摘要:

A colorless toluene solution of benzo[1,2,3-kl:4,5,6-k′l′]dixanthene endoperoxide (BDXepo)1slowly changes to red BDX2, by refluxing at 110°C in toluene. However, in the presence of HCl,2was formed more rapidly from1even at room temperature. A novel dosimetry system was proposed using1and acid generating materials such as chlorinated alkanes. A chloroform solution of1([1] = 1.0 × 10−3M) gave red color of2after irradiation with γ ray at 73 Gy.

ISSN:1058-725X    

DOI:10.1080/10587250008023916

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We have measured the transient absorption of a negative photochromic spiropyran derivative, 3′,3′-dimethyl-6,8-dinitro-1′-octadecylspiro[(2H)- 1-benzopyran-2′,2 -indoline] by a nanosecond laser photolysis, in order to elucidate the dynamical behavior of the negative photochromic reactions. On visible light photolysis, the intensity of the absorption bands of the merocyanine (MC) form decreases and that of the spiropyran (SP) form increases. The transient absorption of the MC form consists of three bleaching components with the time constants of ≤25 ns, 240 ns and 3.4 μs. On the other hand, the transient absorption of the SP form has two rising components with the time constants of 620 ns and 4.0 μs. Based on the analogy to the photochromic reaction of the positive photochromic spiropyrans, the reaction pathway from the MC to SP form of the negative photochromic spiropyrans is discussed.

ISSN:1058-725X    

DOI:10.1080/10587250008023917

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Transient absorption of 2-(2,4-dinitrobenzyl)pyridine (α-DNBP) has been measured by a nanosecond laser photolysis to elucidate the dynamical behavior of a photoinduced intramolecular proton transfer (PIPT). On UV light photolysis, α-DNBP changes from a colorless to a dark blue form. The dark blue form consists of the OH, OH−and NH forms whose absorption bands are located at ∼400, ∼490 and ∼570 nm, respectively. We found an additional absorption band located at 660 nm. From the observed transient behavior of the band, we assign this band to be the lowest absorption band of the OH form. The PIPT reaction pathways and their time constants of α-DNBP also have been determined.

ISSN:1058-725X    

DOI:10.1080/10587250008023918

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Picosecond time-resolved resonance Raman (TR3) spectroscopy was used to study the dynamics and structure of transient species involved in the photochromic process in solution of 1,3,3-trimethylspiro[indoline-naphthoxazine]. TR3spectra recorded in n-hexane, at 10 ps and 50 ps time-delays were compared with those obtained on the ns-ms timescale and to the resonance Raman spectrum of a permanent opened form. These data and the results of a detailedab initiovibrational analysis, have allowed us to determine the structure of the tran-soid isomer already present at 10 ps and to precise the photochromic mechanism.

ISSN:1058-725X    

DOI:10.1080/10587250008023919

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Ultrafast dynamics of photoinduced electron transfer reaction and dimer radical cation formation of ion pair charge transfer complexes between dicyanovinylstyrylpyridinium cation and tetraphenylborate anion were studied at room temperature in less polar solvents by femtosecond laser flash photolysis. Transient absorptions were observed both in the visible and near-infrared regions. They showed very rapid rise in less than one picosecond, which was limited by the time resolution of our flash photolysis system.

ISSN:1058-725X    

DOI:10.1080/10587250008023920

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Transient absorption spectroscopy with femtosecond time resolution was used to probe the photochemical ring opening process of 3,3-diphenylnaphtho[2,1-b] pyran in solution. Analysis of the temporal evolution of the spectra from 0.4 ps to 100 ps has allowed us to detect and identify some of the intermediates involved in the photochemical formation of colored photomerocyanine isomers. From these data and those of recentab initioand semi-empirical calculations on related photochromic systems, a simple mechanistic model was proposed for the ring opening/closing reaction in room temperature solution.

ISSN:1058-725X    

DOI:10.1080/10587250008023921

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

3-Phenyl- and 3-(2-naphthyl)isochromene show light-intensity-dependent photochromic behavior; the excitations with low- and high-intensity laser pulses produce isomeric open forms by way of one-photon and two-photon processes, respectively, their lifetimes being in the hundred-nanosecond and hundred-microsecond orders, respectively.

ISSN:1058-725X    

DOI:10.1080/10587250008023922

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A novel water-soluble polyazobenzene dendrimer modified with L-lysines at the periphery was synthesized. The results from light scattering and gel filtration chromatography showed that the particle size is controllable upon UV or visible light irradiation. Furthermore, a gel shift assay with plasmid DNA and an electrophoretic light scattering analysis demonstrated that the affinity of this cationic dendrimer toward DNA is photo-controllable on the basis of zeta potential alteration on dendrimer's surface.

ISSN:1058-725X    

DOI:10.1080/10587250008023923

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Products μβ of the first order hyperpolarisabilities β of both isomers of dithienyl ethene derivatives by their ground state dipole moments μ have been determined experimentally by the EFISHG technique, then calculated by a semi-empirical method. Both calculations and measurements put into evidence a large increase in μβ in going from the open isomer (OF) to the largely π conjugated closed isomer (CF). This photoinduced change in second order NLO coefficient is used to modulate the Second Harmonic Generation (SHG) signal generated by a PMMA film doped with one diarylethene under alternate irradiation with UV (325 nm) and visible (514 nm) light.

ISSN:1058-725X    

DOI:10.1080/10587250008023924

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

As a system, which put the optical neuro-computing into practice, a novel architecture based on organic photochromism was described. The performance of the system was examined concretely by means of computer simulation. Based on the result, a prototype system was constructed using a bulk amorphous thin film of diarylethene to prove the feasibility of the architecture. Using the prototype, preliminary experiment was carried out to confirm the function of optical data inscription and parallel analog operation. New concept of data processing device was also suggested from the discussion over the characteristics of the system.

ISSN:1058-725X    

DOI:10.1080/10587250008023925

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor