Mopelola Idowu

Generation of singlet oxygen via the composites of water-soluble thiol-capped CdTe quantum dots-sulfonated aluminum phthalocyanines.

Singlet oxygen (1O2), one of the reactive oxygen species, plays an important role in many biomedical applications. The various compounds including the phthalocyanines, quantum dots (QDs) and QD complex, which may have potential to produce 1O2, thus received more and more attentions in recent years. By means of the direct detection of near-infrared 1270 nm, we found that the water-soluble thiol-capped CdTe QDs can photoproduce 1O2 in deuterated water with a low quantum yield (QY) of 1%. When sulfonated aluminum phthalocyanines (AlSPcs) were connected to these QDs, forming water-soluble QD-Pc composites, the 1O2 QY of the composites increased to 15% under the excitation of 532 nm, while little 1O2 production can be found for AlSPc alone at the same excitation because of the poor absorption of AlSPc in this region. The results of indirect measurements of 1O2, obtained from the photodegradation of the 1O2 chemical trap anthracene-9,10-diyl-bis-methylmalonate (ADMA), confirmed 1O2 yields in both QD and QD-Pc composite solutions. The QD-Pc composites have the advantage of extending the excitation region to 400-600 nm with remarkably enhanced extinction coefficients as compared with that of AlSPc. Therefore QD-Pc composites can fully utilize visible region light excitation to effectively produce 1O2, which may facilitate the applications of QD-Pc composites in broad areas.

Photoinduced energy transfer between water-soluble CdTe quantum dots and aluminium tetrasulfonated phthalocyanine

Thiol stabilized CdTe quantum dots (QDs) synthesized in aqueous phase were used as energy donors to aluminium tetrasulfonated phthalocyanine (AlTSPc) through fluorescence resonance energy transfer (FRET). Energy transfer occurred from the QDs to AlTSPc upon photoexcitation of the QDs. An enhancement in efficiency of energy transfer with the nature of the carboxylic thiol stabilizers on the QDs was observed. The results showed that for enhanced FRET to occur, the donor–acceptor distance has to be lower than the critical distance. The quenching constant K as well as the binding constant kb values were calculated suggesting strong interaction of the QDs with the AlTSPc. Study of the photophysics of AlTSPc in the presence of the QDs revealed a high triplet state yield, hence the possibility of using QDs in combination with phthalocyanines as photosensitizers in photodynamic therapy. The triplet state lifetimes of AlTSPc in the presence of the QDs were calculated and the lifetime in the presence of CdTe capped with 3-mercaptopropionic acid (MPA) was found to be the longest. MPA capped QD in a mixture with AlTSPc resulted in long triplet lifetime and high triplet yield of the latter, and high energy transfer efficiency, hence was found to be most suitable as a potential candidate for photodynamic therapy of cancer studies.

Photoelectrochemical characterization of electrodeposited ZnO thin films sensitized by octacarboxymetallophthalocyanine derivatives

Hybrid thin films of crystalline zinc oxide (ZnO) modified by different octacarboxymetallophthalocyanines (MOCPc) were prepared by the readsorption method. Homogeneously blue or green thin films were formed. The photoelectrochemical characteristics of the electrodes were studied by time-resolved photocurrent measurements. Zinc(II) 2,3,9,10,16,17,23,24-octacarboxyphthalocyanine (ZnOCPc) showed considerably large quantum efficiency in sensitization of ZnO, one of the highest quantum efficiencies obtained so far with phthalocyanine-type sensitizers on nanocrystalline ZnO films.

Protonation of some non-transition metal phthalocyanines — spectral and photophysicochemical consequences

The photophysics and photochemistry of phthalocyanine complexes of magnesium (MgPc), aluminum chloride (ClAlPc) and zinc (ZnPc) are studied in N,N′-dimethylformamide (DMF). The values obtained for the photophysical and photochemical parameters are normal for simple metallophthalocyanine (MPc) complexes. Protonation of the azomethine bridges reduced the photoactivities of the complexes considerably; however the excited triplet states of the protonated species are more stable towards ground state oxygen. The interaction of the non-protonated MPcs with ground state oxygen is shown to be diffusion-assisted, with bimolecular rate constant values of the order of 1010 M-1.s-1. MgPc could not be protonated; it was easily demetalated by the protonating acid. The kinetics of the demetalation yielded the rate equation: Rate = 0.1[MgPc][H+]2/3

Spectroscopic behavior of cationic metallophthalocyanines in the presence of anionic quantum dots.

The interactions and spectroscopic properties between cationic zinc phthalocyanine derivatives (peripherally and non-peripherally tetrasubstituted and peripherally octa substituted with 2-diethylmethylaminoethylsulfanyl (betaTZnPc, alphaTZnPc and betaOZnPc)) and CdTe core quantum dots (QDs) capped with mercaptopropionic acid or thioglycolic acid (represented as CdTe@MPA and CdTe@TGA, respectively) have been studied in methanol:water mixture. Strong coupling of MPcs was deduced from the interaction since the UV-vis spectroscopic studies of the ground state complex formed on mixing both components showed loss of the phthalocyanine monomeric band with the formation of a dimeric band (spectrum of aggregated species). The dimerization constants were of the order of 10(4)M(-1).

Synthesis and photophysical properties of peripherally and non-peripherally mercaptopyridine substituted metal free, Mg(II) and Al(III) phthalocyanines

The syntheses and photophysical properties of metallophthalocyanines containing Mg(2+) and Al(3+) as central metal ions and their unmetallated derivative (complexes 3-8) tetra- substituted at the non-peripheral (α) and peripheral (β) positions with 2-mercaptopyridine are reported. The trends in triplet and fluorescence quantum yields are described for these compounds. The complexes exhibited relatively high triplet quantum yields (Φ(T)) ranging from 0.33 to 0.54 and fluorescence quantum yields (Φ(F)) ranging from 0.02 to 0.29. Triplet state lifetimes of the complexes were long ranging from 120 to 460 μs, indicating a potential use of these complexes as photosensitizers.

Photophysicochemical behavior and antimicrobial activity of dihydroxosilicon tris(diaquaplatinum)octacarboxyphthalocyanine.

Platination of dihydroxosilicon octacarboxyphthalocyanine (OH)2SiOCPc was successfully carried out to give dihydroxosilicon tris(diaquaplatinum)octacarboxyphthalocyanine (OH)2SiOCPc(Pt)3 conjugate. Slight blue shifting of the absorption spectrum of (OH)2SiOCPc(Pt)3 was observed on conjugation with platinum. Comparative photophysicochemical behavior and antimicrobial photo-activities of (OH)2SiOCPc(Pt)3 conjugate with (OH)2SiOCPc or Pt nanoparticles revealed that the heavy atom, Pt on the periphery of the phthalocyanine significantly enhanced its singlet oxygen generation with a quantum yield of 0.56 obtained for the (OH)2SiOCPc(Pt)3 conjugate. The (OH)2SiOCPc(Pt)3 conjugate showed highest antimicrobial activity towards Candida albicans and Escherichia coli compared to (OH)2SiOCPc and Pt nanoparticles alone under illumination.

Spectral properties and photophysical behaviour of water soluble cationic Mg(II) and Al(III) phthalocyanines

AbstractPeripherally and non-peripherally tetrasubstituted-[(N-methyl-2-pyridylthio)]phthalocyaninato magnesium (II) (5 and 6) and chloro aluminium (III) (7 and 8) tetraiodide have been synthesized and characterized. The photophysical properties of the complexes in dimethyl sulfoxide (DMSO) and aqueous medium in the presence and absence of cremophore EL have been studied. These complexes show high solubility in aqueous medium though they were aggregated. The triplet state quantum yields (FT) and the triplet lifetimes (tT) were found to be higher in DMSO with ΦT ranging from 0.32 to 0.51, while tT ranged from 282 to 622 ms in DMSO, compared to aqueous medium (pH 7.4 buffer) where ΦT ranged from 0.15 to 0.19 and tT from 26 to 35 ms. Addition of cremophore EL in aqueous solution resulted in partial disaggregation and increased photoactivity. The fluorescence lifetimes of the complexes showed strong dependence on their immediate environment. The ionic magnesium(II) and aluminium(III) phthalocyanines strongly bind to bovine serum albumin (BSA).

Photophysicochemical behaviour and antimicrobial properties of monocarboxy Mg (II) and Al (III) phthalocyanine-magnetite conjugates

Asymmetric Mg (II) or Al (III) phthalocyanine (containing a COOH group and 3-pyridylsulfanyl units) was conjugated via an amide bond to amino functionalized magnetic nanoparticle (AIMN) to form MgPc-AIMN or AlPc-AIMN conjugate, and characterized. The photophysicochemical behaviour of the phthalocyanine-AIMN conjugates was investigated and compared to the asymmetric Pcs and to the simple mixture of Pc with AIMNs without a chemical bond, (MPc-AIMN (mixed)). The directed covalent linkage of AIMNs to the asymmetrical metallopthalocyanines afforded improvements in the singlet oxygen (ФΔ) and triplet state quantum yield (ФT) as well as singlet oxygen lifetimes for the MPcs-AIMN-linked conjugates compared to MPc-AIMN (mixed) and MPcs alone. The asymmetric phthalocyanines and their conjugates showed effective antimicrobial activity against Escherichia coli bacteria under illumination.