Spectral investigation of phthalocyanine complexes of high-valence silver and their aggregates

Syntheses of Water-Soluble Silver(II)–Phthalocyanines toward Optical Sensing for Thiol Detection

“…The appearance of the dimer band only at the blue flank of the monomer band but not at the red flank is indicative of the formation of cofacial dimers according to Kasha’s exciton coupling theory . This has been further supported by the appearance of a sigmoid curve with its center at the peak wavelength in the MCD spectrum of [Ag­(tEtpySpc)] at a higher concentration (i.e., Faraday A -term; Figure ) because the dimer Q-band must be also doubly degenerate in cofacial dimers. ,,,, The methyl-substituted analog behaves essentially in the same manner (Figure S2). It seems that the disaggregation-promoting performance of polyethyleneglycol ethers (PEG) depends on the length of the PEG chain and their performance is in the following order; PEG50 > > PEG20 > PEG10.…”

“…Water-soluble AgPcs can be a potent biothiol sensor because of the rapidness, high sensitivity, and selectivity against thiols as well as the bold contrast between before and after the reaction. Earlier studies on AgPcs have reported that reduction of AgPcs gave rise to expulsion of silver ions from the cavity of the macrocyclic ligand. , Lever and co-workers have rationalized the change in lability of the central metal ion upon the reduction with the increase in the ionic radius (126 nm for silver­(I) while 89 pm for silver­(II)) . There have been similar discussions for porphyrin analogs. , Therefore, the reaction of AgPcs with thiols may involve electron transfer from thiols to silver­(II).…”

“…Both the two AgPcs are moderately soluble in polar solvents, such as pyridine (slightly), acetonitrile, nitrobenzene (moderately), nitromethane, DMA, DMSO, and water (although strongly aggregated therein) while insoluble in common organic solvents, such as toluene, hexane, acetone, ethanol, dichloromethane, and chloroform. The use of more common quarternizing reagents like alkyl iodide was unsuccessful as expected because iodide as the byproduct should reduce the silver­(II) to silver­(I) and finally result in demetallation . For example, the use of methyl iodide in place of trimethyloxonium tetrafluoroborate yielded metal-free tetrakis­{4-( N -methyl pyridinium)­thio}­phthalocyanine as the main product.…”

“…Quite recently, we have reported silver­(II)–Pc complexes (AgPcs) . While silver ions are generally considered the most stable in the +1 oxidation state, their higher oxidation states (+2/+3) are stabilized in multidentate N-donor ligands, such as porphyrins, corroles, and cyclam − and in Pcs. − The potential oxidizing power and high affinity against sulfur of the central metal ion can make AgPcs excellent chemical probes for the above-mentioned biothiols.…”

“…This speculation inspired us to study if AgPcs can react with deprotonated sulfhydryl groups in aqueous solutions. Furthermore, the reduction of essentially nonfluorescent AgPcs (due to the paramagnetism of silver­(II)) causes rapid demetallation and generates a corresponding more fluorescent metal-free macrocyclic ligand . This work has been undertaken to investigate if water-soluble AgPcs can react with amino acids containing sulfhydryl groups in aqueous media and work as optical sensors for biothiols.…”