ZnPc Derivatives Research Articles

Catalytic and Selective Red Light-Triggered Photodegradation of a G-Quadruplex DNA by a Zinc (II) Phthalocyanine.

Water-soluble phthalocyanine (Pc) derivatives have been regarded as potential G-quadruplex (G4) nucleic acid-targeting ligands for anticancer therapy and have been extensively studied as effective photosensitizers for photodynamic therapy (PDT). Understanding how photosensitizers interact with nucleic acids and the subsequent photolytic reactions is essential for deciphering the initial steps of PDT, thereby aiding in the development of new photosensitizing agents. In this study, we found that red-light irradiation of a mixture of a Zn(II) Pc derivative and an all-parallel G4 DNA leads to catalytic and selective photodegradation of the DNA by reactive oxygen species (ROS) generated from the Zn(II) Pc derivative bound to DNA through a reaction mechanism similar to that of an enzyme reaction. This finding provides a novel insight into the molecular design of a photosensitizer to enhance its PDT efficacy.

The phenoxy-bearing naphthalimide substituted phthalocyanines: Photophysicochemical and biological properties

A new Si(IV) phthalocyanine (Pc) (1) derivative comprising axially phenoxy-bearing naphthalimide and peripherally t-butyl groups was synthesised and the photophysicochemical properties of this compound were investigated as an antioxidant and antimicrobial agent. Furthermore, the biological properties of the Si(IV) Pc compound (1) and its Zn(II) and Ga(III) Pc derivatives with a peripherally attached phenoxy-bearing naphthalimide group(2 and 3) were assessed in this study. While these compounds exhibited moderate antioxidant effects, their DNA nuclease activities were highly satisfactory. The compounds demonstrated effective antimicrobial activity, particularly following the photodynamic therapy. The most effective minimum inhibitory concentration value was obtained as 4 mg/L against E. faecalis and S. aureus. All compounds inhibited 100 % microbial cell viability at 125 mg/L. The biofilm formation ability of P. aeruginosa and S. aureus was significantly inhibited by all of the Pc compounds. Furthermore, experimental data were supported by TD-DFT calculations and NTO analyses, and the orbital densities of the compounds were shown.

Ethylenediamine control of the solid-state supramolecular chemistry of zinc phthalocyanine

The two axially ligated H-shaped and T-shaped zinc phthalocyanine derivatives, ZnPc(EDA)ZnPc and ZnPc(EDA), were obtained directly by thermal reaction of ZnPc in ethylenediamine (EDA) solution. Both complexes, ZnPc(EDA)ZnPc and ZnPc(EDA), co-crystallize with the EDA and water molecules yielding good-quality single crystals [ZnPc(EDA)ZnPc][ZnPc(EDA)]2∙2EDA·6H2O − 1. The interaction of Zn center of ZnPc with the axial substituent containing lone electron pair on NH2 groups with zinc phthalocyanine in both zinc phthalocyanine derivatives, ZnPc(EDA)ZnPc and ZnPc(EDA), leads to a deviation of Zn from the centre of cavity by 0.442(3) and 0.514(3) Å in the T- and H-shaped molecules as well as causes, as expected, the deformation of the planar molecule ZnPc into a saucer-shape conformation. Thus, in both types of molecules the central Zn atom of ZnPc complexes with EDA molecule exhibits 4 + 1 coordination formed by the four isoindole nitrogen atoms of the Pc macrocycle at the equatorial position and the nitrogen atom of the amino group of the EDA molecule at the axial position. Supramolecular arrangement of the T-shaped and H-shaped ZnPc-derivatives in crystal is characterized by a reduction of π···π interactions and an improvement in inter-system crossing in relation to parent ZnPc, and is controlled by the NH∙∙∙O, NH∙∙∙N and OH∙∙∙O hydrogen bonds formed between the T- and H-shaped molecules and lattice EDA and water molecules, which results in increase its solubility and improved photophysical and photochemical properties. The aggregation behaviour of T- and H-shaped ZnPc derivatives building crystals 1 in solutions was investigated by UV–Vis spectroscopy. In order to support and verify the experimental results, the DFT and time-dependent (TD) DFT calculations were performed.

Thiopyridinium phthalocyanine for improved photodynamic efficiency against pathogenic fungi

The emergence of opportunistic pathogens and the selection of resistant strains have created a grim scenario for conventional antimicrobials. Consequently, there is an ongoing search for alternative techniques to control these microorganisms. One such technique is antimicrobial photodynamic therapy (aPDT), which combines photosensitizers, light, and molecular oxygen to produce reactive oxygen species and kill the target pathogen. Here, the in vitro susceptibilities of three fungal pathogens, namely Candida albicans, Aspergillus nidulans, and Colletotrichum abscissum to aPDT with zinc(II) phthalocyanine (ZnPc) derivative complexes were investigated. Three ZnPc bearing thiopyridinium substituents were synthesized and characterized by several spectroscopic techniques. The Q-band showed sensitivity to the substituent with high absorptivity coefficient in the 680-720nm region. Derivatization and position of the rings with thiopyridinium units led to high antifungal efficiency of the cationic phthalocyanines, which could be correlated with singlet oxygen quantum yield, subcellular localization, and cellular uptake. The minimum inhibitory concentrations (MIC) of the investigated ZnPc-R complexes against the studied microorganisms were 2.5μM (C. albicans) and 5μM (A. nidulans and C. abscissum). One ZnPc derivative achieved complete photokilling of C. albicans and, furthermore, yielded low MIC values when used against the tolerant plant-pathogen C. abscissum. Our results show that chemical modification is an important step in producing better photosensitizers for aPDT against fungal pathogens.

Asymmetrical zinc(II) phthalocyanines cobalt tungstate nanomaterial conjugates for photodegradation of methylene blue

Herein, we present syntheses of three asymmetrical zinc(II) phthalocyanine (ZnPc) complexes and hydrothermal synthesis of cobalt tungstate nanoparticles. The ZnPc derivatives were covalently linked to cobalt tungstate nanoparticles. Photophysical and photochemical behaviour of Pcs and nanoconjugates were investigated. The nanoconjugates generated higher triplet quantum yield and singlet oxygen quantum yield than the ZnPcs alone. Furthermore, in this paper photocatalytic efficiencies of ZnPc complexes and nanoconjugates were investigated for the degradation of methylene blue and higher photocatalytic behaviour was observed for the conjugates. The kinetic model was used to study photocatalytic behaviour of all the prepared photocatalysts.

Solution-processed small-molecule organic solar cells based on non-aggregated zinc phthalocyanine derivatives: A comparative experimental and theoretical study

A series of non-aggregated zinc phthalocyanine derivatives containing either bulky thiophenol or phenol substituents were synthesized as a novel donor component for bulk heterojunction (BHJ) solar cell applications. The molecular structure and photophysical properties of ZnPc derivatives were investigated by combined experimental and theoretical studies using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. In order to evaluate the physical properties of ZnPcs in the solvent environment, we applied the conductor-like polarizable continuum model (CPCM). Within this scope, light-harvesting efficiency (LHE), excited-state lifetime (τ), maximum absorption wavelengths (λmax), oscillator strength (f) and hyperpolarizability (β tensors) were calculated both in vacuum and chloroform (ε = 4.9) medium. Furthermore, divergent types of global descriptors such as EHOMO, ELUMO, and bandgap (Egap) energies, ionization potential (I), electron affinity (A), hardness (η), and electrophilicity index (ω) were also calculated. Our computational findings revealed that the linker heteroatoms [sulfur for the ZnPc (1–2); oxygen for the ZnPc (3–4) including the substituent type (isopropyl for the ZnPc (2–4), and phenyl for the ZnPc (1–3] severely affected the photophysical properties of the dyes. In relation, theoretical results are in good accordance with our experimental observations. Finally, ZnPc derivatives were used as a donor component and PC61BM as an acceptor material in BHJ solar cells, displaying a maximum power conversion efficiency of 0.8%. Compared with ZnPcs 1–2, ZnPc 3–4 based cells showed an inferior photovoltaic performance. These results are promising and should encourage further studies on BHJ solar cells using near-infrared absorbing and non-aggregated ZnPcs.

Imidazole substituted Zinc(II) phthalocyanines for co-catalyst-free photoelectrochemical and photocatalytic hydrogen evolution: influence of the anchoring group.

Novel zinc phthalocyanine derivatives, ZnPc-1 and ZnPc-2, consisting of one and four imidazole units, respectively, have been synthesized and utilized as panchromatic photosensitizers for photocatalytic and photoelectrochemical H2 evolution. The effect of the imidazole-anchoring group on the photocatalytic H2 production has been compared with ZnPc-3, which possesses a carboxylic acid unit as the anchoring group. ZnPc-1/TiO2 shows the best photoactivity with the highest H2 evolution rate of 0.4006 mmol g-1 h-1, which is much higher than that of ZnPc-2/TiO2 and ZnPc-3/TiO2 (0.3319 mmol g-1 h-1 and 0.3555 mmol g-1 h-1, respectively). After 20 h of irradiation, ZnPc-1 produces an H2 production rate of 3.4187 mmol g-1 with a turnover number (TON) of 14863 and a solar-to-hydrogen energy (STH) conversion efficiency of 1.03%, without using a co-catalyst.

Zinc Phthalocyanine Conjugated Dimers as Efficient Dopant‐Free Hole Transporting Materials in Perovskite Solar Cells

AbstractFour ZnPc‐dimers with 2,5‐thienyl (ZnPc−th−ZnPc 1), 2,7‐fluorenyl (ZnPc−flu−ZnPc 2), 3,6‐bisthienylldiketopyrrolopyrrole (ZnPc−DPP−ZnPc 3) and 1,4‐phenyl (ZnPc−p−ZnPc 4) bridges have been studied as dopant‐free hole transporting materials (HTMs) in perovskite solar cells (PSCs). The synthesis and characterization of ZnPc−th−ZnPc 1 and ZnPc−flu−ZnPc 2 dimers are reported for the first time. Steady state and time resolved photoluminescence demonstrate the good hole‐extraction capability of these materials. The best efficiencies obtained for dimers 1, 2, 3 and 4 are 15.5 %, 15.6 %, 16.8 % and 15.7 %, respectively, without the addition of dopants. Besides, these derivatives demonstrated better stability both in dark storage conditions with a relative humidity <20 % for 500 h and at 50 °C with a relative humidity >60 % for 160 h when compared to doped spiro−OMeTAD. The push‐pull nature of dimer ZnPc−DPP−ZnPc 3 has led to the highest efficiency among the ZnPc derivatives under study demonstrating that donor‐acceptor‐donor systems can be good alternatives to commonly used materials due their energy levels, low cost and the final morphology of the hole transporting layer.

Spectroscopic characterization and photodynamic antimicrobial chemotherapy of phthalocyanine-silver triangular nanoprism conjugates when supported on asymmetric polymer membranes

Silver triangular nanoprisms were synthesized and conjugated to zinc (ZnPc) and indium (InPc) phthalocyanines prior to embedding in asymmetric membranes. Conjugation of nanoparticles increased triplet state and singlet oxygen quantum yields of the phthalocyanines as well as enhancing photodynamic antimicrobial chemotherapy (PACT) activity against bacteria (S. aureus). The ZnPc derivative showed higher PACT activity when compared to the InPc, possibly due to degradation of the latter in aqueous media.

Photoinactivation of Planktonic and Biofilm Forms of Escherichia coli through the Action of Cationic Zinc(II) Phthalocyanines

AbstractNovel water‐soluble zinc(II) phthalocyanines (ZnPc) peripherally substituted with 4‐dimethylaminopyridine (DMAP) units (ZnPc 1–2) and the corresponding quaternized derivatives (ZnPc 1 a–2 a) were synthesized and their photodynamic inactivation (PDI) efficiency against a Gram‐negative bacterium, a recombinant bioluminescent Escherichia coli strain either in planktonic or biofilm form, was investigated. The analysis of the photophysical properties revealed that the increase in the number of DMAP units on ZnPc shifted the absorption and emission band in aqueous media to the red region. The presence of multi‐positive charges on ZnPc derivatives prevented aggregation and enhances the solubility in aqueous media. The quaternized derivatives ZnPc 1 a and 2 a displayed good stability and promising efficacy to generate singlet oxygen (1O2). The affinity of the amphiphilic ZnPc 1–2 and quaternized ZnPc 1 a–2 a to planktonic bacterial cells corresponded to an average uptake of ∼106 PS molecules.CFU−1. The PDI assays conducted with planktonic cells and biofilms of E. coli show that irradiation with red or white light (150 mW.cm−2) in the presence of 20 μM of ZnPc derivatives caused an effective inactivation. ZnPc 1 a and ZnPc 2 a exhibited the highest inactivation efficiency, particularly of the planktonic form, causing a 5 log‐scale (99.99 %) reduction in bioluminescence. The inactivation factor for biofilms was 99 % (2 log). ZnPc 1 a and ZnPc 2 a can be regarded as promising photosensitizers for the photodynamic inactivation of Gram‐negative bacteria.

New zinc phthalocyanine derivatives for nitrogen dioxide sensors: A theoretical optoelectronic investigation

Zinc-phthalocyanines ZnPc derivatives including quinoleinoxy groups have been studied through DFT calculations. The most stable geometries were characterized for the unsubstituted to the tetra substituted ZnPcs. The energy gap decreased from 2.146 eV for ZnPc to 2.050 eV for ZnPcR4, in agreement with the experimental trend, and indicating the reliability of the electrochemical evaluation of LUMO and HOMO energy levels. Optical transitions computed at the CAM-B3LYP-D3 with triple zeta basis sets were found to be in good agreement with experimental values for both the B and Q bands. Subsequently, structures were also characterized for NO2 adsorbed complexes, in order to assess the potential role of ZnPc as a NO2 sensor. A clear sigma bonding chemisorption of NO2 on Zn atom is observed for all derivatives, followed by a charge transfer from the π Pc conjugated system to the Zn-NO2 moiety. More importantly, after NO2 chemisorption on ZnPc derivative a remarkable red-shift is observed in the optical spectra, particularly for NO2/ZnPcR4 complex, thus offering a good index to detect the binding of NO2. The optical spectra and the vibrational spectra can therefore be used to detect the presence of NO2 and ZnPc derivatives show appropriate properties to constitute good NO2 sensors.

Photosensitization of zinc phthalocyanine bearing 15-crown-5 ether moieties on carbon nitride for H2 production: Effect of co-existing alkali metal ions

A zinc phthalocyanine derivative (ZnPc) with one carboxyl group and three 15-crown-5 ether moieties has been synthesized and used as photosensitizer of Pt-loaded graphitic carbon nitride (Pt/g-C3N4) for visible-light-driven H2 production. By adding alkali metal ions (Li+, Na+, or K+) in the ZnPc solution before the dye-sensitization process, the photosensitization for H2 production on Pt/g-C3N4 can be improved with an increasing sequence of Li+ < Na+ < K+. Especially, the co-existing K+ ions cause the H2 production activity enhancing from 163 to 476 μmol h−1 with a turnover number (TON) from 3105 to 9067 h−1. Besides, the coexisting Li+, Na+ and K+ ions exhibiting an impressive apparent quantum yield (AQY) of 2.06%, 2.41% and 2.74% at 700 nm, respectively. All those AQY values are higher than that (1.88%) of the ZnPc-Pt/g-C3N4 without addition of alkali metal ion. The further investigation results indicate that the combination of ZnPc's 15-crown-5 ethers with ions are able to enhance the electron transfer ability and then the photoactivity for H2 production. Our finding may open a way to highly efficient dye-sensitized semiconductor-based photocatalysis for solar energy conversion by using ZnPc derivative bearing purposeful substituents which can be interacted with proper ions.

Porphyrinoids for Molecular Photovoltaics

In this contribution, hexachlorosubphthalocyanines SubPcCl6-X bearing different axial substituents (X) have been synthesized and used as novel electron acceptors in bulk-heterojunction organic solar cells. Solar cells with subphthalocyanines as the electron acceptors and PTB7-Th as the electron donor exhibit a power conversion efficiency up to 4% and an external quantum efficiency approaching 60% benefitting from significant photocurrent contribution from both electron donor and acceptor. These results indicate a promising prospect of developing non-fullerene acceptors based on subphthalocyanines and structurally related systems for highly efficient solution processed organic solar cells [1]. On the other hand, an unsymmetrical, push–pull porphyrazine derivative bearing an isoindole-4-carboxylic acid moiety (TT112) have been synthesized and incorporated in a dye-sensitized solar cell (DSSC). The device, which constitutes the first example of a porphyrazine-sensitized solar cell, exhibits a maximum power conversion efficiency of 3.4% [2]. Finally, easily accessible tetra-5-hexylthiophene-, tetra-5-hexyl-2,2’-bisthiophene-substituted zinc phthalocyanines (ZnPcs) have been employed as hole transporting materials (HTMs) in mixed-ion perovskite [HC(NH2)2]0.85(CH3NH3)0.15Pb(I0.85Br0.15)3 solar cells reaching the highest power conversion efficiency (PCE) reported so far for phthalocyanines. The resulting photovoltaic performance was strongly influenced by both, individual optoelectronic properties of ZnPcs and the aggregation of these tetrapyrrolic semiconductors in the HTM layer. The optimized devices exhibited a record PCE of 17.5% for tetra-5-hexylthiophene-based analogue under standard global AM 1.5 illumination. These results boost up the potential large-scale applications of solution-processed ZnPc derivatives as stable and economic hole-transport materials, opening new frontiers towards a realistic, efficient and inexpensive energy production [3]. [1] C. Duan, G. Zango, M. García Iglesias, F. J. M. Colberts, M. M. Wienk, M. V. Martínez-Díaz, R. A. J. Janssen, T. Torres, Angew. Chem. Int.. Ed. Engl. 2017, in press. [2] J. Fernández-Ariza, M. Urbani, M. Grätzel, M. S. Rodríguez-Morgade, M. K. Nazeeruddin, T. Torres, ChemPhotoChem 2016, DOI: 10.1002/cptc.201600004 [3] K. T. Cho, O. Trukhina, C. Roldán-Carmona, M. Ince, P. Gratia, G. Grancini, P. Gao, T. Marszalek, W. Pisula, P. Y. Reddy, T. Torres, M. K. Nazeeruddin, Adv. Energ. Mat. 2016, in press

Molecularly Engineered Phthalocyanines as Hole‐Transporting Materials in Perovskite Solar Cells Reaching Power Conversion Efficiency of 17.5%

Easily accessible tetra‐5‐hexylthiophene‐, tetra‐5‐hexyl‐2,2′‐bisthiophene‐substituted zinc phthalocyanines (ZnPcs) and tetra‐tert‐butyl ZnPc are employed as hole‐transporting materials in mixed‐ion perovskite [HC(NH2)2]0.85(CH3NH3)0.15Pb(I0.85Br0.15)3 solar cells, reaching the highest power conversion efficiency (PCE) so far for phthalocyanines. Results confirm that the photovoltaic performance is strongly influenced by both, the individual optoelectronic properties of ZnPcs and the aggregation of these tetrapyrrolic semiconductors in the solid thin film. The optimized devices exhibit PCE of 15.5% when using tetra‐5‐hexyl‐2,2′‐bisthiophene substituted ZnPcs, 13.3% for tetra‐tert‐butyl ZnPc, and a record 17.5% for tetra‐5‐hexylthiophene‐based analogue under standard global 100 mW cm−2 AM 1.5G illumination. These results boost up the potential of solution‐processed ZnPc derivatives as stable and economic hole‐transport materials for large‐scale applications, opening new frontiers toward a realistic, efficient, and inexpensive energy production.

Fluorescence behavior of nanoconjugates of graphene quantum dots and zinc phthalocyanines

Abstract Graphene quantum dots (GQDs) and zinc phthalocyanines interactions in different modes (covalent and non-covalent) are reported in this study. GQDs were covalently attached to the following complexes: zinc tetraamino phthalocyanine (ZnTAPc) via amide coupling, zinc tetracarboxyphenoxy Pc (ZnTCPPc) (π–π interaction) and cationic zinc tetrapyridiloxy Pc (ZnTmPyPc) (ionic interaction). GQDs fluorescence was quenched in the presence of the ZnPc derivatives. The nanoensembles of GQDs–ZnPcs showed stimulated emissions of the ZnPcs. The suggested quenching mechanism is through Forster resonance energy transfer (FRET). These novel nanoensembles hold promise for various optical and luminescence based applications.

Asymmetric zinc phthalocyanines with large steric hindrance as efficient red/near-IR responsive sensitizer for dye-sensitized solar cells

Asymmetric ZnPc derivatives with two carboxyl and six diphenylphenoxy or diphenylthiophenol groups were synthesized as dye of DSSCs. Those ZnPcs exhibit strong red/near-IR light absorption, and Zn-tri-PcNc-5 with six diphenylthiophenol groups shows obvious redshift in the Q-band and enhanced absorbance compared to Zn-tri-PcNc-4 with six diphenylphenoxy groups, while Zn-tri-PcNc-4 yielded a 3.22% efficiency in sensitizing TiO2-based solar cell, much higher than that (1.30%) of the S-substituted analog (Zn-tri-PcNc-5). The decreased efficiency of Zn-tri-PcNc-5 is due to the molecular orbital shift to negative direction, stemmed from S atoms instead of O atoms in the six substituents of Zn-tri-PcNc-4, which leads to insufficient driving force for the electron injection. The present results demonstrate that the optimization of molecular orbital levels of ZnPcs via changing the substituents’ “push–pull” effect is an effective approach to improve the ZnPc-sensitized cell performance.

An organic–inorganic rectifying contact based on a ZnPc derivative

An organic–inorganic rectifying contact was fabricated by forming a thin film of a Zinc Phthalocyanine (ZnPc) derivative, Zinc 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine (oc-ZnPc), on a p-Si wafer and evaporating Al on the structure. The current–voltage (I–V) and capacitance–voltage (C–V) measurements of Al/oc-ZnPc/p-Si structure were taken in dark at room temperature. The I–V measurements proved that the structure showed excellent rectification. Some basic diode parameters like ideality factor and barrier height were calculated from lnI–V plot. Ideality factor and barrier height values were found as 1.44 and 0.78eV, respectively. The series resistance value of the structure was determined as 5.46kΩ by means of Norde functions. The C–V measurements were taken for various frequencies and it was seen that the capacitance value decreased with increasing frequency.In addition I–V measurements of the Al/oc-ZnPc/p-Si/Al were repeated under light which had illumination intensity of 40–100mW/cm2. It was observed that reverse bias current of the diode increased with the light intensity. Therefore, the structure showed photodiode characteristics and it can be used for electrical and optoelectronic applications.

Effect of pyrene substitution on the formation and sensor properties of phthalocyanine-single walled carbon nanotube hybrids

The hybrids of single walled carbon nanotubes (SWCNTs) with symmetrically octasubstituted zinc phthalocyanine (2) bearing eight polyoxyethylene groups and asymmetrically substituted zinc phthalocyanine (1) bearing one pyrene and six polyoxyethylene groups as side chains have been prepared and characterized by Raman and fluorescence emission spectroscopies, scanning electron and transmission electron (SEM and TEM) microscopies, and thermogravimetric analysis. The pyrene group was chosen to enhance the interaction of phthalocyanine molecules with SWCNTs. Thin films of pristine SWCNTs and SWCNT/ZnPc hybrids were prepared by drop casting onto interdigitated electrodes and employed as active layers to detect ammonia vapour (1–200ppm) by measuring electrical resistance changes. A comparative analysis of sensors’ response of pristine SWCNTs and SWCNT/ZnPc hybrid films to ammonia vapour was carried out to demonstrate the synergic effect between SWCNTs and ZnPc derivatives. Influence of pyrene substituent in the phthalocyanine ring on the hybrid formation and their sensor response has also been discussed.

Characterization of Langmuir and Langmuir–Blodgett films of an octasubstituted zinc phthalocyanine

In this work we report the fabrication of Langmuir and Langmuir–Blodgett (LB) films of a substituted ZnPc (octakis(oxyoctyl)phthalocyanine of zinc), and their characterization by means of several techniques. These characterization techniques include surface pressure (π-A) and surface potential (ΔV-A) isotherms as well as UV–vis Reflection spectroscopy and Brewster Angle Microscopy (BAM) for the films at the air–water interface together with UV–vis absorption and IR spectroscopies and Atomic Force Microscopy (AFM) for the LB films. The π-A and ΔV-A isotherms and BAM images indicate a phase transition at a surface pressure of ca. 9mN/m and a multilayer formation at surface pressures around 19–20mN/m; at a surface pressure around 27mN/m a disordered collapse of the film occurs. In addition, AFM images of LB films at π=10mN/m and π=20mN/m show a monomolecular and a multilayered film, respectively. The comparison of the UV–vis spectrum of ZnPc in solution, the reflection spectra of the Langmuir films and UV–vis spectra of LB films reveals a significant reduction in the Q band intensity for the films, indicative of an organization of ZnPc in the Langmuir and LB films versus the random distribution in solution. The UV–vis Reflection spectra are also consistent with multilayer formation at surface pressures around 19–20mN/m. The relative intensities of the IR spectrum bands change from the KBr pellet to the LB film which is also attributable to orientation effects in the film. Cyclic voltammetric experiments of LB films incorporating the ZnPc derivative show peaks that can be correlated with redox processes occurring in the phthalocyanine ring. A small but significant influence of the surface pressure and the number of deposited layers in the electrochemical behaviour is observed. The electrochemical response of cast films exhibits some differences with respect to that of LB films which have been attributed to their different molecular organizations.

Zn-phthalocyanine-functionalized nanometal and nanometal-TiO₂ hybrids: aggregation behavior and excited-state dynamics.

Dithiol-substituted Zn-phthalocyanine derivatives (TAZnPc1, TAZnPc2 and TAZnPc3) were synthesized and functionalized on nanometals (Au and Ag) and nanometal-TiO2 hybrids were harnessed to cover the visible region of the absorption spectrum. Photophysical studies reveal that both H- and J-aggregation were present in the ZnPc-functionalized nanometal, and the extent of J-aggregation is superior on the surface of Ag nanoparticles. On the other hand, no H-aggregation was observed in the nanometal-TiO2 hybrid film, despite the fact that the tetra-anchoring derivative (TAZnPc3) shows lesser J-aggregation on the nanometal-TiO2 hybrid film than that of other two mono-anchoring derivatives (TAZnPc1 and TAZnPc2). Further, the electron injection and recombination processes were investigated by time-resolved fluorescence and absorption spectroscopy. All the derivatives furnish biexponential decay on the nanometal surface. The shorter component is due to electron injection of ZnPc-nanometal particles and the longer component is due to free ZnPc. The rate of electron injection is faster for ZnPc-gold nanoparticles than that of silver nanoparticles, predominantly in TAZnPc1. This is due to the greater aggregation tendency of ZnPc derivatives on Ag nanoparticles than Au nanoparticles. After electron injection, the electron-transfer product (i.e. the radical cation of ZnPc) was observed at 600 nm. Moreover, the fluorescence of ZnPc derivatives on nanometal-TiO2 films was completely quenched due to the shuttling of electrons from ZnPc to TiO2 efficiently by metal nanoparticles.