutes exposure to EtOH [30]. Considering the properties of gold(I) 4-(3,5-dimethoxybenzyl)-3,5dimethyl pyrazolate and its two different interactions toward benzene and EtOH as previously accounted for, we herein report the sensing capability of this chemosensor by systematically investigating its performance under EtOH exposure.…”