Yoshinobu Nishimura

Violet emission observed from phthalocyanines

Spectral features of violet emission observed from phthalocyanines in addition to the well-known strong red emission are presented. The origin of the violet emission from the present and reported phthalocyanines is argued based upon the observed and estimated features.

UV light and red light chemistry of metallophthalocyanine : wavelength-dependent photochemical reduction of tetrasodium salts of Zn(II) and Cu(II) tetrasulphonatophthalocyanines with amines

Abstract Irradiation of tetrasodium salts of zinc(II) (Na + 4 ZnPcS 4− ) and copper(II) (Na + 4 CuPcS 4− ) tetrasulphonatophthalocyanine in the presence of triethanolamine, triethylamine or ethylenediaminetetraacetic acid in degassed aqueous acetonitrile (1:1 by volume) with red light at 656 nm exciting their Q band did not induce any reaction but that with UV light at 365 nm exciting their Soret band led to their reduction. The reciprocal quantum yields for photoreduction of ZnPcS 4− and CuPcS 4− on 365 nm excitation increased with increasing concentration of the amines. The mechanism of the reaction was discussed and participation of a higher excited state of the phthalocyanines was suggested.

Photosensitized protein damage by dimethoxyphosphorus(V) tetraphenylporphyrin

For the purpose of the basic study of photodynamic therapy, the activity of the water-soluble P(V)porphyrin, dimethoxyP(V)tetraphenylporphyrin chloride (DMP(V)TPP), on photosensitized protein damage was examined. The quantum yield of singlet oxygen generation by DMP(V)TPP (0.64) was comparable with that of typical porphyrin photosensitizers. Absorption spectrum measurement demonstrated the binding interaction between DMP(V)TPP and human serum albumin, a water-soluble protein. Photo-irradiated DMP(V)TPP damaged the amino acid residue of human serum albumin, resulting in the decrease of the fluorescence intensity from the tryptophan residue of human serum albumin. A singlet oxygen quencher, sodium azide, could not completely inhibit the damage of human serum albumin, suggesting that the electron transfer mechanism contributes to protein damage as does singlet oxygen generation. The decrease of the fluorescence lifetime of DMP(V)TPP by human serum albumin supported the electron transfer mechanism. The estimated contribution of the electron transfer mechanism is 0.64. These results suggest that the activity of DMP(V)TPP can be preserved under lower oxygen concentration condition such as tumor.

Synthesis and photophysical properties of water-soluble dendrimers bearing a phthalocyanine core

Aggregation behaviors of phthalocyanine derivatives which have a dendritic structure were examined in an aqueous solution. We prepared the first- and second-generation dendrimers (WG1-PC and WG2-PC), having water-soluble substituents as a peripheral group, to be resolved in water. From spectroscopic measurement, WG2-PC acted in a monomeric manner, even in an aqueous solution, in contrast to WG1-PC, which exhibited spectra attributed to aggregation. This implies that a higher generation of water-soluble dendrimers can prevent a phthalocyanine core from forming an aggregation. The introduction of the second-generation dendrons to an aggregatable core may be effective to avoid self-aggregation and an undesirable deactivation process.

Control of Singlet Oxygen Generation Photosensitized by meso‐Anthrylporphyrin through Interaction with DNA

To control the activity of photosensitized singlet oxygen (1O2) generation, the electron donor‐connecting porphyrin, 5‐(9′‐anthryl)‐10,15,20‐tris(p‐pyridyl)porphyrin (AnTPyP), was designed and synthesized. AnTPyP became water‐soluble by the protonation of the pyridyl moieties in the presence of 5u2003mm trifluoroacetic acid (pH 2.3). The photoexcited state of the porphyrin ring in an AnTPyP molecule was effectively deactivated by intramolecular electron transfer from the anthracene moiety within 0.04u2003ns in an aqueous solution. The deactivation was suppressed by the interaction with a DNA strand, resulting in the elongation of the lifetime of the porphyrin excited state and the enhancement of the fluorescence intensity. Furthermore, it was confirmed that the interaction enabled the photoexcited AnTPyP to generate 1O2. Selective 1O2 generation by forming a complex with DNA should be the initial step to realize the target selective photodynamic therapy.

Fluorescence Sensor with A New ON1–OFF–ON2 Switching Mechanism Using the Excited State Intermolecular Proton Transfer Reaction of An Anthracene-diurea Compound

A new photoreaction mechanism of “Three‐state molecular switch” fluorescence sensor based on ON1‐OFF‐ON2 sequence was achieved by anthracene‐diurea compound, which was designed using two phenylurea groups and one anthracene, 9,10BtDSPUA. Photochemical properties of 9,10BtDSPUA and interaction between 9,10BtDSPUA and anion were investigated in detail by absorption, 1H NMR, fluorescence, and fluorescence decay measurements. While the fluorescence of 9,10BtDSPUA in DMSO (ON1) was quenched in the presence of low concentration of acetate anion (OFF), fluorescence enhancement occurred by the addition of high concentration of acetate anion (ON2). This compound forms complex with acetate anion through hydrogen bonding interaction in the ground state resulted in tautomer formation by excited state intermolecular proton transfer (ESIPT) on irradiation. Whereas single coordination of acetate anion to anthracene‐diurea compound may cause fluorescence quenching, full coordination may cause fluorescence enhancement due to suppressing ESIPT. This suppressing ESIPT was occurred by electron‐donating resonance effect between two urea moieties. This study is the first example of ON1‐OFF‐ON2 fluorescence sensor for concentration detection of acetate anion.

Time-resolved fluorescence of α,ω-di(1-naphthyl)oligosilanes and 1-naphthyloligosilanes: intramolecular excimer formation and charge-transfer interactions

The intramolecular photochemical processes excimer formation and charge-transfer (CT) complex formation were investigated by comparing the behavior of α,ω-di(1-naphthyl)permethyloligosilanes ((1-naphthyl)-(SiMe2)n-(1-naphthyl); NSnN, nxa0=xa01, 3, and 6) and 1-(1-naphthyl)permethyloligosilanes ((1-naphthyl)-(SiMe2)n-Me; NSn, nxa0=xa01, 3, and 6) by use of stationary and time-resolved fluorescence (TR-FL) measurements. Formation of excimer and CT complexes is highly dependent on the silicon chain length and polarity of the medium.Graphical AbstractIntramolecular excimer formation between the two naphthyl groups and charge transfer interactions between the naphthyl and silane moieties were investigated by use of a time-correlated single-photon counting method.