The Synthesis and Physical Properties of Some Organo- and Organosiloxysilicon Phthalocyanines

Silicon phthalocyanines: synthesis and resurgent applications

Their unique axial bonds and NIR optical properties have made silicon phthalocyanines (SiPcs) valuable compounds. Herein, we present key synthetic strategies and emerging applications of SiPcs over the past decade.

Structural Data Showing the Existence of LDI Bonds between the Rings of Dimeric Cofacial Siloxysilicon Phthalocyanines

In a pair of earlier papers, the existence of long directional interaction bonds, LDI bonds, was postulated on the basis of data for cofacial oligomeric siloxysilicon phthalocyanines from this laboratory and data for other cofacial oligomeric phthalocyanines from the literature. However, the combined data are not fully suited to the purpose for which they were used. Here an alternative approach is taken in which a carefully chosen group of dimeric cofacial siloxysilicon phthalocyanines is used. Structural data derived from these phthalocyanines is examined in some detail to determine where it conforms to normal expectations and where it does not. To a high degree of certainty, consideration of the results obtained shows that long directional (LDI) bonds exist in dimeric cofacial siloxysilicon phthalocyanines. The new data also provide an opportunity for other research on chemical bonds.

Synthesis, properties and drug potential of the photosensitive alkyl- and alkylsiloxy-ligated silicon phthalocyanine Pc 227

Photolysis of Pc 227 yields the extensively studied photodynamic therapy drug Pc 4. The photolytic pathway is a homolysis involving a phthalocyanine π radical and low bond dissociation energy.

Some reactions of phthalocyanines of silicon, germanium and tin under alkaline conditions

Phthalocyaninatosilicon(IV), germanium(IV) and tin(IV) dihydroxides react with potassium hydroxide in o-xylene in the presence of crown ether 15-cr-5 initially forming paramagnetic compounds of dark-blue color with absorption bands at 580–590 nm and 620–625 nm and then diamagnetic compounds of red color with an absorption band at 518–523 nm. The red compounds are very reactive towards proton donors, restoring the initial phthalocyanines, and oxidation agents under decomposition of the phthalocyanines. The color changes are due to the formation of the mono- and dianions, ( PcMO 2)2- and ( PcMO 2)-, accompanied with transfer of electrons from oxygen atoms to the tetrapyrrol macrocycle.

Synthesis and some spectroscopic properties of tetra-2,3-pyridoporphyrazinatosilicon involving bulky axial ligands

Tetra-2,3-pyridoporphyrazinatosilicon ( SiPyD ) containing bis(tri-n-hexylsiloxy) (1) or bis(n-heptylcarbonyloxy) (2) axial ligands have been prepared and characterized by NMR, IR and electronic absorption spectroscopies and by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). These SiPyDs are soluble in common organic solvents, and face-to-face-type stacking is prevented in solution and films. Accordingly, their NMR spectra could be reasonably assigned. Their electronic absorption spectra in solution appear to the blue and red compared with those of the corresponding Si phthalocyanines ( SiPcs ) and Si tetrapyrazinoporphyrazines ( SiPyZs ) respectively. These characteristics are reproduced by molecular orbital calculations in the framework of the Pariser-Parr-Pople approximation. On formation of films, the Q bands shift to the red of those in solution by ca 20 nm, suggesting that other similar tetravalent metallophthalocyanines with two long axial ligands can be used for shifting the Q band to the red. TGA and DTA experiments show that the thermal stability of the macrocycles is markedly influenced by the type of axial ligands.

Synthesis of Acetylene Bridged Germanium Phthalocyanines

The octaalkyl- or octaalkoxysubstituted phthalocyaninatogermanium dichlorides 10b,d,e and 10a-c were reacted with bisbromomagnesiumacetylene 16 and bisbromomagnesium- p-diethynylbenzene 18, respectively with formation of the corresponding acetylene bridged oligomers 17a-c and 19a-c, respectively.

Unmasking the chemistry and properties of non-peripherally octasubstituted phthalocyanines

The paper reviews the development of the chemistry, properties and applications of 1,4,8,11,15,18,22,25- (or non-peripheral) octasubstituted phthalocyanines that has been undertaken at the University of East Anglia over the last quarter of a century. The research has proved valuable for initiating and developing a number of areas of phthalocyanine science, not least because the compounds exhibit a number of properties seldom shared by Pc derivatives with other substitution patterns. In particular the compounds are obtained isomerically pure and the substituents' location at the non-peripheral sites as opposed to the peripheral positions ensures superior solubility and lower aggregation in most hydrophobic solvents. A further significant difference between isomeric non-peripheral (np)- and peripheral (p)-octasubstituted compounds is the effect of substituents on the energy of the Q-band, those at the former positions leading to more significant bathochromic shifts of this absorption band into the near infra-red. Examples of np-octasubstituted derivatives exhibit columnar mesophase behavior, a property shared by their p-octasubstituted counterparts. The favorable solubility of the np-octasubstituted compounds, including examples in which one of the four benzenoid rings bears different substituents from those on the other three (so called AAAB structures), in organic solvents facilitates their deposition as thin film formulations. A high degree of molecular organisation within Langmuir-Blodgett (LB) films of amphiphilic AAAB compounds has been investigated using various methods. Spin-coated films of certain AAAA and AAAB series of compounds have been shown to contain layer structuring and purpose designed AAAB compounds have been used in formation of self-assembled monolayers (SAMs). The use of LB and spin-coated films within electrical devices is described. Various applications of SAMs deposited on gold surfaces have been explored including gas sensing. Recent attention has focused on their use, when deposited onto gold nanoparticles, for applications in PDT, an approach complementing more conventional PDT studies. The principal challenge for obtaining the np-octasubstituted compounds is in preparing the precursor phthalonitriles. Though 3,6-dialkoxyphthalonitriles are readily prepared, early access to the 3,6-dialkylphthalonitriles was somewhat laborious. However, more convenient syntheses of the latter are now available through metal catalyzed cross-coupling reactions. Interesting contrasts in the reactivity of 3,6-dialkylphthalonitriles and 4,5-dialkylphthalonitriles have been uncovered. Thus reactions of the former with excess lithium in alcoholic solvents or with excess MeMgBr provide particularly ready access to examples of macrocycles that are hybrids of the Pc and tetrabenzoporphyrin structures. This level of reactivity is very different among the 4,5-dialkylphthalonitriles. Unexpectedly limited reactivity of np-octahexylsubstituted Si(OH)2Pc in condensation reactions has been exploited to provide a basis for the stepwise construction of m-oxo linked hetero-chromophore arrays. Finally, the unexpected construction of the novel EPR active Cd2Pc3 complexes from both np- and p-octaalkyl substituted CdPcs provided examples where both series behaved similarly – in contrast to behavior exhibited by alternatively substituted CdPcs investigated to date.

Stepwise syntheses of complex μ-oxo-linked heterochromophore arrays containing phthalocyanine, porphyrin and subphthalocyanine ligands

The article reviews the exploitation of the serendipitous discovery that dihydroxysilicon 1,4,8,11,15,18,22,25-octakis(hexyl)phthalocyanine 1 reacts at one face only to form a μ-oxo linked bond to dichlorosilicon phthalocyanine. Reaction of 1 with dihydroxysilicon octaethylporphyrin led to an unstable μ-oxo linked Pc-O-Pn heteroligand dyad that could not be isolated. However, reaction with dihydroxygermanium octaethylporphyrin gave a stable dyad that showed substantial broad band absorption attributable to exciton effects. A small amount of the μ-oxo linked homo dyad formed by self-condensation of dihydroxygermanium octaethylporphyrin was detected by MALDI-TOF mass spectrometry but was not isolated. Reaction of 1 with chloroboron subphthalocyanine afforded the stable Pc-O-SubPc heterodyad as the main product and the SubPc-O-Pc-O-SubPc triad as a minor side product. Both gave absorption spectra that showed the main features of the ligands present, implying limited exciton coupling. A further reaction of 1 with axial-hydroxy, axial-methyl silicon phthalocyanine provided a key Pc-O-Pc′ dyad that proved to be an ideal intermediate for developing a synthetic strategy to access a series of hetero-metalloid/hetero-ligand Pc-O-Pc′-O-Pn triads. X-ray structural data for examples of these arrays are discussed. A feature of the triad compounds is their very broad band absorption spectra that extends from the UV through the visible region to near IR wavelengths.

Long, directional interactions in cofacial silicon phthalocyanine oligomers

Single crystal structures have been determined for the three cofacial, oxygen-bridged, silicon phthalocyanine oligomers, [((CH(3))(3)SiO)(2)(CH(3))SiO](SiPcO)(2-4)[Si(CH(3))(OSi(CH(3))(3))(2)], and for the corresponding monomer. The data for the oligomers give structural parameters for a matching set of three cofacial, oxygen-bridged silicon phthalocyanine oligomers for the first time. The staggering angles between the six adjacent cofacial ring pairs in the three oligomers are not in a random distribution nor in a cluster at the intuitively expected angle of 45° but rather are in two clusters, one at an angle of 15° and the other at an angle of 41°. These two clusters lead to the conclusion that long, directional interactions (LDI) exist between the adjacent ring pairs. An understanding of these interactions is provided by atoms-in-molecules (AIM) and reduced-density-gradient (RDG) studies. A survey of the staggering angles in other single-atom-bridged, cofacial phthalocyanine oligomers provides further evidence for the existence of LDI between cofacial phthalocyanine ring pairs in single-atom-bridged phthalocyanine oligomers.

Structure-activity and mechanism studies on silicon phthalocyanines with Plasmodium falciparum in the dark and under red light

Syntheses for the new photosensitizers HOSiPcOSi(CH3)2(CH2)3N(CH1)1 or 3(CH3)2, Pc 34 and Pc 25, have been developed and the order of activity of these photosensitizers and the previously reported photosensitizer Pc 4, HOSiPcOSi(CH3)2(CH2)3N(CH3)2, in the dark and with broad-band red light toward Plasmodium falciparum in red blood cell (RBC) suspensions has been studied. The order of activity has been found to be Pc 4 > Pc 34 > Pc 25. Thus, the activity of the photosensitizers under both sets of conditions is inversely proportional to the length of their terminal amino alkyl chains. The 50% inhibition dye concentration (IC50) in the dark for the parasites in RBC suspension with Pc 4 is 24 nM and the dye concentration and light fluence that yield > or = 3 log10 of parasite inactivation with Pc 4 are 2 microM and 3 J/cm2, respectively. The synthesis of DNA and proteins by the parasites in culture was strongly inhibited by Pc 4 in the dark while parasite lactate dehydrogenase (pLDH) activity was unaffected. With Pc 4 and light, DNA and protein synthesis of the parasites in culture was strongly inhibited, pLDH activity of the parasites was moderately inhibited and ribosome density of the parasite cells was reduced. Gel electrophoresis studies showed that synthesis of all parasite proteins was inhibited to a similar extent. These results suggest that Pc 4 both in the dark and with light inactivates the cells by disturbing their machinery for the synthesis of not just one but a whole series of proteins. It is concluded that Pc 4 and light may be able to serve as a practical sterilization combination not only for HIV and other viruses but also for malaria parasites in RBC concentrates, and that Pc 4 by itself may have potential as a chemotherapeutic agent toward malaria.

New phthalocyanine photosensitizers for photodynamic therapy

Six new aluminum and silicon phthalocyanines have been synthesized and their photocytotoxicity toward V79 cells has been studied. The compounds that have been prepared are: A1PcOSi(CH3)2(CH2)3N(CH3)2, I; A1Pc-OSi(CH3)2(CH2)3N(CH3)3+I-, II; CH3SiPcOSi(CH3)2(CH2)3N(CH3)2, III; HOSiPcOSi(CH3)2(CH2)3N(CH3)2, IV; HOSiPcOSi(CH3)2(CH2)3N(CH3)3+I-, V; and SiPc[OSi(CH3)2(CH2)3N(CH3)3+I-]2, VI. Relative growth delay values for compounds I-VI and relative cytotoxicity values for compounds I, II, IV, V and VI have been determined. Compounds I and II have been shown to be comparable in photocytotoxicity to what is presumed to be A1PcOH.xH2O, and compound IV has been shown to have greater activity. The classes of compounds to which these six compounds belong appear to have potential for photodynamic therapy.