Hiroaki Horiuchi

Photophysical Property and Photostability of J-Aggregate Thin Films of Thiacyanine Dyes Prepared by the Spin-Coating Method

By use of electrostatic interactions of dye molecules and poly(diallyldimethylammonium chloride) (PDDA), the spin-coating technique has been successfully applied to the preparation of stable J-aggregate thin films of thiacarbocyanine dyes on a polycarbonate or quartz plate. The J-aggregate thin films were prepared by the spin-coating of PDDA aqueous solution on dye thin films prepared on a substrate by the spin-coating of 2,2,3,3-tetrafluoro-1-propanol solution of dyes. Photophysical properties of the dye thin films and J-aggregate thin films were studied by measuring the fluorescence spectra, quantum yields, and lifetimes. Coherent size of the J-aggregates was estimated to be 3-12 by means of the absorption bandwidth (full width at half maximum) or radiative lifetime. Photostability of the J-aggregate thin films was also studied in terms of photodegradation efficiency under argon and oxygen in comparison with the dye thin films, and J-aggregate thin films were found to be more stable than the corresponding dye thin films.

Silylation Improves the Photodynamic Activity of Tetraphenylporphyrin Derivatives In Vitro and In Vivo

The effects of silyl and hydrophilic groups on the photodynamic properties of tetraphenylporphyrin (TPP) derivatives have been studied in vitro and in vivo. Silylation led to an improvement in the quantum yield of singlet oxygen sensitization for both sulfo and carboxy derivatives, although the silylation did not affect other photophysical properties. Silylation also improved the cellular uptake efficiency for both sulfo and carboxy derivatives, enhancing the in vitro photodynamic activity of the photosensitizer in U251 human glioma cells. The carboxy derivative (SiTPPC4 ) was found to show higher cellular uptake efficiency and in vitro photodynamic activity than the corresponding sulfo derivative (SiTPPS4 ), which indicates that the carboxy group is a more promising hydrophilic group than the sulfo group in the silylated porphyrin. SiTPPC4 was found to show high selective accumulation efficiency in tumors, although almost no tumor selectivity was observed for the nonsilylated porphyrin. The concentration of SiTPPC4 in tumors was 13 times higher than that in muscle 12 h after drug administration. We also studied tumor response after treatment and found that silylation enhanced in vivo photodynamic activity significantly. SiTPPC4 shows higher photodynamic activity than NPe6 with white light irradiation.

Singlet molecular oxygen generation by water-soluble phthalocyanine dendrimers with different aggregation behavior

Phthalocyanines having hydrophilic or lipophilic dendrons were synthesized to investigate the efficiencies of singlet molecular oxygen (1Δg) formation. The introduction of higher generation of dendrons to the central metal (Si) of phthalocyanine in vertical direction to their ring plane has resulted in the successful improvement in avoiding aggregate formation that resulted in efficient generation of 1Δg even in water.

Laser-induced fluorescence of cyclohexadienyl (c-C6H7) radical in the gas phase.

A laser-induced fluorescence spectrum was observed in the 500-560 nm region when a mixture of 1,4-cyclohexadiene and oxalyl chloride was photolyzed at 193 nm. The observed excitation spectrum was assigned to the A (2)A(2)<--X (2)B(1) transition of the cyclohexadienyl radical c-C6H7, produced by abstraction of a hydrogen atom from 1,4-cyclohexadiene by Cl atoms. The origin of the A<--X transition of c-C(6)H(7) was at 18 207 cm(-1). From measurements of the dispersed fluorescence spectra and ab initio calculations, the frequencies of several vibrational modes in both the ground and excited states of c-C(6)H(7) were determined: nu(5)(C-H in-plane bend)=1571, nu(8)(C-H in-plane bend)=1174, nu(10)(C-C-C in-plane bend)=981, nu(12)(C-C-C in-plane bend)=559, nu(16)(C-C-C out-of-plane bend)=375, and nu(33)(C-C-C in-plane bend)=600 cm(-1) for the ground state and nu(8)=1118, nu(10)=967, nu(12)=502, nu(16)=172, and nu(33)=536 cm(-1) for the excited states.

Synthesis, structure, and photochemical reaction of 9,10-dihydro-9-silaanthracene derivatives carrying bulky substituents

Abstract Some of 9-aryl-9,10-dihydro-9-silaanthracenes (1) were prepared and the alkylation of the compounds gave trans-9-aryl-10-alkyl-9,10-dihydro-9-silaanthracenes exclusively. Upon photolysis of a 9-phenyl derivative, 9-phenyl-9-silaanthracene was confirmed by spectroscopic analysis. Also, structural studies of the dihydro compounds were performed by NMR and X-ray.

Photophysical and photochemical processes of 9,10-dihydro-9-silaanthracenes: photochemical generation and electronic structure of 9-phenyl-9-silaanthracene

Abstract Photophysical processes of 9,10-dihydro-9-silaanthracene ( 1 ) and its 9-phenyl derivative ( 2 ) have been studied in 3-methylpentane at 77 K. Photolyses of these compounds have been carried out at 77 K and reaction intermediates have been studied. Carbon-centered radicals and silylenes have been observed for 1 , while for 2 , formation of carbon-centered radicals and 9-phenyl-9-silaanthracene has been confirmed by use of UV–vis absorption spectrum, fluorescence spectrum, fluorescence polarization and results of semi-empirical MO calculations. The electronic structure of 9-silaanthracene has been discussed in comparison with that of anthracene.

pH-Response Optimization of Amino-Substituted Tetraphenylporphyrin Derivatives as pH-Activatable Photosensitizers

Amino-substituted tetraphenylporphyrin derivatives have been designed as pH-activatable photosensitizers for photodynamic cancer therapy. The photophysical processes of the monoamino-substituted derivative N1 and nonsubstituted derivative N0 have been studied. The quantum yields of the fluorescence and photosensitization of singlet oxygen by N1 were very low in the neutral condition (OFF state), but these quantum yields were recovered by adding acid (ON state). These changes were not observed for N0; therefore, N1 is expected to be applicable as a pH-activatable photosensitizer. The ON/OFF switching mechanism of N1 has also been clarified. To optimize the pH response, tri- and tetraamino-substituted derivatives (N3 and N4) have also been explored. The pH response intensified as the number of amino groups increased. Furthermore, the ON/OFF switching ratio of N3 was 100, which is quite high.

Absolute Phosphorescence Quantum Yields of Singlet Molecular Oxygen in Solution Determined Using an Integrating Sphere Instrument

In this paper, we present an integrating sphere instrument for absolute luminescence quantum yield measurements from the visible to near-infrared (NIR) spectral region (λ = 350-1650 nm). The integrating sphere is equipped with a Xe light source and two spectrally corrected multichannel analyzers using a back-thinned charge-coupled device (CCD) and InGaAs detector, one for measurements in the visible to NIR wavelength region (λ = 350-1100 nm) and the other for the NIR wavelength region (λ = 900-1650 nm). The combination of the two optical multichannel analyzers allows measurement of the absolute quantum yield of NIR emissions with good sensitivity. Using this new instrument and platinum(II) meso-tetra(pentafluorophenyl)porphine (PtTFPP) as a sensitizer, we performed the first absolute measurements of quantum yield (Φ(p)(¹Δ)) of the a¹Δ(g) (v′ = 0) → X³Σ(g)⁻ (v″ = 0) emission at 1270 nm from molecular oxygen in different solvents. The quantum yields Φ(p)(¹Δ) in CCl₄ and CS₂ under infinite dilution of sensitizer were determined to be 2.2 × 10⁻² and 6.4 × 10⁻², respectively. Using the Φ(p)(¹Δ) value in CCl₄, the quantum yields in other solvents were determined based on the relative method. From the phosphorescence quantum yields and the lifetimes of O₂(a¹Δ(g)) taken under identical experimental conditions, we evaluated the radiative and nonradiative rate constants of O₂(a¹Δ(g)), which are key parameters to understand the photophysical properties of singlet oxygen in solution. The quantum yields and radiative and nonradiative rate constants obtained in the present study were compared with the literature values determined based on the relative method.

Electronic structure and photochemical reaction intermediates of octakis(1,1,2-trimethylpropyl)octasilacubane

Abstract The electronic spectrum and photochemical reaction intermediates of octakis(1,1,2-trimethylpropyl)octasilacubane have been studied by analyzing the UV-VIS spectrum and transient absorption spectra. The first three absorption bands of the UV-VIS spectrum have been assigned to the transitions from HOMO (t 1u symmetry) to LUMO (a 2u ), from HOMO-1 (t 1g ) to LUMO, and from HOMO to LUMO+1 (t 2g ) by making reference to the results obtained by INDO/S-CI calculations. The photochemical reaction intermediate has been elucidated to be the isomer whose decay rate constant is 57±3 s −1 . The quenching rate constant of the isomer by oxygen is ca. 3×10 5 M −1 s −1 .

Synthesis and Unique Optical Properties of Selenophenyl BODIPYs and Their Linear Oligomers

A series of selenophene-substituted boron-dipyrrin (BODIPY) monomers and selenophene-linked BODIPY oligomers was synthesized. The synthesized BODIPYs show good absorption/emission properties in the red to near-infrared region. Furthermore, some of the selenophenyl BODIPYs are not only useful fluorophores but also good photosensitizers to produce singlet oxygen.