Solvent effects on molecular aggregation of highly water-soluble phthalocyanines

Abstract

Molecular aggregation phenomena of a highly water-soluble, metal-free phthalocyanine, H 2 Pc, and its copper complex, Cu(Pc); where Pc denotes tetrakis{(2′,6′-dimethyl-4′-sulfonic acid) phenoxy}phthalocyaninate) in water, ethanol, and their mixed solvent systems have been investigated by spectroscopic approach. In both aqueous and ethanolic solutions, H 2 Pc molecules aggregate in a slipped-cofacial manner, although very weakly in ethanol. On the other hand, Cu(Pc) molecules aggregate in a cofacial manner in water while aligning in a slipped-cofacial manner in ethanol. Magnetic circular dichroism spectroscopy was undertaken to investigate aggregation behaviors of Cu(Pc) in water and ethanol. Presence of 4-phenylpyridine in ethanol effectively inhibited aggregation of Cu(Pc) molecules, although little affected the spectra of the monomers. In a mixed solvent system, where water/ethanol = 10/90 (v/v), Cu(Pc) is free from aggregation up to almost 10 -4 M. Driving forces of this molecular aggregation are discussed on the basis of p-p interaction and coordination chemistry involving copper ions. KEYWORDS:water-soluble, phthalocyanine, copper, metal-free, magnetic circular dichroism, aggregation-disaggregation, J-aggregation, solvent effects.

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

“…For example, Figure a,b exhibits typical optical absorption and emission spectral changes observed for an aqueous [Ag­(tEtpySpc)] solution containing PEG50 (as a surfactant) and Cys. The absorption spectra without thiols are assignable to a mixture of AgPc monomer and dimer as described above, while those of the reaction products show two absorption bands with almost the same intensity in the Q-band region and hence are characteristic of metal-free Pcs. − Moreover, the excitation spectra (the blue dashed lines in Figure b) corresponding to the optical emission of the reaction products are very close to absorption spectra of metal-free Pcs, confirming the absence of silver ions within the fluorophore. Figure c shows photographs of an aqueous solution containing [Ag­(tEtpySpc)] and PEG50 under irradiation of a blacklight (365 nm) before and after the addition of Cys to the solution.…”

“…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.…”

“…On the other hand, both the absorption spectra of [Ag­(tEtpySpc)] and [Ag­(tMepySpc)] show a broad absorption band around the Q-band envelope (Figure ). The spectra are typical of strongly aggregated Pcs in aqueous solutions. ,,− From the viewpoint of application of Pcs as a fluorescent chemical probe, molecular aggregation phenomena are quite unfavorable first because aggregated molecules can be deactivated due to steric hindrance and second because aggregated Pc molecules are much less fluorescent than monomers , even though they can react with the desired substrates in aggregated forms. Therefore, the effects of aggregation need to be minimized.…”

“…Therefore, the effects of aggregation need to be minimized. In general, some common surfactants, such as sodium dodecyl sulfate (SDS), sodium dodecyl sulfonate, methyl trioctylammonium chloride, Triton X-100, and Tween 20, are capable of disaggregating Pcs in water. ,− Nevertheless, apart from SDS, they contribute little or only insufficiently to disaggregation of AgPc molecules in water. SDS exhibits excellent disaggregating performance (Figure ): with an increase in SDS concentration, the spectra around the Q-band envelope turned better isolated and, at [SDS] = ca.…”

Alcian blue pyridine variant interaction with DNA and RNA polynucleotides and G-quadruplexes: changes in the binding features for different biosubstrates

“…Given the known strong tendency of phthalocyanines to undergo auto-aggregation phenomena [6,[29][30][31], this feature was re-checked here for ABTP under our experimental conditions. In water, absorbance profiles do not seem to change with dye concentration and absorbance vs. concentration plots are linear (Figure S1A-B of the Supporting Information).…”