Laser flash photolysis detection of mono- and biradical mesitylene

Time-resolved transient absorption spectra have been obtained first for mesitylene by 355 nm laser flash photolysis at ambient temperature. Mono- and biradicals were observed in the experiment, in which the transient absorption peak at about 370 nm was assigned to the biradical and the peak at about 580 nm to the monoradical; the biradical has a longer lifetime than the monoradical. According to the representative value of the C-H bond dissociation energy for aromatic compounds monoradical formation might be a single-photon process. For comparison with the absorption spectra the time-resolved fluorescence spectra were obtained and also the biradical was assigned to about 393 nm.     

Flash photolysis and pulse radiolysis studies on collagen Type I in acetic acid solution

An investigation of the photochemical properties of collagen Type I in acetic acid solution was carried out using nanosecond laser irradiation. The transient spectra of collagen solution excited at 266 nm show two bands. One of them with maximum at 295 nm and the second one with maximum at 400 nm. The peak at 400 nm is assigned to tyrosyl radicals. The first peak of the transient absorption spectra at 295 nm is probably due to photoionisation producing collagen radical cation. The transient for collagen solution in acetic acid at 640 nm was not observed. It is evidence that there is no hydrated electron in the irradiated collagen solution. The reactions of hydrated electrons and (*)OH radicals with collagen have been studied by pulse radiolysis. In the absorption spectra of products resulting from the reaction of collagen with e(aq)(-) no characteristic maximum absorption in UV and visible light region has been observed. In the absorption spectra of products resulting from the reaction of the hydroxyl radicals with collagen two bands have been observed. The first one at 320 nm and the second one at 405 nm. Reaction of (*)OH radicals with tyrosine residues in collagen chains gives rise to Tyr phenoxyl radicals (absorption at 400 nm).     

Photo-degradation and emission characteristics of benzidine in halomethane solvents

Benzidine is an aromatic base of importance in industry. It represents a serious pollutant in many industrial effluents and its photodegradation is of great interest. The mechanism of photo-chemical decomposition of benzidine in different halomethane solvents in addition to the corresponding UV absorption spectra and fluorescence emission spectra are discussed. The photochemical quantum yields (phiC lambda ex = 254 nm) of benzidine in halomethanes is dependent upon the halogen content in the solvent. This effect may be explained by the assumption that free radicals are formed during photolysis of these solvents followed by the abstraction of electrons from a benzidine molecule forming macroradicals of the latter. Both mono- and di-radical benzidine cations have been detected by different techniques. The well known electron absorption peak at 283 nm is characteristic of neutral benzidine while those observed at ca. 370 and 565 nm are assigned to the blue-monoradical cation and yellow-diradical cation, respectively. The blue-monoradical cation has been isolated after irradiation as a blue precipitate. A comparison between neutral benzidine and the blue monoradical cation are made using both IR and differential thermal analysis (DTA) techniques. The fluorescence quenching of solutions of benzidine in inert solvents using halomethanes have been studied. The results obtained are interpreted in terms of a diffusional quenching mechanism.     

Nitric oxide adsorbed on zeolites: EPR studies

CW-EPR studies of NO adsorbed on sodium ion-exchanged zeolites were focused on the geometrical structure of NO monoradical and (NO)2 biradical formed on zeolites. The EPR spectrum of NO monoradical adsorbed on zeolite can be characterized by the three different g-tensor components and the resolved y-component hyperfine coupling with the 14N nucleus. Among the g-tensor components, the value of g(zz) is very sensitive to the local environment of zeolite and becomes a measure of the electrostatic field in zeolite. The temperature dependence of the g-tensor demonstrated the presence of two states of the Na-NO adduct, in rigid and rotational states. The EPR spectra of NO adsorbed on alkaline metal ion-exchanged zeolite and their temperature dependency are essentially the same as that on sodium ion-exchanged zeolite. On the other hand, for NO adsorbed on copper ion-exchanged zeolite it is known that the magnetic interaction between NO molecule and paramagnetic copper ion are observable in the spectra recorded at low temperature. The signals assigned to (NO)2 biradical were detected for EPR spectrum of NO adsorbed on Na-LTA. CW-EPR spectra as well as their theoretical calculation suggested that the two NO molecules are aligned along their N-O bond axes. A new procedure for automatical EPR simulation is described which makes it possible to analyze EPR spectrum easily. In the last part of this paper, some instances when other nitrogen oxides were used as a probe molecule to characterize the zeolite structure, chemical properties of zeolites, and dynamics of small molecules were described on the basis of selected literature data reported recently.     

1,2-和1,4-萘醌248 nm激光光解的瞬态吸收光谱研究

利用纳秒级激光光解动态吸收光谱装置,研究了1,2-和1,4-萘醌中性水溶液的瞬态吸收光谱.发现1,2-萘醌及1,4-萘醌被光电离后形成的阳离子自由基在380nm均有最大吸收,但1,4-萘醌阳离子自由基在衰变过程中又形成了两种新的活性粒子,它们的最大吸收分别位于410和580nm,分析表明:410nm属于1,4-萘醌脱氢自由基的吸收,而580nm很可能归属由于电子转移而形成的瞬态产物.进一步研究发现,1,2-萘醌在中性水溶液中能被248nm激光单光子电离.     

Factors affecting the selection of products from a photochemically generated singlet biradical

The chemistries of a monoradical of the ultrafast "radical-clock" type and a structurally related singlet biradical, generated by Norrish type II photochemistry, are compared. The monoradical is found to undergo the characteristic ring-opening reaction of its class at about 10(10) s(-1) at room temperature. However, the singlet biradical shows no evidence of the analogous ring-opening reaction. The contrasting chemistry is traced not to a fundamental difference in electronic structure of the two intermediates, but rather to a steric interaction that the biradical alone would have to suffer during the ring opening. Although the magnitude of the steric hindrance is small (estimated 15-20 kJ mol(-1)), it is enough to shut down the reaction, because the biradical has other facile product-forming reactions available.     

A stable organic triradical with truncated π-conjugation as a model for single-component organic molecule-based ferrimagnetics

As a novel molecular design for genuinely organic molecule-based ferrimagnets, we have proposed a strategy of ‘single-component ferrimagnetics.’ When a π-biradical with an S=1 ground state and a π-monoradical with S=1/2 are united by σ-bonds, the π-conjugation between the biradical and the monoradical moieties should be truncated in the resultant triradical. This gives magnetic degrees of freedom for both S=1 and S=1/2 in the single molecule, serving as a building block for organic molecular ferrimagnets. We have designed and synthesized a triradical, 2,2,6,6-tetramethyl-pipelidine-1-N-oxyl-4-carboxylic acid 2,4-bis(1-oxyl-3-oxido-4,4,5,5-tetramethyl-2-imidazolin-2-yl)-phenyl ester (2) as a model compound for single-component ferrimagnetics. Solution-phase ESR spectra from 2 are explained by a perturbation treatment assuming that the exchange interaction within the biradical moiety is much larger than those between the biradical and the monoradical moieties, which is suitable for single-component ferrimagnetics. From susceptibility measurements for a cyclohexane-substituted biradical, cyclohexane carboxylic acid 2,4-bis(1-oxyl-3-oxido-4,4,5,5-tetramethyl-2-imidazolin-2-yl) phenyl ester (4) as a biradical analogue of 2, it is shown that the intramolecular ferromagnetic interaction has been found to be unaffected by the chemical modification for anchoring the monoradical moiety.     

Transient absorption spectra and dynamics of InSe nanoparticles

Time-resolved fluorescence and transient absorption results have been obtained for small (approximately 3 nm) and large (approximately 5-8 nm) InSe nanoparticles in room-temperature solutions. The large particles are nonfluorescent, indicating that the conduction band is at M and the optical transition is forbidden. For some fraction of the small particles, the bottom of the conduction band is at Gamma and the optical transition is allowed. The small particle fluorescence measurements indicate that hole trapping occurs on the 200-300 ps time scale. The transient absorption spectra are featureless throughout the visible with a broad maximum at 600-650 nm. The transient absorption kinetics of both small and large particles show a 200-300 ps decay component that is assigned to hole trapping. These kinetics also show a 15 ps decay that has a larger amplitude in the case of the large particles and is assigned to an electron Gamma to M relaxation. The amplitude of this decay indicates that the initial electron and hole intraband transitions result in roughly comparable intensities of the initial transient absorption.     

ACTION SPECTRA FOR ACCUMULATION OF INORGANIC CARBON IN THE CYANOBACTERIUM, Anabaena variabilis

Abstract— Action spectra for accumulation of inorganic carbon were obtained for Anabaena variabilis , strainM–2, in the presence and absence of photosynthetic CO₂ fixation. The action spectrum for inorganic carbon accumulation in the presence of CO₂ fixation showed a peak around 684 nm, corresponding to chlorophyll a absorption in PS 1, while that for CO₂ fixation showed a peak around 630 nm, corresponding to phycocyanin absorption in PS 2. The action spectra obtained in the presence of iodoacetamide or diuron, which inhibit CO₂ fixation, showed two peaks, one at about 684 nm and the other at 630 nm, with the 630 nm peak height 80 to 90% of the 684 nm peak. These results indicate that inorganic carbon transport in A. variabilis can be driven with near equal efficiency by energy derived from absorption in photosystem 1 alone and with energy transferred to PS 1 after absorption by PS 2.     

Preparation of new photosensitive Nb2O5 gel films modified with benzoylacetone and properties of heat-treated films

In this study, in order to develop a new photosensitive gel film, Nb₂O₅ gel films including a chelate ring were prepared by the sol?Cgel method. Photosensitive and patterning properties of the gel films were investigated. Properties such as refractive index for annealed films were also evaluated. In the electronic absorption spectra of the gel films, the absorption peak assigned a chelate ring was observed at 353?nm, this peak intensity decreased by UV irradiation. From this result, the obtained gel films exhibit photosensitivity. Fine patterns (minimal width of about 2???m) could be fabricated. It was found that the value of refractive index reaches a maximum of 2.25 for the film heat-treated at 800?°C.     

Exchange interaction in covalently bonded biradical-monoradical composite molecules

As a novel molecular designing for genuinely organic molecule-based ferrimagnets, we have proposed a strategy of "single-component ferrimagnetics". When a pi-biradical with an S = 1 ground state and a pi-monoradical with S = (1)/(2) are united by sigma-bonds, the pi-conjugation between the biradical and the monoradical moieties should be truncated in the resultant triradical. This gives magnetic degrees of freedom for both S = 1 and (1)/(2) in the single molecule, serving as a building block for organic molecule-based ferrimagnets under favorable conditions (single-component ferrimagnetics). We have designed and synthesized a triradical, 3-(1'-oxyl-3'-oxido-4',4',5',5'-tetramethylimidazolin-2-yl)benzoic acid 2,4-bis(1' '-oxyl-3' '-oxido-4' ',4' ',5' ',5' '-tetramethylimidazolin-2-yl)phenyl ester (4), as a model compound for the novel approach to genuinely organic ferrimagnets. In the triradical 4, a m-phenylene-bis(nitronyl nitroxide) biradical with a triplet (S = 1) ground state is united with a phenyl nitronyl nitroxide monoradical (S = (1)/(2)) by an ester coupler. Solution-phase ESR spectra from 4 exhibited a complex hyperfine splitting due to (14)N and (1)H nuclei. The analysis of the hyperfine structure based on perturbation calculations has revealed that the exchange interaction within the biradical moiety is much larger than those between the biradical and the monoradical moieties and the magnetic degrees of freedom for both S = 1 and (1)/(2) are retained in 4. An X-ray crystal structure analysis showed that the triradical molecules are arranged in a one-dimensional molecular chain in the crystal. The magnetic susceptibility in a crystalline solid state is consistent with the crystal structure.     

Pulse radiolysis of methylene blue and toluidine blue in PVA

Pulse radiolysis experiments were carried out with aqueous solutions of thionine dye methylene blue (MB) and toluidine blue in the presence of polyvinyl alcohol. The transient spectra obtained show maxima at 400 and 880 nm and are assigned to the respective semiquinone radical anions. The semiquinone radical decayed by a second order process. Furthermore, MB in PVA films were bleached by γ-radiolysis and the change in absorption was found to be linear with the dose.     

Different molecular constituents in pheomelanin are responsible for emission, transient absorption and oxygen photoconsumption

Steady-state absorption and emission spectroscopies, oxygen activation and transient spectroscopy on a single sample of synthetic pheomelanin are compared. The absorption, emission and excitation spectra of pheomelanin depend on the molecular weight (MW) of the dissolved pigment constituents. While weakly-depending on MW, the maximum of the emission excitation spectrum is approximately 400 nm. The electron paramagnetic resonance oximetry measurements show a clear increase in oxygen uptake between 338 and 323 nm, and also reveal a local enhancement around approximately 370 nm. Pump-probe absorption spectroscopy reveals that photoexcitation of pheomelanin by UVA light generates a transient absorption peak in the visible and UV regions within the instrument response. The action spectrum for the formation of the 780 nm transient species peaks at approximately 360 nm. While both transient absorption bands show the same ultrafast decay component, the 780 nm peak completely vanishes on the 10s of picosecond time scale, but the UV band shows a kinetic evolution to a subsequent intermediate. While in a similar wavelength range, the maximum of the action spectrum derived from the transient data, the emission excitation spectrum and the action spectrum for photoconsumption all differ from one another, suggesting that the chromophore responsible for each is not that same. This raises concern about comparing the results from different photochemical methodologies for melanin, which is a specific case of comparing data on systems where molecular constituents are not well defined.     

Absorption spectra of viral components of Sendai virus in the wavelength region from 130 to 320 nm.

Using synchrotron radiation as a light source, the absorption spectra of purified viral components of the Sendai virus, i.e. messenger RNA, lipids, spike (envelope) proteins, reconstructed envelopes, core proteins and whole virions, were obtained in the wavelength region 130-320 nm by measuring the transmission of thin films. Viral (messenger) RNA two peaks at 260 and 190 nm, and a large increase below 160 nm. The absorption spectrum of lipids exhibited a broad peak at 190 nm and a very sharp increase below 160 nm. With spike proteins, a slight peak at 280 nm and a shoulder at 230 nm were observed in addition to a sharper peak at 190 nm and a rather slow increasing absorption below 160 nm. Reconstructed envelopes showed the features of a combination of lipids and proteins. The absorption spectra of core proteins and whole virions exhibited similar characteristics to spike proteins. Conventional UV data were also obtained in the wavelength range 210-320 nm with RNA and lipids. The UV and synchrotron radiation data were in good agreement in terms of the mass absorption coefficients. The molecular splitting of spike proteins was also examined. Proteins gave more diffuse reflection than their subunits, causing a reduction in absorption. This was explained by a loss of transparency with increasing molecular weight.     

3,5-二氯水杨醛缩邻苯二胺铜配合物的合成、晶体结构及光谱学性质

合成了3,5-二氯水杨醛缩邻苯二胺铜配合物[Cu(C₂₀H₁₀Cl₄O₂N₂)]·DMF。 通过元素分析、红外光谱、热重测试技术对其进行了表征,同时用X射线单晶衍射确定了其晶体结构;利用紫外-可见光吸收光谱、荧光激发和发射光谱研究了该配合物的光物理性能。 结果表明,该晶体属于单斜晶系,空间群为P2(1)/n,a=0.81316(8) nm,b=1.53101(18) nm,c=1.87819(19) nm,β=92.4530(10)°,Z=4,最终偏差因子R₁=0.0584,ωR₂=0.1482,配合物的中心铜离子与席夫碱的2个O和2个N配位,形成1个五元环和2个六元环,从而构成了1个四配位的平面构型;配合物的热分解温度为384 ℃,具有很好的热稳定性;在DMF溶液体系中,配合物的荧光激发带位于360～480 nm,荧光发射峰在507 nm处,为蓝绿色荧光,最佳激发波长为440 nm,禁带宽度2.59 eV。     

Influence of bond lengths between substituents and mother molecule on spectral properties of pyrazoloquinolines

Absorption and luminescent spectra of several new synthesized pyrazolo-quinoline possessing different substituents are studied. Absorption spectra of all the considered compounds possess five relatively strong absorption bands at about 430, 320, 270, 253 and about 230 nm. A correlation between the bond lengths between the substituent molecule and mother molecule with the observed spectral shifts was found. Theoretical spectra obtained within semi-empirical quantum chemical AM1 calculation methods seem to be more widened compared to the experimental ones due to electron-vibration interactions. However generally a good coincidence between spectral positions between experimental and calculated spectral peak positions was achieved. The corresponding experimental spectra have an absorption edges situated at about 430 nm which appears in fairly good agreement with quantum chemical simulations, namely for absorption spectra calculated by semi-empirical AM1-method. The red shifts in the experimental luminescence spectra are a consequence of electron-vibration interactions which increase with the effective radius and polarizabilities of the particular substituents.     

Time-resolved spectroscopic studies on phenyl-substituted poly(phenylenevinylene)s by picosecond excite- and probe technique

Photoinduced picosecond absorption spectra of poly(1,4-phenylene-1,2-diphenylvinylene) (DP-PPV) and of related oligomeric and polymeric compounds were investigated in toluene solution. Between 400 and 900 nm the rise (5 … 40 ps) and decay (40 … 300 ps) of three transient absorption bands have been observed. The low energy absorption appears with a time delay of 5 ps and has its peak at 680 nm (1.8 eV). This band position is coincident with the well known ECS radical ion (polaron) absorption and is therefore assigned to this type of photogenerated charged species. The other two absorptions appear at higher energies. One of them is situated at 2.8 eV which is near to the band edge (2.9 eV). It originates immediately with the exciting pulse and is attributed to a neutral excited state. The other one (2.7 eV) is suggested to be due to an ECS diion (bipolaron).     

Laser induced transient absorption in liquid pyrene

The transient absorption spectra, over the spectral range 430 to 1020 nm, are presented for pure liquid pyrene at 425°K. The absorption profiles show both short- and long-lived components. The long-lived transient has a lifetime much greater than the lifetime of the monitoring flash-lamp pulse, and it is suggested that this absorption can be assigned to the triplet state of the monomer. The short-lived component is unassigned.     

Absorption spectroscopic and FTIR studies on EDA complexes between TNT (2,4,6-trinitrotoluene) with amines in DMSO and determination of the vertical electron affinity of TNT

TNT (2,4,6-trinitrotoluene) formed deep red 1:1 CT complexes with chromogenic agents like isopropylamine, ethylenediamine, bis(3-aminopropyl)amine and tetraethylenepentamine in DMSO. The complexes were also observed in solvents like methanol, acetone, etc. when the amines were present in large excess. The isopropylamine, complex showed three absorption peaks (at 378, 532 and 629 nm) whereas higher amines showed four peaks (at 370, 463, 532 and 629 nm). The peak at 463 nm vanished rapidly. The peak of the complexes near 530 nm required about 8-10 min to develop and the complexes were stable for about an hour but the peak slowly shifted towards 500 nm and the complexes were found to be stable for more than 24 h. The evidence of complex formation was obtained from distinct spots in HPTLC plates and from the shifts in frequencies and formation of new peaks in FTIR spectra. The peaks near 460 nm (transient) and 530 nm may be due to Janovsky reaction but could not be established. The extinction coefficients of the complexes were determined directly which enabled the accurate determination of the association constants KDA with TNT and amines in stoichiometric ratios. The results were verified using iterative method. The quantification of TNT was made using epsilon value of the complex with ethylenediamine. The vertical electron affinity (EA) of TNT was calculated using the method suggested by Mulliken.     

Diffuse-reflectance laser flash photolysis of 16-(1-pyrene)-hexadecanoic acid adsorbed on silica

The absorption and fluorescence of 16-(1-pyrene)-hexadecanoicacid adsorbed on silica have been investigated. Time-resolved transient diffuse reflectance spectra were recorded following pulsed nanosecond laser excitation at 355 nm of pyrene, 1-methylpyrene and 16-(1-pyrene)-hexadecanoicacid adsorbed on silica. In addition to a rapidly decaying transient, absorbing at 420 nm assigned as the triplet state, and of the radical cation, absorbing at 460 nm, another long living transient species absorbing at 420 nm was observed for 16-(1-pyrene)-hexadecanoic acid. The decay is reversible but complete recovery takes several hours. Although no definitive assignment could be made for this transient several possibilities are discussed. The radical cations of the investigated molecules are formed by a biphotonic process. The non-exponential decay of the radical cations could be analyzed in the framework of a Gaussian distribution of free energy barriers.