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The coordination system of rare-earth n-tuple decker phthalocyanines would be better suited with appropriate metal ions with the correct coordination number and the solvent system of the reaction, amongst other reasons, for the formation of n-tuple decker phthalocyanines. As a result, these complexes are very rare. In this manuscript, we present new n-tuple decker phthalocyanines in the form of double- (complex 2), quadruple- (complex 3a) and sextuple-decker phthalocyanines (complex 3b), all of which contain neodymium and cadmium metal ions. The primary focus is the investigation of the nonlinear optical (NLO) mechanisms responsible for the observed reverse saturable absorption. While the extension of the π-electron system has been found to enhance the nonlinear optical behavior of complexes 3a and 3b, a change in the NLO mechanisms has been observed, with complex 2 lacking the triplet state population, as revealed by a laser flash photolysis technique. It has also been established that the excited state absorption cross sections follow a clear order of magnitude for the complexes under investigation: σ23 (for 3b) > σ23 (for 3a) > σ1m (for 2). This trend evidences the effects of the extension of the π-electron system.

This manuscript presents the non-linear optical parameters obtained specifically at 532 nm using the new bis-{1(4),8(11),15(18),22(25)-(tetrapyridin-3-yloxy) phthalocyaninato} neodymium(III) complex in green (2a) and blue (2b) forms as well thin films prepared from the green form in the presence of poly(bisphenol A) carbonate. It is interesting to note a huge improvement of the reduction efficiency of transmission of the green form by 34% in poly(bisphenol A) carbonate as a thin film. The same observation is noted for the blue form at 25%. The same trend was observed for the excited state cross sections in which the blue form of the bis-{1(4),8(11),15(18),22(25)- (tetrapyridin-3-yloxy) phthalocyaninato} neodymium(III) complex as well as the thin film exhibited values that were about three and six times greater than those of the green form, respectively. The electrochemical properties were also studied, with complex 2a exhibiting six redox processes in DCM, by employing tetrabutylammonium tetrafluoroborate as an electrolyte.

Unsubstituted zinc phthalocyanine (ZnPc), 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]-phthalocyanine (ZnTPPcQ) and Zn tetrasulfo phthalocyanine (ZnTSPc) were non-covalently (electrostatic and/or π–π interaction) attached to graphene quantum dots (GQDs) to form GQDs-Pc nanoconjugates. Relative to Pcs alone, the presence of GQDs improved the triplet quantum yields with the following values: GQDs-ZnPc (0.73), GQDs-ZnTPPcQ (0.76) and GQDs-ZnTSPc (0.67). Respective Förster resonance energy transfer (FRET) efficiencies were calculated to be 0.81, 0.80 and 0.28. However, singlet oxygen generating abilities of the as-synthesized nanoconjugates were relatively low due to the screening effect of GQDs and quenching in water. This study shows that, the type of Pc, loading and solvent used are among the vital properties to consider when constructing GQD-nanoconjugate systems with optimal triplet quantum yield properties and investigation of their physicochemical properties.

Asymmetric mono-carboxy-porphyrins, (5-(4-carboxyphenyl)−10,15,20-tris(pentafluorophenyl)porphyrinato zinc(II) (1), 5-(4-carboxyphenyl)−10,15,20-triphenylporphyrinato zinc(II) (2) and 5-(4-carboxyphenyl)−10,15,20-tris(2-thienyl)porphyrinato zinc(II) (3), were linked to Ag nanoparticles (AgNPs) through amide bonds and self-assembly (the latter only for 3). The porphyrins and conjugates were used for photodynamic antimicrobial chemotherapy (PACT) against Staphylococcus aureus. PACT uses singlet oxygen for antimicrobial activity. Complex 3 and its conjugates had higher singlet oxygen quantum yields and higher log reduction when compared with the rest of the porphyrins and corresponding conjugates. These high log reductions for 3 and its conjugate were attributed to the presence of sulfur groups whereby there was more interaction with the bacterial membrane.

This manuscript reports on syntheses of new multi-decker phthalocyanines, namely: bis-{2,3,9,10,16,10,16,17,23,24-octa(4-tertbutylphenoxy) phthalocyaninato} cerium(III) (2), tris-{2,3,9,10,16,10,16,17,23,24-octa(4-tertbutylphenoxy) phthalocyaninato} dicerium(III) (4) and bis-{2,3,9,10,16,10,16,17,23,24-octa(4-tertbutylphenoxy) phthalocyaninato} gadolinium(III) (5). Complex 4 which is a tris phthalocyanine showed better nonlinear optical behavior in solution than 2 which is a bis phthalocyanine, both containing the same central metal, Ce. All the three molecules possess good optical limiting properties judged by the limiting threshold values which ranged from 0.04 to 0.09 J cm−2 with complex 5 embedded in thin films, showing the lowest value of 0.04 J cm−2. Furthermore, nonlinear optical processes responsible for reverse saturable absorption data are investigated.

Bis{1(4), 8(11), 15(18), 22(25)-tetra(4- tert -butylphenoxy)phthalocyaninato} ytterbium(III) ( 2a ) (the green form) was synthesized and reduced to form 2b (the blue form). Nonlinear optical parameters for complex 2 in green and blue forms were determined using the Z-scan technique and the values of third-order imaginary susceptibility (Im[ χ (3) ]) and second-order hyperpolarizability ( γ ) of the order of 10 −9 (for 2b ) and 10 −27 esu, respectively, were obtained in solution. In poly(acrylic acid) as a thin film, complex 2a showed extremely high Im[ χ (3) ] and γ values of the order 10 −8 and 10 −25 respectively. A low optical limiting threshold value of 0.075 J cm −2 was obtained for the thin film 2a .

In this article, we report on the linking of cobalt tetrakis (4-pentyn-oxy) phthalocyanine (CoTPPc) to ZnO nanoparticles via click chemistry. Subsequently, electrocatalytic activity and nonlinear optical properties were investigated (the latter using an open Z-scan technique at 532 nm). The linking of CoTPPc with ZnO resulted in the lowest limiting intensity value of 0.27 J.Cm−2, the β eff (cmW−1) values were found to be 1.51 × 10-8 and 7.10 × 104 for ZnO and CoTPPc-ZnO respectively. The catalytic rate constants (M−1s−1) (and limits of detection) were 4.1 × 104 (12.87 µM), 5.7 × 104 (8.62 µM) and 7.36 × 104 (4.35 µM) for ZnO, CoTPPc and CoTPPc-ZnO. Hence linking ZnO nanoparticles to CoTPPc result in the enhancement of both nonlinear optical behaviour and catalytic activity.

Syntheses of bis{23-(3,4-di-yloxybenzoic acid)-(2(3), 9(10), 16(17), 23(24))-(hexakis-pyridin-3-yloxy phthalocyaninato)} dineodymium (III) acetate ( 3 ) and 2(3), 9(10), 16(17), 23(24)-(tetrapyridin-3-yloxy phthalocyaninato) neodymium (III) acetate ( 4 ) as well as their conjugates with ZnO nanoparticles (conjugates 6 , 7 and 8 ) are presented. Thin films of conjugate 6 (where complex 3 is linked to ZnO nanoparticles via an amide bond) gave the best third-order susceptibility (5.89 × 10 −8 esu), second-order hyperpolarizability (2.53 × 10 −25 esu) and the lowest limiting threshold values (0.12 J cm −2 ). The nonlinear behavior is enhanced in solid state when compared to solution.

The optical behavior of bis-{2(3), 9(10), 16(17), 23(24)-(tetrapyridin-4-yloxy phthalocyaninato)} lanthanum (III) (2) and its ytterbium (3) counterpart in dimethyl sulfoxide are presented and compared to bis-{1(4), 8(11), 15(18), 22(25)-(tetrapyridin-4-yloxy phthalocyaninato)} ytterbium (III) (4). We report on the third-order susceptibility, second-order hyperpolarizability and the limiting threshold values. The nonlinear optical limiting threshold values of complexes 2, 3 and 4 showed improvement in the solid state (thin films), with complex 4 giving the best value at 0.033 J cm−2.

Tris-{1(4),8(11),15(18),22(25)-tetra(4-tertbutylphenoxy) phthalocyaninato} dineodymium (III) was synthesised and its nonlinear optical and fluorescence behavior was studied. Low fluorescence quantum yield ( Ф F = 0.03) was obtained with a fluorescence lifetime τ F = 4.31 ns for this complex. Nonlinear optical parameters for the complex were determined using the Z-scan technique and the values of Im[ χ (3) ] and γ were of the order of 10 −10 and 10 −28 esu, respectively. Square wave voltammetry revealed three reduction and two oxidation couples for the complex.

2,4,6-Tris[3-thio-9,10,16,17,23,24-hexa(4-tertbutylphenoxy) phthalocyaninato ytterbium (III) chloride]-s-triazin ( 3 ) and its lutetium counterpart ( 4 ) were synthesized. The nonlinear optical behavior of 3 and 4 were characterized in solution and when embedded in polymer as thin films. Thin films of complexes 3 and 4 in poly(bisphenol A carbonate) showed improved nonlinear optical properties when compared to solution. Complex 3 showed a lower threshold for optical limiting intensity ( I lim ) than complex 4 , and for phthalocyanines in general. I lim values were even lower in films compared to solutions.

We report original, selective, and efficient approaches to novel nonlinear optical (NLO) materials, namely homoleptic double- and triple-decker europium(III) complexes 2 and 3 with the A3 B-type phthalocyanine ligand (2,3-bis[2'-(2''-hydroxyethoxy)ethoxy]-9,10,16,17,23,24-hexa-n-butoxyphthalocyanine 1) bearing two anchoring diethyleneglycol chains terminated with OH groups. Their covalently linked nanoconjugates with mercaptosuccinic acid-capped ternary CdSeTe/CdTeS/ZnSeS quantum dots are prepared in the presence of an ethyl(dimethylaminopropyl)carbodiimide activating agent. Optical limiting (OL) properties of the obtained low-symmetry complexes and their conjugates with quantum dots (QDs) are measured for the first time by the open-aperture Z-scan technique (532 nm laser and pulse rate of 10 ns). For comparison, symmetrical double- and triple-decker EuIII octa-n-butoxyphthalocyaninates 5 and 6 and their mixtures with trioctylphosphine oxide-capped QDs are also synthesized and studied. It is revealed that both lowering of molecular symmetry and expansion of the π-electron system upon moving from double- to triple-decker complexes significantly improves the OL characteristics, making the low-symmetry triple-decker complex 3 the most efficient optical limiter in the studied family of sandwich complexes, affording 50 % lowering of light transmittance below 0.5 J cm-2 input fluence. Conjugation (both covalent and noncovalent) with QDs affords further enhancement of the OL properties of both double- and triple-decker complexes. Altogether, the obtained results contribute to the development of novel nonlinear optical materials for future nanoelectronic and optical device applications.

Herein we report on the syntheses, photophysico-chemical properties and nonlinear absorption parameters of bis-{1(4), 8(11), 15(18), 22(25)-(tetrapyridin-2-yloxy phthalocyaninato)} ytterbium (III) (3) and bis-{1(4), 8(11), 15(18), 22(25)-(tetrapyridin-4-yloxy phthalocyaninato)} ytterbium (III) (4). The fluorescence and singlet oxygen quantum yields obtained for complexes 3 and 4 are low. The triplet quantum yield obtained for complex 3 is high at ΦT = 0.89 whereas for complex 4 ΦT = 0.48. The third order optical susceptibility values are of the order: 10−11 esu (for complex 3), and 10−13 esu (for complex 4) while the hyperpolarizability values are of the order: 10−28 esu (for complex 3) and 10−31 esu (for complex 4). Complexes 3 and 4 show two-photon absorption coefficients of the order of 10−46 cm4 s/photon and 10−48 cm4 s/photon, and threshold intensities as low as 0.3 J cm−2 and 0.0045 J cm−2, respectively.

The synthesis, photophysicochemical properties and photodynamic activity (PDT) of 4(4-phenyldiazenyl) phenoxy substituted indium (III) (InPc) and zinc (ZnPc) phthalocyanines when alone or incorporated into Pluronic® F127 micelles are presented in this study. The InPc exhibited higher singlet oxygen (ΦΔ) at 0.47 compared to the ZnPc at 0.20 in dimethylsulfoxide. The ΦΔ values in the presence of Pluronic® F127 and in water, were 0.32 for InPc and 0.09 for ZnPc. The triplet quantum yields (ΦT) were 0.92 for InPc and 0.32 for ZnPc in DMSO. The PDT activity followed the same trend as the singlet oxygen quantum yields. At the highest concentration, InPc in Pluronic® F127 gave 22% cell viability compared to 34% for complex ZnPc. The partition coefficient Kp values were determined using the water and octanol system. InPc had a larger Kp suggesting that it is more likely to be taken up by the cancer cells, hence it exhibited better PDT activity.

Core–shell CdTe@ZnS quantum dots capped with glutathione (CdTe@ZnS–GSH) were covalently linked to zinc octacarboxy phthalocyanine (ZnPc(COOH) 8 ). The conjugate was characterized by UV/Vis, infrared and X-Ray photoelectron spectroscopies as well as transmission electron and atomic force microscopies. The fluorescence quantum yields of the core CdTe capped with thioglycolic acid increased upon formation of the core-shell. Upon conjugation with ZnPc(COOH) 8 , the fluorescence quantum yield of CdTe@ZnS–GSH decreased due to energy transfer from the latter to the Pc. The average fluorescence lifetime of the CdTe@ZnS–GSH QD also decreased upon conjugation from 26.2 to 13.3 ns.

Conjugates of zinc tetracarboxy phthalocyanine (ZnPc(COOH)4) with CdTe@ZnS–GSH quantum dots (QDs) were synthesized and characterized by several techniques including X-ray powder diffraction and infrared spectroscopy. There was an observed decrease in both the fluorescence quantum yields and lifetimes of the quantum dots when they were linked or mixed with ZnPc(COOH)4 due to Forster resonance energy transfer (FRET). The FRET behavior of CdTe@ZnS–GSH–ZnPc(COOH)4 conjugates was compared to that of CdTe@ZnS–GSH–ZnPc(COOH)8. Higher FRET efficiencies were observed for CdTe@ZnS–GSH–ZnPc(COOH)4-mixed or CdTe@ZnS–GSH–ZnPc(COOH)4-linked compared to the corresponding CdTe@ZnS–GSH–ZnPc(COOH)8-mixed or CdTe@ZnS–GSH–ZnPc(COOH)8-linked. Also CdTe@ZnS–GSH–ZnPc(COOH)4-mixed (containing coreshell QDs) showed higher FRET efficiency than CdTE–TGA–ZnPc(COOH)4-mixed containing core QDs. The FRET efficiencies were found to be 63% and 59% for the CdTe@ZnS–GSH–ZnPc(COOH)4-linked and CdTe@ZnS–GSH–ZnPc(COOH)4-mixed samples, respectively.

A rare earth sandwich-type phthalocyanine: bis-{2,3,9,10,16,17,23,24-octa(4-tert-butylphenoxy) phthalocyaninato} lutetium(III) has been synthesized. The photophysical and nonlinear optical behavior of both the “green” and “blue” forms ([LuIIIPc2] and [LuIIIPc2]−, respectively) of the complex have been investigated. High triplet state and singlet oxygen quantum yield values were obtained for the neutral blue form which contains no unpaired electrons. Relatively high third order susceptibility and hyperpolarizability values of the order of 10−10 and 10−28 esu were obtained for both the green and blue forms, respectively. A very low threshold intensity of 0.00051 J cm−2 was obtained for the blue form. Hence the complex shows promise for non-linear optical applications.