Tsuguo Yamaoka

Photosensitizer efficacy of non-peripheral substituted alkylbenzopyridoporphyrazines for photodynamic therapy of cancer

The triplet state of zinc non-peripheral substituted alkylbenzopyridoporphyrazines and position isomers were measured, using laser-flash photolysis in poly(methyl methacrylate) film. The triplet lifetime increased with an increasing pyridine number in the molecule. The lowest symmetric isomer having two pyridine rings in the molecule showed the longest triplet state lifetime. The compound was suitable for the use the photosensitizer as a photodynamic therapy of cancer.

Photochemistry of Naphthalimide Photoacid Generators

The photophysical properties of a series of 1,8-naphthalimide photoacid generators were studied by steady state fluorescence and phosphorescence spectroscopy. Emission and excitation anisotropies, triplet quantum yields in polar and nonpolar solvent and photoacid generation were evaluated. The singlet excited state exhibits a low polarity and is strongly deactivated by an efficient intersystem crossing process. In protic solvent, a homolytic singlet cleavage of the N-O bond occurs and leads to the acid production. The existence of a triplet state close to the singlet state was clearly evidenced. The presence of close singlet excited states is supported by fluorescence anisotropy and picosecond laser spectroscopy experiments. Results of DFT calculations well confirm the experimental contentions and yield important information about the cleavage process involved in such compounds.

Light-intensity dependence in the photochromism of dibenzo[2.2](4,4′)-azobenzenophane

Reduction of 4′,4″-dinitro-o-terphenyl under conditions of high dilution, produces a mixture of macrocyclic poly(azobenzene) compounds. From the mixture, three kinds of macrocycle, namely, dimer 2{dibenzo[2.2](4,4′)azobenzenophane}, trimer 3 and tetramer 4 have been isolated pure. In toluene, absorption peaks due to the π→π* transition for the macrocycles undergo dramatic hypsochromic shifts as the ring size of the macrocycles decreases from the trimer 3 to the dimer 2; this is an indication that benzene rings at both ends of the dimer 2 are fixed perpendicularly to two azobenzene planes in the macrocycle. The photostationary state of the dimer 2 in toluene at λ= 366 nm contained the EZ isomer which undergoes thermal isomerization to the more stable EE isomer at the first-order rate of 0.768 s–1. The reaction of 2 is much faster than that of the dimer 5, which was described in our last paper. Due to the fast thermal EZ to EE isomerization, the efficiency of the photoisomerization from the EE isomer to the ZZ isomer is light-intensity dependent. This dependence is observed at higher light intensities for the dimer 2 than for the dimer 5.

Photoreversible optical nonlinearities of polymeric films containing spiropyran with long alkyl chains

It was demonstrated that the third‐order optical nonlinearity of polymer films could be reversibly controlled by the photochromic conversion and following J‐aggregate formation of spiropyran embedded in an inert polymer matrix. Patterns consisting of areas with high and low third‐order nonlinear optical activities were prepared by imagewise exposure of the photochromic films followed by thermal treatment to form thermally stable J aggregates of photoinduced merocyanine in the exposed area. This system could be useful in developing new unconventional optical devices based on optical nonlinearities, including new types of spatial light modulators.

A photochromic memory with a non-destructive read-out property

Abstract Isomerizations of [2.2](4,4′)-azobenzenophane (1) in polycarbonate films were investigated spectrophotometrically, and the light-intensity dependent efficiency of the photoisomerization of macrocyclic azobenzene dimers, including 1, was analyzed theoretically. It is demonstrated that the efficiency of photoisomerization of 1 is dependent on the light intensity, even in a polymer film. A correlation between the lifetimes of the trans-cis isomers of macrocyclic azobenzene dimers and light intensities, where the efficiency of photoisomerization becomes dependent on light intensity, is also described. A photochromic memory composed of 1 and polycarbonate shows a non-destructive read-out property.

Sensitization mechanisms from excited-singlet state of pyrromethene dye to a radical-generating reagent in a poly(methylmethacrylate) film

The sensitization mechanisms of a pyrromethene dye with a radical-generating reagent, 3,5,3′,5′-tetramethylpyrromethene-BF2 (BH) with 3,3′,4,4′-tetrakis(t-butyldioxycarbonyl)benzophenone (BP), in a poly- (methylmethacrylate) (PMMA) film were investigated by laser flash phoptolysis using a total reflection cell and single photon counting. From the laser flash photolysis, strong fluorescence was detected though no transient absorption was detected. The fluorescence intensity was significantly decreased with increasing concentration of BP, apparently exhibiting Perrin-type static quenching at a quenching radius, Rf = 26 A. From the examination of decay profile using single photon counting, logarithmic plots of fluorescence decay in a PMMA film afforded a nonlinear, convex reduction, corresponding to a streched exponential decay, while the logarithmic plots in acetonitrile showed a linear relationship. With increasing concentration of BH, the fluorescence maximum was shifted to red, and the intensity of fluorescence was significantly reduced. The red shift of fluorescence, the nonlinear fluorescence logarithmic decay and the large reduction in fluorescence indicate a dispersive photoexcited state and a relaxation of excitation energy hopping across an array of sites with Gaussian energy distribution. Moreover, after incorporating BP, the convex logarithmic plots became more steep, and the fluorescence maximum was also shifted to red, exhibiting a nonstatic quenching process competitive to the excitation energy hopping. Thus the sensitization of photoinitiator system containing BH and BP, whose contents were almost same as that in the commercial products, was due to a static quenching process from dispersive singlet excited BH to BP ground state, and the nonstatic quenching process competitive to the excitation energy hopping was minimal. Copyright

The photo- and thermal cis-trans isomerization of [23](4,4′)azobenzenophane

Four isomers, EEE, EEZ, EZZ and ZZZ, exist for [23](4,4′)azobenzenophane depending on the degree of the isomerization of three azobenzene units. These isomers are stable enough to be separated by reversed-phase liquid chromatography. The compound in methanol exists as the EEE form in the dark. Upon irradiation at 366 nm the EEE form isomerizes via the EEZ form and the EZZ form to the ZZZ form. At the photostationary state at 366 nm, 85% of the compound exists as the ZZZ form. From the photostationary state the compound thermally isomerizes gradually to the EEE form. The thermal reaction from the ZZZ form to the EEE form also proceeds in a stepwise fashion. The relative values of the quantum yields for the photoisomerization and the absolute value of the rate for the thermal isomerization have been determined for each step. Both the photo- and thermal processes in the Z→E direction show the different efficiencies (or rates) depending on the processes. These experimental results can be explained by supposing that the different degree of ring strain works for ground and (or) excited states of each isomer. In this compound, a certain isomer can be enriched by the combination of external stimuli, such as light or heat. This raises the possibility of synthesizing molecules with more than two functional states.

Photoalignment Films of Polyesters with Photoreactive Main Chain

The photoreactive thin films of poly(oxyalkyleneoxy-1,4-phenylenediacryloyl), a PDA-n polyester (n=2–5), were prepared. Their photoreactions and the liquid crystal (LC) photoalignment by irradiation of linearly polarized UV light (LPL) were investigated. The PDA-n polyesters have photoreactive sites in the polymer main chain and not in the side chain which is different from poly(vinyl cinnamate) (PVCi), a well-known photoalignment polymer. These PDA-n thin films show different photoreactivities depending on the number of methylene units, n. Odd-numbered PDA-n polyesters with higher photosensitivity than even-numbered PDA-n polyesters show a dichroism due to irradiation with LPL which results in a homogeneous alignment of the nematic LC.

Mechanistic investigations of the photosensitized reactions of iron arene complexes

Abstract The decomposition of cyclopentadienyliron(II) cumene hexafluorophosphate ([CpFe(Cum)]PF 6 ) was investigated by singlet and triplet sensitization. [CpFe(Cum)]PF 6 quenched the excited state of various sensitizers, and decomposition of [CpFe(Cum)]PF 6 efficiently took place in CH 2 Cl 2 . The quenching rate constants of fluorescence or TT absorption of the sensitizers by [CpFe(Cum)]PF 6 were close to the diffusion rate constants. The rate constants were independent of the exo- or endo-thermicity of the photoinduced electron transfer process assumed to take place. However, they were dependent on the singlet and triplet excitation energies of [CpFe(Cum)]PF 6 and the sensitizers. Thus, the major quenching process would be the singlet and triplet energy transfer. In the case of using 3,3′-carbonyl- bis (7-diethylaminocoumarin) (KC-DA) as a visible-light-sensitizer, the decomposition of [CpFe(Cum)]PF 6 is inefficient, and a photochemically unstable intermediate was generated.

Singlet oxygen generation by tetrabenzoporphyrins as photosensitizer

Abstract The efficiency of the photosensitized generation of singlet oxygen ( 1 O 2 ) with meso -phenyl substituted tetrabenzoporphyrin metallo complexes as sensitizer was determined from the limiting quantum yield of the (+)-limonene photooxygenation and compared with that of hematoporphyrin (HP), which has been known to serve as an effective sensitizer, using a HeNe laser light (633 mm). Among the diamagnetic (Mg, Zn, and Cd) complexes treated here, the Zn complexes were most efficient for the (+)-limonene photooxygenation with the limiting quantum yields of Φ(−A)=0.4. This result was comparable to that of HP. The direct observation of the intensity of 1 O 2 emission by the laser flash photolysis technique supported these results.