Tuning Photochemical and Photophysical Properties of P(V) Phthalocyanines

The ability of P(V) phthalocyanines (Pcs) for efficient singlet oxygen (SO) generation was demonstrated for the first time by the example of unsubstituted and α- and β-octabutoxy-substituted P(V)Pcs with hydroxy, methoxy and phenoxy ligands in the apical positions of the octahedral P centre. Variation of substituents in Pc ring and P(V) axial ligands allows careful tuning of photophysical and photochemical properties. Indeed, a combination of BuO groups in the β-positions of the Pc ring and PhO groups as axial ligands provides significant SO generation quantum yields up to 90%; meanwhile, the values of SO generation quantum yields for others investigated compounds vary from 27 to 55%. All the complexes, except α-substituted P(V)Pc, demonstrate fluorescence with moderate quantum yields (10-16%). The introduction of electron-donating butoxy groups, especially in the α-position, increases the photostability of P(V)Pcs. Moreover, it has been shown in the example of β-BuO-substituted P(V) that the photostability depends on the nature of axial ligands and increases in the next row: OPh < OMe < OH. The presence of oxy/hydroxy axial ligands on the P(V) atom makes it possible to switch the photochemical and photophysical properties of P(V)Pcs by changing the acidity of the media.

Hydrogen Bond-Mediated Conjugates Involving Lanthanide Diphthalocyanines and Trifluoroacetic Acid (Lnpc2@TFA): Structure, Photoactivity, and Stability

The interaction between lanthanide diphthalocyanine complexes, LnPc₂ (Ln = Nd, Sm, Eu, Gd, Yb, Lu; Pc = C₃₂H₁₆N₈, phthalocyanine ligand) and trifluoroacetic acid (TFA) was investigated in benzene, and the stability of the resulting molecular system was assessed based on spectral (UV-Vis) and kinetic measurements. Structural Density Functional Theory (DFT) calculations provided interesting data regarding the nature of the bonding and allowed estimating the interaction energy between the LnPc₂ and TFA species. Conjugates are created between the LnPc₂ and TFA molecules via hydrogen bonds of moderate strength (>N∙∙H··) at the meso- -bridges of the Pc moieties, which renders the sandwich system to flatten. Attachment of TFA is followed by rearrangement of electronic density within the chromophore system of the macrocycles manifested in considerable changes in their UV-Vis spectra and consequently the color of the studied solutions (from green to orange). The LnPc₂@TFA conjugates including Nd, Sm, Eu, and Gd appeared evidently less photostable when exposed to UV radiation than the related mother compounds, whereas in the case of Yb and Lu derivatives some TFA-prompted stabilizing effect was noticed. The conjugates displayed the capacity for singlet oxygen generation in contrast to the LnPc₂s itself. Photon upconversion through sensitized triplet-triplet annihilation was demonstrated by the TFA conjugates of Nd, Sm, Eu, and Gd.

Solvent effects on molecular aggregation of highly water-soluble phthalocyanines

Molecular aggregation phenomena of a highly water-soluble, metal-free phthalocyanine, H[Formula: see text]Pc, and its copper complex, Cu(Pc); where Pc denotes tetrakis{(2[Formula: see text],6[Formula: see text]-dimethyl-4[Formula: see text]-sulfonic acid)phenoxy}phthalocyaninate) in water, ethanol, and their mixed solvent systems have been investigated by spectroscopic approach In both aqueous and ethanolic solutions, H[Formula: see text]Pc molecules aggregate in a slipped-cofacial manner, although very weakly in ethanol. On the other hand, Cu(Pc) molecules aggregate in a cofacial manner in water while aligning in a slipped-cofacial manner in ethanol. Magnetic circular dichroism spectroscopy was undertaken to investigate aggregation behaviors of Cu(Pc) in water and ethanol. Presence of 4-phenylpyridine in ethanol effectively inhibited aggregation of Cu(Pc) molecules, although little affected the spectra of the monomers. In a mixed solvent system, where water/ethanol [Formula: see text] 10/90 (v/v), Cu(Pc) is free from aggregation up to almost 10[Formula: see text] M. Driving forces of this molecular aggregation are discussed on the basis of [Formula: see text]–[Formula: see text] interaction and coordination chemistry involving copper ions.

Amphoteric phosphorous(V)-phthalocyanines as proton-driven switchable fluorescers toward deep-tissue bio-imaging

Spectral (optical absorption and emission) properties of three amphoteric phosphorous(V)-phthalocyanine derivatives, [P(Pc)(O)OH], where Pc=tetra(tert-butyl)phthalocyaninate (tbpc), tetrakis(2',6'-dimethylphenoxy)phthalocyaninate (tppc), and octakis(4'-tert-butylphenoxy)phthalocyaninate (obppc), have been investigated in ethanolic solutions. Spectral changes upon protonation/deprotonation (the reaction sites have been determined to be their axial ligands by magnetic circular dichroism study) are drastic and rapid. All the initial ([P(Pc)(O)OH]), protonated ([P(Pc)(OH)₂]⁺), and deprotonated ([P(Pc)(O)₂]^-) species are possessed with sufficient brightness (defined as the product of their molar extinction coefficient, ε (inM^-1cm^-1), and fluorescence quantum yield, Φ_F) in bio-imaging window (650-900nm). For example, spectral characteristics of the tbpc derivatives have been determined as follows: ε=1.65×10⁵ (absorption maximum 676nm) and Φ_F=0.80 (emission maximum 686nm) for [P(tbpc)(O)(OH)] while ε=1.45×10⁵ (697nm) and Φ_F=0.27 (714nm) for [P(tbpc)(OH)₂]⁺, and ε=2.25×10⁵ (662nm) and Φ_F=0.90 (667nm) for [P(tbpc)(O)₂]^-. Emission of tppc and obppc derivatives behave in essentially the same manner irrespective of nature of the peripheral substituents and hence Φ_F values are greater with increasing emission peak wavenumbers in line with the "energy gap law". These characteristics make these compounds promising candidates as chemical probes for deep-tissue bio-imaging.

Azaporphyrin phosphorus(v) complexes: synthesis, structure, and modification of optical properties

Azaporphyrinoids, such as phthalocyanines (Pcs), tetraazaporphyrins (TAPs), and tetrabenzotriazacorroles (TBCs), are some of the most well-known and successful artificial dyes and pigments in modern material chemistry.