Q-band Maximum Research Articles

Inducing ring distortions in unsubstituted metallophthalocyanines using axial N-heterocyclic carbenes.

A series of metallophthalocyanine (PcM) complexes with axial N-heterocyclic carbene ligands (NHC; 1,3-diisopropylimidazol-2-ylidene (DIP) and 1,3-dimethylbenzimidazol-2-ylidene (DMB)) were prepared and structurally characterized. PcCoII(DIP), PcZnII(DIP), and PcZnII(DMB) are five-coordinate complexes with mild dome-type Pc-ring distortions, while PcFeII(DIP)2 is six-coordinate and has a very large ruffle-type ring-distortion with respect to typical PcM(L)2 systems. The distortion is induced by the highly steric axial DIP ligands. The distortions were quantified and classified by their bond lengths and torsion angles, and according to the normal-coordinate structural decomposition (NSD) analysis. Upon ligation of the NHC, the insoluble PcM materials were solublized in common organic solvents, with typical UV-visible Q-band maxima observable between 658 and 677 nm; the increased solubility is rationalized in terms of the reduced solid-state aggregation of the complexes, attributable to the axial ligation.

Synthesis of peripherally substituted aza-analogues of Si(IV) phthalocyanines by complexation method

Despite many notes about advantageous properties of Si(IV) phthalocyanines, their aza-analogues from the group of tetrapyrazinoporphyrazines (TPyzPzs) are only rarely reported in the literature, especially for macrocycles carrying peripheral groups. Thus, a series of Si(IV) TPyzPzs having alkylamino, aryloxy, alkylsulfanyl or alkyl group at the periphery was prepared by complexation of Si(IV) into corresponding metal-free derivatives by their stirring at 30[Formula: see text] C with trichlorosilane, using tributylamine as a base, and dichloromethane as a solvent. Key factors affecting the feasibility of this method, such as well-chosen excess of trichlorosilane and solvent used, were described. The model compound of the series ([Formula: see text], aryloxy substituted dihydroxy Si(IV) TPyzPz) was then modified at axial positions using trihexylchlorosilane as a ligand. All target Si(IV) TPyzPzs showed strong absorption with Q-band maxima ranging 617–655 nm (extinction coefficients 82 000–341 000 L⋅mol[Formula: see text]⋅cm[Formula: see text] and efficient fluorescence emission with [Formula: see text] values ranging 0.32–0.44 with the exception of alkylamino substituted TPyzPz, whose excited states were efficiently quenched by intramolecular charge transfer. The possibility of axial modification, good spectral and fluorescence properties as well as the ability to quench the excited states upon introduction of alkylamine groups indicate the suitability of these derivatives for fluorescence sensing applications.

Decreasing the aggregation and ligand redox potential of metallophthalocyanines through branched ether functionalization

The addition of ether functional groups to a metallophthalocyanine ring is known to significantly decrease the oxidation potentials of the ring. In this light, the impact of the branching of alkyl-ether groups on the electronic properties was investigated via the synthesis of non-peripheral ([Formula: see text]-substituted n-butyl (1), iso-butyl (2) and sec-butyl (3) 1,4,8,11,15,18,22,25-octabutoxyphthalocyanines, in conjunction with Co and Cu metal centers. From 1 to 3 the first and second ring-based oxidation potentials were decreased by 70 mV and 110 mV respectively both for Cu and Co-containing complexes; the UV-visible Q-band maxima only changed by 4-8 nm, consistent with the destabilization of both the HOMO and LUMO, as confirmed by TD-DFT calculations. The reversibility of both redox couples was improved via branching (3) for the Co complexes. All six complexes were structurally characterized, with varying levels and types of ring distortions. All molecules show 1-D supramolecular stacking, but for n-butoxy 1Co an intermolecular Co-O interaction aligns the molecular stacks, while for sec-butoxy 3Co only [Formula: see text]-[Formula: see text] stacking of the Pc-ring was present. Both 3Co and 3Cu were ring-oxidized at lower potentials than 1Co and 1Cu, and the increased steric bulk from the branched ether chains prevented the overlap of their N8C8 inner rings.

Synthesis, Spectroscopy, Electrochemistry and DFT of Electron-Rich Ferrocenylsubphthalocyanines.

A series of novel ferrocenylsubphthalocyanine dyads Y-BSubPc(H)12 with ferrocenyl-carboxylic acids Y-H = (FcCH2CO2-H), (Fc(CH2)3CO2-H) or (FcCO(CH2)2CO2-H) in the axial position were synthesized from the parent Cl-BSubPc(H)12 via an activated triflate-SubPc intermediate. UV/Vis data revealed that the axial ferrocenyl-containing ligand did not influence the Q-band maxima compared to Cl-BSubPc(H)12. A combined electrochemical and density functional theory (DFT) study showed that Fe group of the ferrocenyl-containing axial ligand is involved in the first reversible oxidation process, followed by a second oxidation localized on the macrocycle of the subphthalocyanine. Both observed reductions were ring-based. It was found that the novel Fc(CH2)3CO2BSubPc(H)12 exhibited the lowest first macrocycle-based reduction potential (−1.871 V vs. Fc/Fc+) reported for SubPcs till date. The oxidation and reduction values of Fc(CH2)nCO2BSubPc(H)12 (n = 0–3), FcCO(CH2)2CO2BSubPc(H)12, and Cl-BSubPc(H)12 illustrated the electronic influence of the carboxyl group, the different alkyl chains and the ferrocenyl group in the axial ligand on the ring-based oxidation and reduction values of the SubPcs.

Novel d- and f-metal phthalocyaninates based on 4-(2,4,5-trichlorophenoxy)phthalonitrile. Synthesis, spectroscopic and fluorescent properties

The work reports synthesis and spectroscopic-luminescent properties of first obtained zinc, magnesium, erbium and gadolinium trichlorophenoxy-phthalocyanine complexes. The initial building unit being 4-(2,4,5-trichlorophenoxy)phthalonitrile is synthesized by nucleophilic substitution reaction. Zinc and magnesium complexes are obtained by template condensation of the phthalodinitrile and corresponding acetates. A demetallization of magnesium phthalocyaninate results in the formation of free tetra-4-(2,4,5-trichlorophenoxy)phthalocyanine ligand. Rare-earth element complexes are synthesized by two approaches: template condensation and metallization of free phthalocyanine ligand. The planar complex is found to be yielded higher in case of template fusion. Influence of lanthanide salts anion (acetate, chloride) on formation ability of sandwich-type complex is analyzed. A double-decker complex is testified to be formed only upon the template fusion of gadolinium acetate with 4-(2,4,5-trichlorophenoxy)phthalonitrile. The as-obtained compounds are studied in terms of spectral-luminescent characteristics. A bathochromic shift of absorption Q-band maximum is found to accompany d-to-f-metal transition. The zinc complex being associated in chloroform exhibits higher quantum yield of fluorescence than monomeric forms generated upon addition of organic ligand.

Preparation of phthalocyanine-bound myristoyl celluloses for photocurrent generation system

The influences of two structural modifications on the photocurrent generation performance of the Langmuir–Blodgett (LB) film of the 6-O-phthalocyaninyl cellulose derivative were investigated. These structural modifications were the substituent groups at the O-2 and O-3 positions, and the central metal of the phthalocyanine moiety. Specifically, 6-O-Zn/phthalocyaninyl- (8a) and Pd/phthalocyaninyl (8b) -2,3-di-O-myristoylcelluloses were prepared instead of 6-O-Zn/phthalocyaninyl-2,3-di-O-myristylcellulose (2). The LB monolayer film of compound 8a on an indium thin oxide electrode showed higher photocurrent generation performance than that of compound 2. This suggested that myristoyl groups (C-14 acyl groups) were more beneficial to photocurrent generation than myristyl groups (C-14 alkyl groups), as the substituent at the O-2 and O-3 positions. The LB monolayer film of compound 8b showed photocurrent generation from 500 to 700 nm, although a blue-shift in the Q-band maximum was observed. The photocurrent generation performance of compound 8b was significantly higher than that of compound 8a. This indicated that Pd was more beneficial to photocurrent generation than Zn. The film of compound 8b prepared by the horizontal lifting method showed better photocurrent generation performance than that prepared by the vertical dipping method. Consequently, compound 8b is a complementary material to the porphyrin-appended cellulose derivative (1) for photocurrent generation system.

OFF-ON-OFF Red-Emitting Fluorescent Indicators for a Narrow pH Window.

A unique combination of two independent mechanisms of fluorescence quenching, namely intramolecular charge transfer (ICT) from a peripheral donor and protonation of azomethine nitrogen atoms in zinc tetrapyrazinoporphyrazines (TPyzPz), provides a new possibility for sensing pH in a specific range. The pH selectivity was controlled by the different basicities of the donor for ICT (dimethylaminoaryl), which was connected to the macrocycle by π-extended linkers of different lengths. ICT and protonation have been studied in detail by photophysical, spectral (UV/Vis and MCD spectra), and electrochemical measurements, and further supported by theoretical calculations (DFT, TDDFT). The pH-sensing properties of the TPyzPzs have been investigated in THF and in water after anchoring the TPyzPzs to liposomes. The salient pKa values were around 1.3 (azomethine nitrogen) and 2.29-4.76 (donor for ICT). The lead indicators (sensing over a pH range of 1.0-2.5) with fairly steep sensing profiles exhibited increases in fluorescence between the OFF/ON states of more than 20-fold and strong absorption in the red region (Q-band maximum >650 nm, ϵ≈2×106 m-1 cm-1 ).

Electrochemical Evidence of Intramolecular Electronic Communication in Zr and Hf Phthalocyanines Bearing Ferrocene-Containing β-Diketonato Axial Ligands: Structure of [PcHf(FcCOCHCOC6H5)2

The series of zirconium(IV) and hafnium(IV) phthalocyanine complexes [PcM(FcCOCHCOR)2] (Pc = phthalocyaninato; M = Zr; R = CF3 (1), CH3 (2), C6H5 (3), Fc ((C5H5)Fe(C5H4), 4), as well as M = Hf ; R = CF3 (5), CH3 (6), C6H5 (7), and Fc (8)) were synthesized. A single-crystal X-ray diffraction analysis of the structure of [PcHf(FcCOCHCOC6H5)2], 7 (Z = 2, space group P1), showed the two axial β-diketonato ligands were orientated in such a way that the ferrocenyl groups were positioned diagonally opposite each other. From the structural determination of 7 it was clear that these complexes have a distorted D4h symmetry at the coordination site of the metal centers, which explains a splitting of the UV-vis Q band into Qx and Qy components with 3 ≤ Δλ(max,Q) ≤ 10 nm. Cyclic and square wave voltammetric studies in CH2Cl2/[N((n)Bu)4][B(C6F5)4] allowed observation of at least three phthalocyaninato macrocycle-based redox couples as well as all (i.e., two or four) well-resolved ferrocenyl couples in 1-8. For M = Zr and R = Fc, formal reduction potentials of the four ferrocenyl groups were found to be E°' = 296, 386, 538, and 687 mV versus free ferrocene. Spectroelectrochemical evidence, UV-vis Q-band maximum wavelengths, and HOMO-LUMO energy gaps as expressed by ΔE°'I-III = ΔE°'wave I - ΔE°'wave III were mutually consistent, indicating that the first phthalocyaninato ring-based oxidation occurs before ferrocenyl oxidations take place. The potential for each redox process was found to be dependent on the sum of β-diketonato R-group group electronegativities, ΣχR. Mathematical relationships for the dependency of E°' on ΣχR for all four observed ring-based redox processes as well as for the ferrocenyl-based redox processes were determined. This allowed prediction of potentials for redox processes that fall outside the workable potential window of the solvent. No significant differences were found between the corresponding redox potentials of zirconium and hafnium analogues bearing the same axial ligands.

Synthesis, spectral and electrochemical properties of a novel phosphorous(V)-phthalocyanine

A novel phosphorous(V)-phthalocyanine, [ P ( tppc )( OH )( O )], where tppc denotes tetrakis{(2′,6′-dimethyl)phenoxy}phthalocyaninate, has been synthesized and its spectral properties in non-aqueous and aqueous media have been investigated. This compound has been found free from aggregation in EtOH whereas forms J-aggregates in CH 2 Cl 2 and acetonitrile, suggesting the presence of chemical interaction between the axial ligand and the surrounding solvent molecules. The most intense absorption band (Q-band) appears at 683 nm in EtOH , however, reaction with CF 3 COOH has given rise to a large red shift of the Q-band without lowering of its C 4 symmetry (evidenced by magnetic circular dichroism spectroscopy), indicating protonation at the axial site. Its fluorescence quantum yield has been determined (0.49 in EtOH ) and has been found much higher than those of the known Sb V or As V derivatives by more than one order of magnitude. The first reduction potential has been determined by cyclic voltammetry (-1.09 V vs. ferrocenium+/ferrocene) in CH 2 Cl 2. It is noteworthy that the Q-band maximum wavelength and the first reduction potential values are normal for conventional phthalocyanines despite the presence of pnictogen(V) in the cavity of the macrocyclic ligand.

Perfluorinated porphyrazines 1: Synthesis and UV-vis spectral study of perfluorinated octaphenylporphyrazine and its indium(III) complex, [MPA(F5Ph)8](M= 2H,InIII(OH))

Novel perfluorinated porphyrazine has been prepared as indium(III) complex of octa(pentafluorophenyl)porphyrazine by cyclotetramerization of 1,2-dicyano-1,2-bis(pentafluorophenyl)-ethylene (mixture of cis- and trans-isomers) with basic indium(III) acetate in a melt. The InIIIcomplex is stable in trifluoroacetic and sulfuric acids, but is easily demetalated with formation of the free-base in a chloroform solution containing HCl or slighly acidified with CF3COOH in the presence of tetraalkylammonium chloride as a catalyst. Perfluorination of octaphenylporphyrazine macrocycle leads to a hypsochromic shift of the Q-band maxima in the electronic absorption spectra, to drastic decrease of the basicity of meso-nitrogen atoms of porphyrazine macrocycle and to increase of the acidity of the internal NH -groups.

Study on Interaction of Cationic Porphyrazine with Synthetic Polynucleotides

Interactions of cationic tetrakis (N, N′, N″, N‴- tetramethyltetra-3, 4-pyridinoporphyrazinatozinc (II) (Zn (tmtppa)) with synthetic polynucleotides, poly (G-C) and poly (A-T), and calf thymus DNA have been characterized in 7.5 mM phosphate buffer of pH 7.2 by UV-Vis absorption and fluorescence spectroscopy. The appearance of hypochromicity more than 30% in UV-Vis spectra of porphyrazine due to interaction of both poly (G-C) and poly (A-T) indicates interaction similar to that of porphyrazine with DNA.The binding constants were determined from the changes in the Q-band maximum of the porphyrazine spectra at various poly (G-C) and DNA concentrations. The values of K were 2.5 × 106M−1, 2.5 × 106M−1and 2.5 × 105M−1for poly (G-C), poly (A-T) and DNA, respectively, at 25°C. The thermodynamic parameters (ΔG°, ΔH°, ΔS°) were calculated using the van't Hoff equation at various temperatures. The enthalpy and entropy changes were determined to be 41.14 kJ mol−1and 260.50 J mol−1·K−1for poly (G-C) and 53.59 kJ mol−1and 285.46 J mol−1·K−1for DNA at 25°C. The positive and large values of the entropy and enthalpy suggest that both hydrophobic and electrostatic interactions may play an important role in the stabilization of the complex formation. The binding of polynucleotides to porphyrazine quenches fluorescence emission of ethidium bromide (EB), and the quenching process obeys linear Stern-Volmer relationship. The results reviled groove-binding mode of porphyrazine for both AT- and GC-rich polynucleotides of DNA.

Study on interaction of cationic porphyrazine with synthetic polynucleotides.

Interactions of cationic tetrakis (N, N′, N″, N‴- tetramethyltetra-3, 4-pyridinoporphyrazinatozinc (II) (Zn (tmtppa)) with synthetic polynucleotides, poly (G-C) and poly (A-T), and calf thymus DNA have been characterized in 7.5 mM phosphate buffer of pH 7.2 by UV-Vis absorption and fluorescence spectroscopy. The appearance of hypochromicity more than 30% in UV-Vis spectra of porphyrazine due to interaction of both poly (G-C) and poly (A-T) indicates interaction similar to that of porphyrazine with DNA.The binding constants were determined from the changes in the Q-band maximum of the porphyrazine spectra at various poly (G-C) and DNA concentrations. The values of K were 2.5 × 10 M, 2.5 × 10 M and 2.5 × 10 M for poly (G-C), poly (A-T) and DNA, respectively, at 25°C. The thermodynamic parameters (ΔG°, ΔH°, ΔS°) were calculated using the van't Hoff equation at various temperatures. The enthalpy and entropy changes were determined to be 41.14 kJ mol and 260.50 J mol·K for poly (G-C) and 53.59 kJ mol and 285.46 J mol·K for DNA at 25°C. The positive and large values of the entropy and enthalpy suggest that both hydrophobic and electrostatic interactions may play an important role in the stabilization of the complex formation. The binding of polynucleotides to porphyrazine quenches fluorescence emission of ethidium bromide (EB), and the quenching process obeys linear Stern-Volmer relationship. The results reviled groove-binding mode of porphyrazine for both AT- and GC-rich polynucleotides of DNA.

Spectral, photophysical and photochemical properties of tetra- and octaglycosylated zinc phthalocyanines

Photophysical and photochemical properties of a series of tetra- and octaglycosylated zinc phthalocyanines (ZnPcs) substituted with glucose and galactose moieties have been reported. Spectral properties of these phthalocyanines are compared in DMSO. Absorption spectra of the non-peripherally tetra-substituted ZnPcs 2 showed a significant red shift in their Q-band maxima as compared to the peripherally substituted analog 1. All the complexes gave high triplet quantum yields ranging from 0.68 to 0.88, whereas triplet lifetimes were in the range of 100-430 μs in argon-saturated solutions. The octagalactosylated ZnPc 3b showed the highest triplet quantum yield and singlet oxygen quantum yield of 0.88 and 0.69, respectively. The fluorescence quantum yields and lifetimes of all the compounds under investigation were within the range of zinc phthalocyanine complexes.

Photophysical and photochemical behavior of electrospun fibers of a polyurethane polymer chemically linked to lutetium carboxyphenoxy phthalocyanine

A phthalocyanine complex of lutetium substituted with four peripherally substituted 4-carboxyphenoxy groups was synthesized using cyclotetramerisation reaction. Its structure was elucidated using conventional spectroscopic methods and elemental analysis. The spectral behavior of the complex was studied in DMF solution and in a solid polyurethane fiber matrix. The UV-Visible spectrum showed a red shift in its Q-band maximum absorption within the fiber as compared to that in solution. The triplet quantum yield in DMF was determined to be 0.51 with a lifetime of 2.7 μs and a singlet oxygen quantum yield of 0.33 with a lifetime of 19.85 μs in the same solvent. The functionalized phthalocyanine fiber could be a promising fabric material for applications such as self-disinfecting in wound dressing. A method based on the conversion of ADMA was used to estimate the singlet oxygen quantum yield of the Pc in the hybrid fiber. An estimated singlet oxygen quantum yield value of 0.11 in aqueous medium was obtained. The fluorescence quantum yield of the Pc was found to be 0.01 with a lifetime of 3.20 ns in DMF.

Synthesis and characterization of novel soluble phthalocyanines with fused conjugated unsaturated groups

The synthesis, characterization, voltammetric and spectroelectrochemical properties of a novel tetra-cationic metallophthalocyanine (M = Zn) containing four Schiff’s base substituents attached directly on peripheral positions have been presented in this work. The new compounds have been characterized by using elemental analysis, FTIR, 1H NMR, UV–Vis and MALDI-TOF MS spectroscopic data. The electrochemical, in-situ spectroelectrochemical, and in-situ electrocolorimetric measurements on precursors and end products confirm that the complexes exhibit extra electron transfer reaction assignable to the electroactive nitro, amine and Schiff’s base groups in addition to the common Pc ring-based processes. Extra conjugation of amine and cinnamaldehyde groups causes both a bathochromic shift (ca. 30 nm) in Q-band maxima and a lower redox potential (ca. −400 mV) in CV measurements.

Dynamics of redox processes and electrochromism of films of zirconium (IV) phthalocyanines with out-of-plane β-dicarbonyl ligands

The electrochromic properties of the mixed-ligand zirconium phthalocyanine complex films have been investigated. Voltammetric characteristics, absorption spectra of films as a function of potential, and curves of current and absorption at the Q-band maximum in the case of their reversible oxidation in 1 N KCl against time have been measured. An analysis of the time-current dependence allowed us to find that the dynamics of the reversible oxidation of phthalocyanine complexes in such films are determined by the codiffusion in their bulk of positive and negative carriers (as Cl − anions) with effective diffusion coefficient D eff = ~ 10 − 13 cm 2/s. The same value of D eff has been obtained from measurements of the curve of optical density in the region of the Q-band maximum against time.

Synthesis and Spectroscopic and Electrochemical Studies of Pyrazine- or Pyridine-Ring-Fused Tetraazachlorins, Bacteriochlorins, and Isobacteriochlorins

Mixed condensation of tetramethylsuccinonitrile and either 2,3-dicyano-5,6-diethylpyrazine, 2,3-dicyanopyridine, or 3,4-pyridinedicarboximide in the presence of nickel chloride forms novel pyrazine-, 2,3-pyridine-, or 3,4-pyridine-ring-fused tetraazachlorin (TAC), tetraazabacteriochlorin (TABC), and tetraazaisobacteriochlorin (TAiBC) derivatives. All possible structural isomers were separated using repeated thin-layer chromatography and have been investigated by absorption and magnetic circular dichroism spectroscopy. Similarly to previously reported TAC analogues, the TAC and TABC derivatives show large splitting of the Q band, while a single, intense absorption band is observed for the TAiBC derivatives. Although the absorption spectra are practically identical in shape for the separated structural isomers of TACs and TABCs, the Q-band maxima of the TAiBCs depend significantly on their structures. The observed spectroscopic properties were interpreted on the basis of electrochemical data and the results of (time-dependent) DFT calculations.

Synthesis and electrochemical properties of purple manganese(III) and red titanium(IV) phthalocyanine complexes octa-substituted at non-peripheral positions with pentylthio groups

The synthesis and electrochemical characterisation of octapentylthiophthalocyaninato manganese(III) acetate ( 4) and octapentylthiophthalocyaninato titanium(IV) oxide ( 5) complexes are reported. The complexes have an unusual purple ( 4) and red ( 5) colouration since the Q-band is shifted to the near infra red region with Q-band maxima at 893 nm and 808 nm in dichloromethane for 4 and 5, respectively. The structures of the complexes were confirmed by elemental analysis and interpretation of their spectroscopic data, including 2D NMR. The cyclic voltammetry (CV) of the Mn complex ( 4) showed four quasi reversible couples. The reduction processes are attributed to Mn IIIPc −2/Mn IIPc −2 and Mn IIPc −2/Mn IIPc −3 and the oxidation processes to Mn IVPc −2/Mn IIIPc −2 and Mn IVPc −1/Mn IVPc −2. The processes were confirmed by spectroelectrochemistry. A well-defined spectrum of the rare Mn IVPc −2 species is reported. The CV of the Ti complex ( 5) showed two well-resolved reduction processes due to Ti IVPc −2/Ti IIIPc −2 and Ti IIIPc −2/Ti IIPc −2. However, oxidation processes of the complex revealed adsorption behaviour and resulted in decomposition on electrolysis using spectroelectrochemistry.

Thermodynamic and spectroscopic study on the binding of cationic Zn(ii) and Co(ii) tetrapyridinoporphyrazines to calf thymus DNA: the role of the central metal in binding parameters

Binding of water-soluble N,N′,N″,N‴-tetramethyltetra-3,4-pyridinoporphyrazinatozinc(II) {[Zn(3,4-tmtppa)]4+} and N,N′,N″,N‴-tetramethyltetra-3,4-pyridinoporphyrazinatocobalt(II) {[Co(3,4-tmtppa)]4+} with calf thymus DNA has been investigated in 1 mM phosphate buffer and 5 mM NaCl at low ionic strength by UV-vis, fluorescence, and circular dichroism (CD) spectroscopic techniques, and also by the viscometric method. The appearance of a dramatic hypochromicity without any shift in the Q-band maximum of Zn(tmtppa) in the presence of DNA and a positive ellipticity in the visible CD of this porphyrazine complexed with DNA are definitive evidence of outside binding of this complex. It can be assumed that [Zn(3,4-tmtppa)]4+ in water is axially ligated by one H2O molecule. Therefore, this complex is inhibited from intercalation and binds externally. The interaction of [Co(3,4-tmppa)]4+ with DNA causes a decrease of the absorbance in the Q-band region of porphyrazine and a large red-shift. The visible CD of Co(tmtppa) complexed with DNA manifests a pattern of bisignate CD spectra, which possibly lead us to the coexistence of intercalation and outside binding modes. The binding constants were determined from the changes in the Q-band maximum of the porphyrazine spectra using SQUAD software. The values of K were (8.9 ± 0.3) × 104 and (2.3 ± 0.0) × 105 M−1 for [Co(3,4-tmtppa)]4+ and [Zn(3,4-tmtppa)]4+, respectively, at 27 °C. The higher affinity of the zinc complex towards DNA with respect to the cobalt complex was attributed to the coordination interaction as the major contributing factor, which enables superior interaction of the zinc complex with the DNA duplex. The thermodynamic parameters (ΔG°, ΔH°, ΔS°) were calculated from the van't Hoff equation at various temperatures. The enthalpy and entropy changes were determined to be: +39.6 ± 3.0 kJ mol−1 and +226.7 ± 10.5 J mol−1 K−1 for [Co(3,4-tmtppa)]4+ and +44.0 ± 3.3 kJ mol−1 and +249.6 ± 11.3 J mol−1 K−1 for [Zn(3,4-tmtppa)]4+. The positive and large values of the entropy and enthalpy suggest that both hydrophobic and electrostatic interactions may play an important role in the stabilization of the complex. The influence of the ionic strength was investigated. It was concluded that the apparent binding constants decrease with increasing [Na+] as predicted. Titration of DNA with Zn(tmtppa) produces moderate decreases in the solution-reduced viscosity (SRV), indicative of outside binding. The increase in the viscosity of DNA in the presence of the cobalt complex is related to the lengthening of the DNA helix due to the intercalation. The quenching of the DNA–ethidium bromide complex by the above-mentioned porphyrazines was investigated. The values of the quenching constants (KSV) and the rate constants of the quenching (kq) were determined by the Stern–Volmer equation.

Synthesis, Photochemistry, and Electrochemistry of a Series of Phthalocyanines with Graded Steric Hindrance

A group of twelve new and three known silicon phthalocyanines having axial ligands and peripheral groups which provide varying amounts of steric protection to the ring face and ring periphery has been assembled. These are SiPc[OSi(n-C6H13)3]2, 1, (known), SiPc[OSi(i-C4H9)2(n-C18H37)]2, 2, SiPc(OEt)8[OH]2, 5, SiPc(OEt)8[OSi(CH3)3]2, 6, SiPc(OnBu)8[OH]2, 8, (known), SiPc(OnBu)8[OSi(n-C6H13)3]2, 9, (known), SiPc(OnBu)8[OSi(i-C4H9)2(n-C18H37)]2, 10, SiPc(dib)4(OnBu)8[OH]2, 15, SiPc(dib)4(OnBu)8[F]2, 16, SiPc(dib)4(OnBu)8[OSi(n-C6H13)2]2, 17, SiPc(dib)4(OnBu)8[OSi(i-C4H9)2(n-C18H37)]2, 18, SiPc(dib)4(OnBu)8[OSi8O12(C5H9)7]2, 19, SiPc(dib)4(OnBu)8[OH]2, 22, SiPc(dib)4(OiBu)8[OSi(n-C6H13)3]2, 23, and SiPc(dib)4(OiBu)8[OSi8O12(C5H9)7]2, 24. Syntheses are given for the twelve members of the group that are new. Photophysical and voltammetric investigations of six representative members of the group, 1, 2, 10, 18, 19, and 24, have been carried out. The results show that compounds 1 and 2 (no butoxy substituents at the 1 and 4 positions) have significantly larger values of the first oxidation potential (E+1) than those compounds (10, 18, 19, and 24) that do carry these substituents. The values of E-1 (first reduction potential) show very little in the way of structural dependence. Alkoxy substitution at the 1,4 positions affects the HOMO energies, and therefore, the addition of an electron from an electrode to the LUMO of a 1,4 substituted silicon phthalocyanine will not be a sensitive function of the substitution pattern. The removal of an electron from the HOMO in an oxidation step on the other hand would be expected to be energetically less demanding for those compounds wherein the HOMO is higher lying. This orbital energy effect of substitution makes it clear why the E+1 values for compounds 1 and 2 are significantly lower. Substitution of dibenzobarreleno (dib) at the 2,3 positions has only minor effects on the HOMO energy, as shown by the similarities in the position of the Q-band maximum. However, it is very likely that the steric effects of the dibenzobarreleno substituents and the [OSi8O12(C5H9)7] axial cages contribute to the observed trends in E+1. Bimolecular rate constants for quenching of the triplet states of the six target compounds by O2, by β-carotene, and by chloranil were measured. The first two compounds quench by triplet−triplet (TT) energy transfer, whereas the last is an electron transfer (ET) reactant. All rate parameters were sensitive to the steric crowding of the phthalocyanine π system, but with different degrees. The least sensitive was the ET reaction with chloranil. Thus, it appears that although steric crowding of the triplet state of the silicon phthalocyanines is very effective at reducing the rate constants of exoergic electron exchange energy transfer (TT) reactions, even for a small molecule such as oxygen, it is much less effective at discriminating against electron transfer (ET) processes. These differences may be accounted for on the concept that the overlap requirement for the double electron exchange of TT energy transfer is more stringent compared to the single electron transfer (ET).