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1.
《Chemical physics letters》2001,331(3-4):198-205
The spectroscopic and photophysical properties for a series of bis-adduct derivatives of C60 have been studied using a combination of time-resolved and steady state techniques, including picosecond single photon counting and laser flash photolysis. The electronic absorption and fluorescence spectra are red shifted with respect to those of C60. As with the parent fullerene, the main deactivation channel of the excited singlet state is intersystem crossing with the yields of singlet oxygen ranging from 0.63 to 0.97. Our results demonstrate that the photophysical properties depend on the addition pattern of the addends. 相似文献
2.
Photophysical Properties of the Cationic Form of Neutral Red 总被引:1,自引:0,他引:1
M. K. Singh H. Pal A. C. Bhasikuttan A. V. Sapre 《Photochemistry and photobiology》1999,69(5):529-535
Abstract— Photophysical properties of the cationic form of neutral red (NRH+ ), a phenazine-based dye of biological importance, have been investigated in several protic and aprotic solvents using optical absorption, steady-state and time-resolved fluorescence and picosecond laser flash photolysis techniques. Absorption and fluorescence characteristics of the dye in protic solvents indicate the existence of intermolecular hydrogen bonding between the NRH+ and solvent molecules in the ground state as well as in the excited state. Measurements of the fluorescence lifetime in normal and heavy water also support the formation of intermolecular hydrogen bonding. Time-resolved transient absorption spectra obtained in the picosecond laser flash photolysis experiments show only the absorption band due to the Sn ← S1 absorption. The picosecond transient absorption results do not indicate any spectral shifts attributable to the hydrogen bond formation dynamics between the excited NRH+ and the protic solvent molecules. It is inferred that the hydrogen bonding dynamics are much faster than the time resolution of our picosecond setup (∼35 ps). 相似文献
3.
We have developed a picosecond flash photolysis method together with transient spectral measurements over the entire visible, and some parts of the near UV and near IR regions. Sn ← S1 absorption spectra of anthracene were obtained as microdensitometer tracings of photographs throughout the region 390–920 nm. Some other results of picosecond studies on the primary processes in exciplexes are also reported briefly. 相似文献
4.
5.
F. Wilkinson 《Journal of Chemical Sciences》1991,103(3):305-311
Recent progress which allows laser flash photolysis investigation of opaque materials by using diffuse reflectance from analysing
sources for the detection of laser induced transient species is described. Experimental details of nanosecond and picosecond
diffuse reflectance laser photolysis systems are presented and methods of analysis of data are discussed. The potential of
the technique for studying elementary reactions at interfaces is demonstrated with particular reference to bimolecular reactions
of (a) the triplet state of acridine adsorbed on various porous silica surfaces and (b) ion-electron recombination following
multi-photon ionisation of diphenyl polyenes adsorbed on γ-alumina. The mechanisms of formation and decay of these transient
adsorbed species are discussed. 相似文献
6.
Ya. N. Malkin N. A. Lysak S. A. Tikhomirov G. B. Tolstorozhev V. A. Lokshin V. A. Kuz'min 《Russian Chemical Bulletin》1987,36(9):1979-1982
Conclusions Photoexcitation of a solution of 6-nitrospiro(2H-l-benzopyran)-2,2-isobenzofuran under picosecond laser photolysis conditions leads to cleavage of a C-O bond in a Franck-Condon state and formation of a shortlived cis-cisoid isomer of the merocyanine form of the spiropyran.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2129–2132, September, 1987. 相似文献
7.
Transient absorptions in HITC are investigated in the range 650-950 nm by a conventional flash photolysis technique and “picosecond” spectroscopy with a train of 6 to 7 pulses. This study gives evidence for S1-Sn absorption, photoisomer and triplet generation. The comparison between experimental data and computer solutions allows the determination of the rate constants of these processes and molar extinction coefficients of the absorption spectra. Taking into account these results, we discuss the limitations of the performances of the flashlamp excited HITC dye laser. 相似文献
8.
The fluorescence quenching reaction of 2-naphthylamine and 1-pyrenol due to hydrogen bonding interaction with pyndine has been investigated Absorption spectra due to the state formed by charge transfer from excited naphthylamine to hydrogen bonded pyridine have been observed by means of picosecond laser photolysis. 相似文献
9.
Sakamoto M Cai X Kim SS Fujitsuka M Majima T 《The journal of physical chemistry. A》2007,111(2):223-229
The electron transfer from the benzophenone ketyl radical in the excited state (BPH(.-)(D(1))) to several quenchers (Qs) was investigated using nanosecond/picosecond two-color two-laser flash photolysis and nanosecond/nanosecond two-color two-laser flash photolysis. The electron transfer from BPH(.-)(D(1)) to Qs was confirmed by the transient absorption and fluorescence quenching measurements. The intermolecular electron-transfer rate constants were determined using the Stern-Volmer analysis. The driving force dependence of the electron-transfer rate was revealed. 相似文献
10.
Murakami M Miyasaka H Okada T Kobatake S Irie M 《Journal of the American Chemical Society》2004,126(45):14764-14772
The cycloreversion (ring-opening) process of one of the photochromic diarylethene derivatives, bis(2-methyl-5-phenylthiophen-3-yl)perfluorocyclopentene, was investigated by means of picosecond and femtosecond laser photolysis methods. The drastic enhancement of the reaction yield was observed only by the picosecond laser exposure. The excitation intensity effect of the reaction profiles revealed that the successive multiphoton absorption process leading to higher excited states opened the efficient cycloreversion process with a reaction yield of (50 +/- 10)%, while the one-photon absorption directly pumped to a higher excited state did not lead to the efficient cycloreversion reaction. These results indicate that not the energy of the excitation but the character of the electronic state takes an important role in the enhancement of the cycloreversion reaction. 相似文献
11.
Chung-Lu Hsieh M. A. El-Sayed Malcolm Nicol Mark Nagumo † Jai-Hyung Lee † 《Photochemistry and photobiology》1983,38(1):83-94
Abstract— Resonance Raman spectra of the picosecond bacteriorhodopsin intermediate(s) have been obtained by microbeam, flow and subtraction techniques using a synchronously pumped, cavity-dumped dye laser. Nanosecond spectra also were measured with this laser by cavity dumping without mode-locking. The picosecond spectra in the fingerprint region, which is sensitive to the configuration of the retinal chromophore, differ from spectra of the parent bR570 but could be correlated to the spectrum of bRDA550 , a “13-cis” species which has been determined from spectra of bR570 and bRDA560. The picosecond transient and bRDA550 also are similar in the 950–1050 cm-1“deuteration fingerprint” region when the medium is changed from H2O to D2O. These results suggest that trans—cis isomerization occurs during the 40-ps pulse duration. The shift relative to the parent bR570 in the ethylenic stretch region suggests that the picosecond and nanosecond transients absorb at wavelengths longer than 570 nm. The C band at 1646 cm-1 is found to shift or to broaden upon photolysis in the picosecond time scale. This might suggest a change in the electronic structure of the group and its environment on the picosecond time domain. The nanosecond spectra obtained in this work (with 15-ns pulses) are similar to the spectra previously observed on the 100-ns time scale but are slightly different from the picosecond spectrum. These data suggest that more than one transient species appears on the picosecond-to-nanosecond time scale. The temporal evolution of Raman bands in the fingerprint as well as the low energy (950–1050 cm-1) region and its implications are discussed. 相似文献
12.
Kumao Hamanoue Hiroshi Teranishi Masami Okamoto Yoh Furukawa Seiichi Tagawa Yoneho Tabata 《Journal of polymer science. Part A, Polymer chemistry》1980,18(1):91-100
Photochemical reactions of N-vinylcarbazole (VCZ) in the binary solvent of benzonitrile (?CN) and nitrobenzene (?NO2) were investigated. Both solvent and oxygen effects on the final products were examined. Benzonitrile and nitrobenzene behaved differently in the photochemical reaction of VCZ. At higher concentrations of benzonitrile in the aerated system, cyclodimerization was favored and it was inhibited by a cation scavenger and retarded by a radical scavenger. Polymerization occurred in the deaerated system and was inhibited by a radical scavenger and not by a cation scavenger. Using picosecond laser photolysis it was concluded that cyclodimerization occurs through the diffusion-controlled encounter collision of the excited singlet state of VCZ with an oxygen molecule, producing the VCZ cation radical and oxygen anion radical, and that this oxygen anion radical plays a very important role in the cyclodimerization of VCZ. It was also suggested that radical polymerization in the deaerated system is initiated by the excited triplet state of VCZ. On the other hand, at higher concentrations of nitrobenzene, only cationic polymerization took place irrespective of the presence of oxygen, and it was suggested that a contact charge-transfer complex is produced by the mixing of VCZ with ?NO2 producing VCZ cation radical and NO2 anion radical by an excited-state electron transfer. 相似文献
13.
E. M. Glebov I. P. Pozdnyakov V. P. Chernetsov V. P. Grivin A. B. Venediktov A. A. Melnikov S. V. Chekalin V. F. Plyusnin 《Russian Chemical Bulletin》2017,66(3):418-425
Photosolvation of a PtIV hexathiocyanate complex Pt(SCN)6 2– in water and ethanol was studied by steady-state photolysis, nanosecond laser flash photolysis, and ultrafast kinetic spectroscopy. Complexes Pt(SCN)5(H2O)– and Pt(SCN)5(C2H5OH)– were found to be the only reaction products. The quantum yields of photosolvation are independent of the excitation wavelength, being equal to 0.25 and 0.5 for the solutions of the complex in water and ethanol, respectively. Photosolvation proceeds by the mechanism of heterolytic metal—ligand bond dissociation without involvement of redox processes. The characteristic time of formation of the end products for both solvents is about 10 ps. Three successive intermediates detected on the picosecond time scale were interpreted as PtIV complexes. The nature of the intermediates and possible mechanisms of photosolvation are discussed. 相似文献
14.
V. A. Nadtochenko P. P. Levin N. L. Zaichenko F. E. Gostev I. V. Shelaev A. I. Shienok L. S. Kol’tsova O. M. Sarkisov A. A. Berlin 《High Energy Chemistry》2013,47(3):120-126
Intramolecular processes occurring in a photobifunctional compound (PBC) comprising the spironaphthopyran and hydroxyazomethine moieties have been studied in methanol solutions by femtosecond laser photolysis using light with wavelengths of 340 and 490 nm. At the excitation wavelength of 490 nm, the cis-trans photoisomerization in the azomethine moiety occurs in the S1 state. In the case of PBC photolysis with 340-nm light, the opening of the spiro bond of the spiropyran moiety (formation of the X form) also takes place during relaxation of the Sn state to the S1 state followed by isomerization to the merocyanine form. The spectral and kinetic characteristics of different electronically excited have been were determined. The data have been compared with those of nanosecond laser photolysis. 相似文献
15.
Douglas Magde Maurice W. Windsor Dewey Holten Martin Gouterman 《Chemical physics letters》1974,29(2):183-188
From picosecond flash photolysis and spectroscopy, the absorption spectra of the first excited singlet S1 and of the first excited triplet T1 of (OEP)SnCl2 are determined; we also determine triplet quantum yield, φt ≈ 0.80. Similar S1 and T1 phototransient absorption spectra occur in (OEP)Pd. However, two Cu porphyrins show only one phototransient absorption spectrum. Our T1 absorption results are generally consistent with the available earlier spectroscopic studies made with other techniques. Our value for φt lies intermediate between values given by two earlier studies, which were based on two different methods. 相似文献
16.
Photochemical and photophysical processes of organosilicon compounds have been studied. Dual (local and CT) emission has been found in aromatic disilanes. The intramolecular CT fluorescence has a broad and structureless band with a large Stokes shift. The CT process in the excited state occurs very rapidly with a time constant less than 10 ps even in rigid glass at 77 K This finding shows that the CT mechanism is quite different from TICT (or OICT) which needs twisting or internal rotation during the lifetime in the excited state. The CT emission originates from the 1(2pσ,3dσ) state having an in-plane long-axis polarization, which is produced by the 2pσ* (aromatic ring) vacant 3dσ (Si-Si bond) intramolecular charge transfer. The CT state plays an important role in the photochemical and photophysical properties of phenyldisilanes. At room temperature a long-lived 425 nm transient (silene) is produced with a time constant of 30 ps from the CT state. The photolysis of cyclotetrasilanes is remarkably dependent on their molecular structures: two molecules of the corresponding disilene are produced from the S1 state of planar cyclotetrasilanes, while silylene is generated by ring contraction in the S1 state of bent cyclotetrasilanes. Remarkably large Stokes shifts are observed in these cyclotetrasilanes. Dimethylsilylene with a transient peak at 470 nm is observed by laser photolysis of cyclohexasilanes. The dynamic behaviours of the intermediates have been studied by nanosecond laser photolysis. The phenylsilyl radical is generated by photolysis of phenylsilanes in rigid glass at 77 K, which gives a structured emission similar to that of benzyl radical. 相似文献
17.
I. P. Pozdnyakov E. M. Glebov S. G. Matveeva V. F. Plyusnin A. A. Mel´nikov S. V. Chekalin 《Russian Chemical Bulletin》2015,64(8):1784-1795
Primary photophysical and photochemical processes were studied for PtIVBr6 2– and PtIVCl6 2– complexes in water and methanol by ultrafast kinetic spectroscopy upon excitation in the band region of charge transfer from the ligand-centered group π-orbitals to the eg*-orbital of PtIV complex anion (LMCT bands). The data obtained earlier upon excitation in the region of d—d bands were compared. Irrespective of the excitation wavelength, the photochemical properties of complexes are caused by the reactions of intermediates proceeding in the picosecond time range. These intermediates were identified as PtIVBr5 – upon photolysis of PtIVBr6 2– and, presumably, the Adamson radical pair [PtIIICl5 2–(C 4v )...Cl?] upon photolysis of PtIVCl6 2–. The difference in the exciting light wavelengths has an impact only on the first step of these processes, i.e., transition from the Franck—Condon excited state to intermediates. 相似文献
18.
We show that the open period of a CS2 light gate, triggered by a picosecond optical pulse, depends on the optical pathlength through the CS2. An alternative to the light gate is suggested for time resolved spectroscopy. The working principle is based on scattering induced in CS2. We have found that the broadband emission from H2O or D2O excited by a 5300 Å picosecond pulse is also of picosecond duration, but the blue part is delayed with respect to the red. From this delay time the lifetime of the ground state vibrational levels may be measured directly. 相似文献
19.
State Selectivity and Dynamics in Dissociative Electron Attachment to CF3I Revealed through Velocity Slice Imaging
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Dr. Frímann H. Ómarsson Prof. Dr. Nigel J. Mason Prof. Dr. E. Krishnakumar Prof. Dr. Oddur Ingólfsson 《Angewandte Chemie (International ed. in English)》2014,53(45):12051-12054
In light of its substantially more environmentally friendly nature, CF3I is currently being considered as a replacement for the highly potent global‐warming gas CF4, which is used extensively in plasma processing. In this context, we have studied the electron‐driven dissociation of CF3I to form CF3? and I, and we compare this process to the corresponding photolysis channel. By using the velocity slice imaging (VSI) technique we can visualize the complete dynamics of this process and show that electron‐driven dissociation proceeds from the same initial parent state as the corresponding photolysis process. However, in contrast to photolysis, which leads nearly exclusively to the 2P1/2 excited state of iodine, electron‐induced dissociation leads predominantly to the 2P3/2 ground state. We believe that the changed spin state of the negative ion allows an adiabatic dissociation through a conical intersection, whereas this path is efficiently repressed by a required spin flip in the photolysis process. 相似文献
20.
Solid state photolysis of strontium and barium tris(oxalato) ferrate(III) was done under a medium pressure lamp and investigated with Mössbauer spectroscopy. The product [FeII(C2O4) (H2O)2]2? formed during photolysis is found to be quite stable and does not convert to ferric state on long standing in air. 相似文献