Study of Substituent Effects on the Photoconductivity of Soluble 2,(3)- and 1,(4)-Substituted Phthalocyaninato- and Naphthalocyaninatotitanium(IV) Oxides

Investigation of the photoconductive properties of thiophene substituted metallo-phthalocyanines

The synthesis of 4-(thiophen-3-ylethynyl)phthalonitrile was achieved via the Sonogashira cross-coupling reaction. Herein, we report the synthesis of symmetrical metallo-phthalocyanines with cobalt, zinc, and manganese as the metal ions, and tetrakis(ethynylthiophene) groups substituted at the peripheral positions. The new compounds have been characterized by using mass, ¹H NMR, ¹³C NMR, FT-IR and UV-vis spectroscopy. Dark and photoconductivity measurements were carried out on spin coated thiophene substituted metallo-phthalocyanines at various temperatures fixed between 300 and 440 K. Photocurrent generation and charge transport mechanisms are discussed as well. The evaluation of the photoconductive properties of these compounds indicated that the photocurrent generation efficiency and charge transport mechanism exhibited a strong temperature dependence. On the other hand, conductivity measurements revealed that the temperature dependence of the conductivity can be described by the Arrhenius type exponential equation under dark conditions. Furthermore, it was found that the photoconductive behavior of the film can be described successfully by the variable range hopping model for the whole investigated temperature range.

Molecular Design Strategy in Developing Titanyl Phthalocyanines as Dopant-Free Hole-Transporting Materials for Perovskite Solar Cells: Peripheral or Nonperipheral Substituents?

We demonstrate a molecular design strategy to enhance the efficiency of phthalocyanine (Pc)-based hole-transporting materials (HTMs) in perovskite solar cells (PSCs). Herein, two titanyl phthalocyanine (TiOPc) derivatives are designed and applied as dopant-free HTMs in planar n-i-p-structured PSCs. The newly developed TiOPc compounds possess eight n-hexylthio groups attached to either peripheral (P-SC₆-TiOPc) or nonperipheral (NP-SC₆-TiOPc) positions of the Pc ring. Utilizing these dopant-free HTMs in PSCs with a mixed cation perovskite as the light-absorbing material and tin oxide (SnO₂) as the electron-transporting material (ETM) results in a considerably enhanced efficiency for NP-SC₆-TiOPc-based devices compared to PSCs using P-SC₆-TiOPc. Hence, all of the photovoltaic parameters, including power conversion efficiency (PCE), fill factor, open-circuit voltage, and short-circuit current density, are remarkably improved from 5.33 ± 1.01%, 33.34 ± 3.45%, 0.92 ± 0.18 V, and 17.33 ± 2.08 mA cm^-2 to 15.83 ± 0.44%, 69.03 ± 1.59%, 1.05 ± 0.01 V, and 21.80 ± 0.36 mA cm^-2, respectively, when using the nonperipheral-substituted TiOPc derivative as the HTM in a PSC. Experimental and computational analysis suggests more compact molecular packing for NP-SC₆-TiOPc than P-SC₆-TiOPc in the solid state due to stronger π-π interactions, leading to thin films with better quality and higher performance in hole extraction and transportation. PSCs with NP-SC₆-TiOPc also offer much higher long-term stability than P-SC₆-TiOPc-based devices under ambient conditions with a relative humidity of 75%.

Super-Sensitive Protonation Behavior of Trifluoroethoxy-Substituted Phthalocyanines and Their Application to Solvent Discrimination

The super-sensitive protonation behavior of trifluoroethoxy-substituted phthalocyanines (TFEO-Pcs) was carefully studied using UV-vis and fluorescence spectroscopy, as well as computational calculations. The practical utility of TFEO-Pcs in sensor technology was demonstrated by identifying chloroform samples from different commercial sources.

Synthesis and application of trifluoroethoxy-substituted phthalocyanines and subphthalocyanines

Phthalocyanines and subphthalocyanines are attracting attention as functional dyes that are applicable to organic solar cells, photodynamic therapy, organic electronic devices, and other applications. However, phthalocyanines are generally difficult to handle due to their strong ability to aggregate, so this property must be controlled for further applications of phthalocyanines. On the other hand, trifluoroethoxy-substituted phthalocyanines are known to suppress aggregation due to repulsion of the trifluoroethoxy group. Furthermore, the electronic characteristics of phthalocyanines are significantly changed by the strong electronegativity of fluorine. Therefore, it is expected that trifluoroethoxy-substituted phthalocyanines can be applied to new industrial fields. This review summarizes the synthesis and application of trifluoroethoxy-substituted phthalocyanine and subphthalocyanine derivatives.

Four Dibutylamino Substituents Are Better Than Eight in Modulating the Electronic Structure and Third-Order Nonlinear-Optical Properties of Phthalocyanines

2(3),9(10),16(17),23(24)-Tetrakis(dibutylamino)phthalocyanine compounds M{Pc[N(C4H9)2]4} (1-5; M = 2H, Mg, Ni, Cu, Zn) were prepared and characterized by a range of spectroscopic methods in addition to elemental analysis. Electrochemical and electronic absorption spectroscopic studies revealed the more effective conjugation of the nitrogen lone pair of electrons in the dibutylamino side chains with the central phthalocyanine π system in M{Pc[N(C4H9)2]4} than in M{Pc[N(C4H9)2]8}, which, in turn, results in superior third-order nonlinear-optical (NLO) properties of H2{Pc[N(C4H9)2]4} (1) over H2{Pc[N(C4H9)2]8}, as revealed by the obviously larger effective imaginary third-order molecular hyperpolarizability (Im{χ((3))}) of 6.5 × 10(-11) esu for the former species than for the latter one with a value of 3.4 × 10(-11) esu. This is well rationalized on the basis of both structural and theoretical calculation results. The present result seems to represent the first effort toward directly connecting the peripheral functional substituents, electronic structures, and NLO functionality together for phthalocyanine molecular materials, which will be helpful for the development of functional phthalocyanine materials via molecular design and synthesis even through only tuning of the peripheral functional groups.

Solution Processed Titanyl Phthalocyanines as Donors in Solar Cells: Photoresponse to 1000 nm

We report a route to thin-film polymorphs of soluble TiOPc derivatives that exhibit similar near-IR absorptivities as vapor deposited thin-films of the parent TiOPc chromophore (phase-I and phase-II polymorphs) and demonstrate that solution-processed planar and bulk heterojunction solar cells fabricated with one of these derivatives exhibited photoactivity throughout the same near-IR wavelength range without compromising VOC. Solution-processed thin-films of soluble octakis(alkylthio)-substituted TiOPc derivatives 1-3 exhibit absorption extending to 1000 nm. When incorporated into OPV devices, the contributions from the lowest CT excitonic state (QB band) of 1 to device performance were evident in both PHJ and BHJ architectures, indicating sufficient driving force for PIET. This contribution was improved via intimate mixing of donor and acceptor molecules in a BHJ architecture, albeit with a decrease in efficiency. IPCE of the best performing BHJ device revealed a contribution from 1 exceeding that of acceptor PCBM, and extending to 1000 nm.

Factors affecting the stability and performance of ionic liquid-based planar transient photodetectors

A novel planar architecture has been developed for the study of photodetectors utilizing the transient photocurrent response induced by a metal/insulator/semiconductor/metal (MISM) structured device, where the insulator is an ionic liquid (IL-MISM). Using vanadyl 2,3-naphthalocyanine, which absorbs in the communications-relevant near-infrared wavelength region (λ(max,film) ≈ 850 nm), in conjunction with C60 as a bulk heterojunction, the high capacitance of the formed electric double layers at the ionic liquid interfaces yields high charge separation efficiency within the semiconductor layer, and the minimal potential drop in the bulk ionic liquid allows the electrodes to be offset by distances of over 7 mm. Furthermore, the decrease in operational speed with increased electrode separation is beneficial for a clear modeling of the waveform of the photocurrent signal, free from the influence of measurement circuitry. Despite the use of a molecular semiconductor as the active layer in conjunction with a liquid insulating layer, devices with a stability of several days could be achieved, and the operational stability of such devices was shown to be dependent solely on the solubility of the active layer in the ionic liquid, even under atmospheric conditions. Furthermore, the greatly simplified device construction process, which does not rely on transparent electrode materials or direct electrode deposition, provides a highly reproducible platform for the study of the electronic processes within IL-MISM detectors that is largely free from architectural constraints.

Ti(IV) phthalocyanines for dye sensitized solar cells

Ti ( IV ) phthalocyanines axially coordinated to 2,3- and 1,8-naphthalenediols have been prepared and characterized. The naphthalene axial ligands have been endowed with none, one or two sulfonate anchoring groups in order to study the performance of the dyes as DSC photosensitizers. All studied compounds showed the same efficiency. The unexpected results suggest displacement of the axial ligand with concomitant formation of a di-μ-oxotitanium-type anchoring moiety between the hydroxylated TiO 2surface and the Ti -phthalocyanine. This is probably the reason why the type of axial ligand does not play any role on the overall device efficiency. The titanium phthalocyanine absorbed in this way shows state selective electron injection were only those photons absorbed by the Soret band are capable to inject electrons into the TiO 2, while photons absorbed by the Q-band result in negligible photocurrent. This fact could explain the low efficiency of the Ti -phthalocyanines.

Phthalocyanines as materials for advanced technologies: some examples

Metallophthalocyanine complexes and related compounds play an important role in many advanced applications and modern technologies mostly by virtue of their characteristic optical absorption and high chemical stability. As a class of materials made well-known by their vivid and fast colors, it is expected that metallophthalocyanines and analogues, e.g. naphthalocyanines, are going to keep their role with the increasing use of natural and artificial light in the technologies of the future. In the present review some relevant properties of phthalocyanines and related macrocycles for technological applications are analyzed. In particular the electrical conductivity and photoconductivity as well as some nonlinear optical properties (mostly optical limiting), of phthalocyanines and related compounds are discussed.

The renaissance in optical spectroscopy of phthalocyanines and other tetraazaporphyrins

Spectral properties of metallophthalocyanines and other tetraazaporphyrins are governed mainly by the Q band which originates from the π-π* transitions within the ring. The position and intensity of the Q band is important in tailoring new phthalocyanine derivatives for particular applications. Aggregation, the nature of the central metal, π conjugation, symmetry of the molecules, and axial, peripheral or non-peripheral substitutions affect the spectra and hence the properties of the phthalocyanine molecule. This review gives a brief outline on how optical spectroscopy provides useful informations on molecular and electronic structures, chemistry and physics of phthalocyanines and other tetraazaporphyrins.

Axially substituted titanium(IV) phthalocyanines

An easy synthesis of phthalocyaninatotitanium(IV) compounds substituted with bidentate ligands in the axial position is described. Using strongly chelating oxygen or sulfur donor ligands, the reaction of PcTiO with chelating agents leads to the formation of PcTiX complexes with X ≡ oxalate [Formula: see text], catecholate [Formula: see text], dithiocatecholate [Formula: see text], 2,3-dihydroxynaphthalene [Formula: see text] and other functionalized catechols (2c–2h). The new compounds possess an enhanced solubility in comparison to PcTiO .

Free-base tetra-arylphthalocyanines for dye-sensitised nanostructured solar cell applications

Adsorption of phthalocyanines lacking conventional attaching substituents onto nanostructured TiO 2 electrodes has been studied, and some of the important factors for sensitisation have been identified. Tetra-dimethoxyphenyl phthalocyanine (2) and tetra-phenyl phthalocyanine (3), derived from 4-(2,5-dimethoxyphenyl)phthalonitrile and 4-phenylphthalonitrile, respectively, are shown to successfully sensitise nanostructured TiO 2 electrodes, with IPCE max of 9 and 5% at λ = 650 nm . The dye-oxide systems have been characterised by UV-vis spectroscopy, cyclic voltammetry and photoelectrochemical methods, and the dye–surface interactions are discussed.

Fluorescence anisotropy and transient absorption of halogenated silicon(IV) phthalocyanines with axial poly(ethylene-glycol) substituents

Herein we report the utilization of fluorescence anisotropy to give rough hints on the conformation of three halogenated silicon-phthalocyanines with axially substituted polyethyleneglycol chains in solution. To deconvolute decay data sets from the instrumental response function a scanning fit algorithm was used, which facilitates the visualization of fitting accuracy and correlation of parameters of the assumed decay function. Moreover, to extend our investigation of photophysical properties in the nonlinear domain, the transient absorption in the picosecond range was measured and thus excited state absorption spectra are presented.

Synthesis and photochemical studies of substituted adjacent binaphthalophthalocyanines

Adjacent phthalocyanines with a binaphthalo backbone and phenoxy substituents were synthesized and their photochemical properties were investigated. The adjacent phthalocyanines are the binaphthalophthalocyanines, with the phenoxy, 4-tert-butylphenoxy and the sulfophenoxy substituents, respectively and bis-binaphthalophthalocyanine which has an extended π conjugation system and larger singlet oxygen quantum yield compared to the other compounds. The presence of the phenoxy substituents as well as the binaphthalo bridge does not cause a marked difference on the fluorescing properties of these complexes when compared to zinc phthalocyanine. The binaphthalo backbone allowed the molecules to photoswitch during photolysis affording them very high photostability.

2,3,9,10,16,17,24,25-Octakis(octyloxycarbonyl)phthalocyanines. Synthesis, Spectroscopic, and Electrochemical Characteristics

A series of three novel 2,3,9,10,16,17,24,25-octakis(octyloxycarbonyl)phthalocyanine compounds M[Pc(COOC8H17)8] (M = 2H, Cu, Zn) (1-3) have been synthesized via the cyclic tetramerization of 4,5-di(octyloxycarbonyl)phthalonitrile, which was obtained by a newly developed procedure with o-xylene as starting material, promoted with organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in the absence and presence of metal salt like M(acac)2.H2O (M = Cu, Zn) in n-octanol at 120 degrees C. In addition to elemental analysis, these novel octakis(octyloxycarbonyl)-substituted phthalocyanine compounds have been characterized by a series of spectroscopic methods. The electrochemistry of these compounds was also studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. A significant shift to the positive direction for both the first oxidation and the first reduction of compound 1, relative to H2Pc, reveals the electron-withdrawing nature of octyloxycarbonyl groups attached to the peripheral positions of phthalocyanine. The effect of peripheral octyloxycarbonyl substitution on the electrochemistry of the series of phthalocyanines 1-3 has been reasonably explained by theoretical calculation results using the density functional theory (DFT) method.

The Influence of Solvent Polarity and Metalation on Energy and Electron Transfer in Porphyrin−Phthalocyanine Heterotrimers

Heteroporphyrin and -phthalocyanine arrays represent an attractive class of light harvesters and charge-separation systems exhibiting an easy route of synthesis and high chemical stability. In the present work, we report the results of photophysical investigations of two novel non-sandwich-type porphyrin-phthalocyanine heterotriads, in which two meso-tetraphenylporphyrin rings (H2TPP or ZnTPP) are linked to the central silicon atom of a silicon(IV) phthalocyanine core. It was found that the photophysical properties of the triads (H2Tr and ZnTr) in N,N-dimethylformamide (DMF) and toluene are strongly affected by two different types of interaction between the porphyrin (P) and the phthalocyanine (Pc) parts, namely excitation energy transfer (EET) and photoinduced charge transfer. The first process results in appearance of the Pc fluorescence when the P-part is initially excited, and plays a dominant role in fast depopulation of the first excited singlet state of the P moiety. If the first excited singlet state of the Pc-part is populated (either directly or via EET), it undergoes fast depopulation by hole transfer (HT) to the charge-separated (CS) state. In polar DMF, the CS state is the lowest excited state, and the charge recombination occurs directly to the ground state. Using transient absorption spectroscopy, the lifetime of the CS state was estimated to be 30 and 20 ps for H2Tr and ZnTr, respectively. In nonpolar toluene, the energy gap between the first excited singlet state of the Pc-part and the CS state is very small, and back HT occurs in both triads, resulting in appearance of "delayed fluorescence" of the Pc-part with a decay time similar to the lifetime of the CS state (190 and 280 ps for H2Tr and ZnTr, respectively). Since the energy of the CS state of ZnTr in toluene is lower than that of H2Tr, the probability of back HT for ZnTr is lower. This was clearly proved by decay-associated fluorescence spectral measurements.

Synthesis, DFT calculations, linear and nonlinear optical properties of binuclear phthalocyanine gallium chloride

The axially substituted binuclear GaCl/GaCl phthalocyanine 1 with an unsymmetrical pattern of substitution has been prepared and its nonlinear optical (NLO) properties determined. The resulting binuclear complex retains approximately the same transition energies of monomeric (RO)8PcGaCl as far as the linear optical spectrum is concerned, although 1 has a double concentration of central atoms per molecule and an enlarged conjugated ligand. The lack of significant spectral shifts in passing from mononuclear to binuclear complexes has been rationalized theoretically by means of density functional theory calculations. The purpose of the present study is to determine whether binuclearity affects the optical limiting behavior of 1 with respect to monomeric (RO)8PcGaCl in the NLO regime determined by nanosecond laser pulses.

Recognition of Chiral Catechols Using Oxo−Titanium Phthalocyanine

Oxo-titanium phthalocyanine (TiOPc) derivatives of catechin and hematoxylin (natural ortho-diol type chiral compounds) have been prepared and characterized by spectral and chromatographic techniques. It is demonstrated that the TiOPc unit is an excellent template for chiral recognition through its isolated Q-transitions. The formation of a helical dimeric complex with hematoxylin induces strong CD-activity in the Q-band region. Ab initio geometry optimizations were combined with a Kuhn-Kirkwood coupled-oscillator mechanism to obtain the absolute configuration of hematoxylin. In addition, it is shown that the described chiroptical recognition method is sensitive to slight conformational changes.

Synthesis and characterization of (octaaryltetraazaporphyrinato)indium(III) complexes for optical limiting

The preparation of (octaaryltetraazaporphyrinato)indium(III) chlorides [aryl = phenyl (5a), p-tert-butylphenyl (6a), p-(trifluoromethyl)phenyl (7a), m-(trifluoromethyl)phenyl (8a)] and their reactions with aryl Grignard reagents XMgBr to give 5b-8b [X = p-(trifluoromethyl)phenyl] and 5c (R = 3,5-difluorophenyl) are described. The characterization of all compounds by UV-vis, FT-IR, and (1)H and (13)C NMR spectroscopy was performed. The hypsochromic shift of all bands in the absorption spectra of complexes 5a-8a is observed in the sequence 6a < 5a < 7a approximately 8a. This is associated with the increasing electron-withdrawing character of the aryl substituents in the periphery of the tetraazaporphyrin macrocycle. Compounds 8a,b are very good soluble in organic solvents with 8a exhibiting the higher photochemical stability among the various synthesized species. The optical limiting (OL) properties of the complexes have been studied and correlated with the structure of the (tetraazaporphyrinato)indium(III) complexes and the electronic nature of the different substituents. In particular, the OL effect at 532 nm increases on going from the series of compounds 5 to the series 8.