Donor−Acceptor Phthalocyanine Nanoaggregates

Supramolecular organization of phthalocyanines: from solution to surface

Phthalocyanines are an interesting class of aromatic macrocycles which possess exciting electrical, redox and photophysical properties that make them ideal building blocks for applications in different technological fields. However, the incorporation of phthalocyanines into devices is often tied to the possibility of organizing these macrocycles into arrays using supramolecular interactions. To date, several supramolecular motifs such as hydrogen-bonding, donor-acceptor or metal-ligand interactions have been used to promote the phthalocyanines' organization in solution. Furthermore, such weak, non-covalent interactions have also been widely employed to foster the organization of these macrocycles in condensed phases such as liquid-crystals or thin films. This micro-review provides a brief overview of the contribution made by some research groups in Spain towards the preparation of organized phthalocyanine-based supramolecular systems.

Recent developments in the synthesis of homo- and heteroarrays of porphyrins and phthalocyanines

Here, we report the progress in the chemistry of porphyrin-phthalocyanine and phthalocyanine-phthalocyanie multinuclear systems being developed by the organic chemistry groups of Cavaleiro and Torres.

[2,2]paracyclophane-bisphthalocyanines: non-classical push-pull systems for second harmonic generation

The EFISH and HRS responses of a push-pull bisphthalocyanine-[2,2]paracyclophane compound have been measured at 1.9 and 1.06 μm, respectively, obtaining a remarkably high hyperpolarizability β HRS value. Since the two electronically different phthalocyanine chromophores are connected through a non π-conjugated and rigid [2,2]paracyclophane spacer, this result implies an efficient through-space intramolecular charge transfer between them. The results have been compared to that of structurally related, unsymmetrically substituted phthalocyanines 2-5, bearing either [2,2]paracyclophane or phenyl substituents. In these cases, the [2,2]paracycloplane does not play a significant role in the NLO response, being that the nature of the peripheral sustituents on the phthalocyanine is the most influent structural feature.

Light harvesting phthalocyanine/subphthalocyanine system: intermolecular electron-transfer and energy-transfer reactions via the triplet subphthalocyanine

Photoinduced electron transfer from the electron-donating zinc tetra-tert-butylphthalocyanine, ZnTBPc , to the electron-accepting dodecafluorosubphthalocyanine, SubPcF12 , in the polar benzonitrile has been investigated with nanosecond laser photolysis method. The examined ZnTBPc/SubPcF12 mixture absorbs the light in a wide section of the UV/vis/NIR spectra. Owing to the particular electronic properties of both entities, such combination seems to be perfectly suited for the study of intermolecular electron-transfer process in the polar solvents via the triplet-excited state of SubPcF12 . Upon excitation of SubPcF12 with 570 nm laser light in polar benzonitrile (εs = 25.2), the electron transfer from ZnTBPc to the triplet-excited state of SubPcF12 was confirmed by observing the transient absorption bands of ZnTBPc radical cation and SubPcF12 radical anion in the visible and near-IR region. On addition of an appropriate electron acceptor with excellent electron-accepting properties, namely dicyanoperylene-3,4,9,10-bis(dicarboximide) ( PDICN2 ), the anion radical of SubPcF12 transfers to the PDICN2 yielding the PDICN2 radical anion. These observations confirm the photosensitized electron-transfer/electron-mediating cycle of ZnTBPc/SubPcF12/PDICN2 system. In non-polar toluene (εs = 2.2), the energy-transfer process from the triplet-excited state of SubPcF12 to the low-lying triplet state of ZnTBPc was confirmed by the consecutive appearance of the triplet ZnTBPc .

Synthesis of all-cis and all-trans tetrakis(phenylvinylene)-phthalocyanines

We have synthesized a series of tetrakis(arylvinylene)phthalocyanines from the corresponding phthalonitriles. Substitution of the para-fluorine in the pentafluorphenyl ring with an alkoxy group from the solvent occurs during the synthesis. This substitution can be suppressed by the addition of zinc chloride or tin chloride to the reaction mixture. According to 1 H and 19 F NMR data, the cis- or trans-conformations of the starting materials are retained during condensation; thus the phthalocyanines formed are in all-cis or all-trans form. Cis-trans photoisomerization occurs easily for phthalonitriles, while phthalocyanines retain their conformations under UV beam.

Phthalocyanine-phthalocyanine salt crystal: a unique assembly design

A unique salt composed of cationic and anionic phthalocyanine complexes has been prepared and structurally characterized. The cationic component is di(pyridine)(phthalocyaninato)cobalt(III) and the anionic one is dicyano(phthalocyaninato)cobalt(III). They arrange alternately in the crystal, forming a two-dimensional sheet with partial π–π overlaps.

Photophysical and theoretical insights on non-covalently linked fullerene-zinc phthalocyanine complexes

The photo-physical aspects of non-covalently linked assemblies of a series of fullerenes, namely, C60, C70, tert-butyl-(1,2-methanofullerene)-61-carboxylate (1) and [6,6]-phenyl C70 butyric acid methyl ester (2) with a designed zinc phthalocyanine (ZnPc), viz., zinc-1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine (3) in toluene medium are studied employing absorption spectrophotometric, steady state and time resolved fluorescence spectroscopic measurements. Of central interest in these investigations is the preferential binding of various fullerenes with ZnPc in toluene. The ground state interaction between fullerenes and 3 is first evidenced from UV-Vis measurements. Steady state fluorescence experiment reveals efficient quenching of the excited singlet state of 3 in presence of both underivatized and derivatized fullerenes. K values for the complexes of C60, C70, 1 and 2 with 3 are determined to be 6500, 22,230, 47,800 and 54,770 dm3 mol(-1), respectively. The magnitude of K suggests that 3 preferentially binds C70 and derivatized C70 in comparison to C60 and 1. Time resolved emission measurements establish that C(70)-3 and 2-3 complexes are stabilized much more in comparison to C(60)-3 and 1-3 systems in terms of charge separation process. Semi empirical calculations employing third parametric method substantiate the strong binding of C70 and its derivative with 3 in terms of heat of formation values of the respective complexes, and at the same time, determine the orientation of bound guest (here fullerenes) with the molecular plane of 3.

Photocontrollable J-aggregation of a diarylethene-phthalocyanine hybrid and its aggregation-stabilized photochromic behavior

The photocontrollable J-aggregation of a diarylethene-phthalocyanine hybrid (T-ZnPc) and its aggregation-stabilized photochromic behavior were investigated by various techniques. T-ZnPc initially exhibited slight J-aggregation tendency in solvents such as chloroform and toluene through conformational planarization effect, but formed much stronger J-aggregates upon the illumination of 254 nm UV light. In darkness, the UV-irradiated solutions gradually returned to their initial state. These phenomena can be explained by the pronounced change in molecular planarity accompanying the reversible isomerization of the diarylethene units of T-ZnPc. Besides, we have found that the thermal stability of the closed-ring diarylethene isomers in molecularly dispersed T-ZnPc is much poorer than that in aggregates. As long as the aggregates were broken, they converted to corresponding open-ring form instantly. This study provided an example of fully photocontrollable aggregation of phthalocyanines and paved a new way for improving the stability of the photochromic systems.

Phthalocyanine-Carbon Nanostructure Materials Assembled through Supramolecular Interactions

The use of self-assembly for the construction of materials based on phthalocyanines and carbon nanostructures-fullerenes, single-walled carbon nanotubes, and graphene-has demonstrated to be a versatile strategy for the preparation of novel, multifunctional systems. Photophysical studies carried out on these photo- and electroactive supramolecular ensembles have revealed the occurrence of an efficient photoinduced electron-transfer process, thus paving the way for the utilization of these materials as active components in optoelectronic devices. This Perspective highlights the recent progress in the preparation of such materials and the potential use of these systems for the construction of nanostructured materials with singular physicochemical properties.

Electrochemical and in situ Spectroelectrochemical Properties of Phthalocyanines Bearing N-Benzyl-4-Phenyloxyacetamide Moieties

The general redox behaviour of phthalocyanines bearing N-benzyl-4-phenyloxyacetamide moieties (H2Pc, ZnPc, NiPc, CuPc, and CoPc) has been identified by cyclic voltammetry and differential pulse voltammetry on Pt in dimethylsulfoxide/tetrabutylammonium perchlorate. These measurements showed that the complexes indicate subsequent one-electron reduction and oxidation processes. Although the voltammetric measurements implied the association of the redox processes of some complexes with aggregation phenomenon, the complete evaluation of the aggregation effects by only these measurements was not possible. In situ UV-Vis spectroelectrochemical measurements enabled us to assign the ligand- and metal-based redox processes, and identify if the aggregation affects these processes. These measurements suggested that the redox processes of H2Pc, NiPc, and CuPc are coupled by aggregation phenomenon, while those of ZnPc and especially CoPc are not, probably due to the difference in their axial coordinating properties.

Helical nanostructures self-assembled from optically active phthalocyanine derivatives bearing four optically active binaphthyl moieties: effect of metal-ligand coordination on the morphology, dimension, and helical pitch of self-assembled nanostructures

(R)- and (S)-enantiomers of optically active metal free tetrakis[11,12:13,14-di(1',2'-naphtho)-1,4,7,10,15,18-hexaoxacycloeicosa-2,11,13-trieno]-phthalocyanine and their zinc complexes, (R)- and (S)-H(2)Pc (1) and (R)- and (S)-ZnPc (2), were prepared from the tetramerization of corresponding phthalonitriles, (R)- and (S)-2,3-(4',5'-dicyanobenzo)-11,12:13,14-di(1',2'-naphtho)-1,4,7,10,15,18-hexaoxacycloeicosa-2,11,13-triene, in the absence and presence of Zn(OAc)(2).2H(2)O template, respectively, promoted by organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Their self-assembly behavior in the absence and presence of 4,4'-bipyridine has been comparatively investigated by electronic absorption and circular dichroism (CD) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) technique, and X-ray photoelectron spectroscopy (XPS). The metal free phthalocyanine self-assembles into highly ordered fibrous nanostructures (ca. 3 microm length, 70 nm width, and 125 nm helical pitch) with left-handed and right-handed helicity for (R)-1 and (S)-1, respectively, through the hierarchical manner via one-dimensional helices with chirality determined by the optically active binaphthyl side chains. In contrast, self-assembly of the phthalocyaninato zinc analogue leads to the formation of nanoparticles. However, in the presence of 4,4'-bipyridine, additionally formed metal-ligand Zn-N(4,4'-bipyridine) coordination bonds between the nitrogen atoms of additive 4,4'-bipyridine molecule and the zinc center of (R)- and (S)-2 molecules together with pi-pi interaction and chiral discrimination of chiral side chains induce a right-handed and left-handed helical arrangement in a stack of (R)- and (S)-2 molecules, respectively, which further hierarchically packs into highly ordered fibrous nanostructures of average tens of micrometers in length, 30 nm width, and 106 nm helical pitch with the same helicity to the stack, revealing the effect of metal-ligand coordination bonding interaction on the morphology, dimension, handedness, and helical pitch of self-assembled nanostructures.

A bis(C60)-bis(phthalocyanine) nanoconjugate: synthesis and photoinduced charge transfer

A novel dimeric phthalocyanine-C60 nanoconjugate, consisting of a bisphthalocyanine core to which two fullerenes are attached, has been prepared. The synthetic strategy implemented the preparation of a diformyl butadiynyl-bridged bisphthalocynaninato-zinc(II) complex by means of palladium-catalyzed cross-coupling reactions and subsequent dipolar cycloaddition reactions. Photophysical experiments confirm that an intramolecular electron transfer, namely, from the photoexcited ZnPc moiety to the electron-accepting C60 unit, governs the overall photoreactivity of the nanoconjugate. Through-space charge-transfer interactions facilitated by the close proximity of the ZnPc and the C60 moieties play a decisive role in determining the lifetimes of the charge-separated state which range from 10(-10) to 10(-9) seconds.