Ultraviolet fluorescence spectra

Hancock and coworicers have studied the photochemistry of a series of compounds in which the -B=N- functional group is the essential chromophore " The -B=N- linkage in aminoboranes is analogous to the isoelectronic (-C=C-) ethylenic linkage in molecules studied extensively by organic photochemists. Many aminoboranes absorb radiation in the near ultraviolet Fluorescence spectra have been reported for a number of compounds with the general formula... 

The unmodified form of coelenterazine, C26H2i03N3(mass spec. M+ 423), can be crystallized from methanol as orange-yellow prisms with a melting point of 175-178°C (dec). In methanol, coelenterazine is fluorescent in yellow, and its ultraviolet absorption spectrum shows a maximum at 435 nm (s 9,800), as shown in Fig. 5.1. 

A number of investigations of the copper-group oxides and dioxygen complexes have been reported. The electronic spectra of CuO, AgO, and AuO were recorded in rare-gas matrices (9), and it was found that the three oxides could be formed effectively by cocondensation of the metal atoms with a dilute, oxygen matrix, followed by near-ultraviolet excitation. The effective wavelengths for CuO or AgO formation were X > 300 nm and for AuO was X > 200 nm. In addition, the laser fluorescence spectrum of CuO in solid Ar has been recorded (97). 

Photophysical Processes in Dimethyl 4,4 -Biphenyldicarboxy-late (4,4I-BPDC). The ultraviolet absorption spectrum of dimethyl 4,4 -biphenyldicarboxyl ate was examined in both HFIP and 95% ethanol. In each case two distinct absorption maxima were recorded, an intense absorption near 200 nm and a slightly less intense absorption near 280 nm. The corrected fluorescence excitation and emission spectra of 4,4 -BPDC in HFIP at 298°K shows a single broad excitation band centered at 280 nm with a corresponding broad structureless emission band centered at 340 nm. At 77°K, the uncorrected phosphorescence spectra shows a single broad structureless excitation band centered at 298 nm, and a structured emission band having maxima at 472 and 505 nm with a lifetime, t, equal to 1.2 seconds. 

In addition to a fluorescence perturbation, the Cd(II)-5d combination also uniquely yields aperturbation in the ultraviolet (UV) spectrum. A difference spectrum obtained by subtracting a fractional amount of an uncomplexed 5d spectrum from the perturbed spectrum is the mirror image of a fluorescence difference spectrum obtained by similar means. Moreover, excitation at 400 nm (where 1-4 are weakly absorbing but where moderate absorption is seen in the difference spectrum) gives rise to an emission spectrum with identical shape and Amax (456 nm) to that of the fluorescence difference spectrum. Thus, evidence points to the existence of two equilibrating ground state species as the physical basis for the chelatoselective emission. Bouas-Laurent has reported a related observation in methanol where a red-shifted CHEF was observed for a T1(I) 7r-complex.(14)... 

The primary process in the vacuum ultraviolet photolysis of methylene iodide has been studied by Style and Ward,12 who observed that irradiation with light of wavelength 1250-2000 A. excites the fluorescence spectrum of iodine. Attempts to observe any appreciable delay between light absorption and fluorescence were unsuccessful, and the intensity of fluorescence was directly proportional to the light intensity and the pressure of methylene iodide. It was concluded that the excited I2 was produced in the primary process,... 

In Fig. 7 an average of twenty transients similar to that in Fig. 6 is presented. The curves were matched by the procedure described above and are displayed as the sum of all 20 curves. Once again the curves are offset for reasons of clarity. The signal-to-noise ratio is dramatically improved by this procedure. Even so, the wavelength dependence of the fluorescence decay time remains a subtle effect. Obviously, one must bias the data on the ultraviolet tail of the fluorescence spectrum relative to the fluorescence maximum near 360 nm in order to bring out this effect more clearly. 

Once laid, the polystyrene films were further purified by exhaustive extraction with methanol or n-heptane the progress of extraction was followed by the ultraviolet spectra of the extracts. These preirradiation extractions showed considerable variation in purity among the three polystyrenes in spite of reprecipitation measures. The degree to which solvents can remain with a 20/ film is suggested by the need of seven days of continuous methanol or n-heptane extraction to remove all of the extractable benzene from a film laid from that solvent and dried in vacuum at 65°C. for 24 hours. For film laid from methylene chloride, an optically clean n-heptane extract was obtained from the AIBN-ini-tiated sample within a few hours, but up to 48 hours were required for the benzoyl peroxide-initiated samples. The extracted 20/ polystyrene films were essentially non-absorbing above 285 m/, no absorption attributable to material other than polystyrene could be observed, and only one peak (337 m/ ) was seen in the fluorescence spectrum in methylene chloride. Once the films were purified by extraction, the products and wettability changes resulting from irradiation were the same for all polystyrene samples and were independent of the solvent from which the films were laid. 

A series of policyclic oxazole derivatives, analogous to compound 124, were synthesised in order to verify their fluorescence properties <07EJO3613>. The oxazole VUV (vacuum ultraviolet) absorption spectrum over the range 5-12 eV was analyzed <07CP154>. New jr-conjugated polymers containing oxazole in the main chain were synthesised and their optical and electrochemical properties analyzed <07P2331>. 

The longest wavelength band in the ultraviolet (UV) spectrum of the 1 -phenyl-fV-methyl derivative of 9 was reported to occur at 356 nm in cyclohexane and displayed only slight solvatochromism, while the fluorescence spectrum ( = 0.13, cyclohexane) showed marked solvatochromism, for example, 87 nm with a change from cyclohexane to dimethylforma-mide (DMF) <1995CC1249>. No infrared (IR) data have been reported recently for borepins or their analogues. 

The photochemistry of carbon disulfide has been studied in only moderate detail. It has long been interesting to spectro-scopists because of the complexity of its near ultraviolet absorption spectrum and the fact that its radiative lifetime is substantially longer than that expected on the basis of integrated oscillator strengths. Its fluorescence has been observed whereas that of the two other analogous 16 valence-electron molecules,... 

Ultraviolet A spectrum Fluorescent black lights Fluorescent PUVA lights... 

Ultraviolet B spectrum Fluorescent sunlamp Mercury halide lamp without a filter Sunlight... 

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