Anthracene triplet, spectrum

A flasn spectrum of anthracene triplets at various delay times are given in Figure 10.11. 

Figure 10.11 clash spectrum of anthracene triplet at different delaytimes. 

In the presence of anthracene (which has an energetically lower triplet state than fluoranthene or 10-methyl-phenothiazine), the ECL emission is shifted from the broad maximum at ca. 450 nm to the characteristic anthracene fluorescence spectrum with the three maxima at 390, 410 and 445 nm. 

Examination of DABA photolysis in cyclohexane instead of benzene solution leads to predictably different results. The laser spectroscopy shows that 3BA is formed but, in this solvent, the triplet carbene undergoes an additional rapid reaction to generate the mesitylbora-anthryl radical (BAH ). This radical is identified by comparison of its spectrum with that of an authentic sample prepared from dihydrobora-anthracene. The half-life of... 

Fig. 13. Triplet-triplet absorption spectrum of anthracene recorded in plexiglas at room temperature (From Wild, Ref. ))...

Parker and Joyce125 have also observed a new band in the delayed emission spectrum of solutions of anthracene (A) and 9,10-diphenylanthracene (B) in ethanol at — 75°C, which they attribute to the exciplex of these species formed in the process of mixed triplet-triplet annihilation... 

No difference in the absorption spectrum is observed. The lifetimes of the two fluorescence emissions are both of the order of 10-8 sec. Another effect has been observed with hydrocarbons both as vapor and in solution, namely, a "delayed fluorescence emission with a life of a few milliseconds (56,63). This was at first interpreted as process 9, and the term excimer applied to the hypothetical excited dimer. However, C. A. Parker and C. G. Hatchard have shown that the intensity of the delayed fluorescence, which has the same spectrum as that from the excited singlet molecule, depends upon the square of the intensity of the exciting light (49). The mean life of the delayed fluorescence of anthracene solutions is (about) one-half that of the triplet state, and the effect is not observed in rigid media. These facts show that the delayed emission must be caused by an interaction between two triplet-state molecules ... 

Figure 3-25 Resonance Raman spectra of canthaxanthin in the So and T states. Spectra were obtained with the vidicon spectrograph by using 555 nm probe wavelength and optical excitation of anthracene (at 355 nm) for triplet production. Trace a , groundstate spectrum, no 355 nm excitation pulse trace b , superposition of So and T spectra trace c , T spectrum, obtained by approximately normalized subtraction of trace a from trace b . Three different vidicon frames (along the frequency axis) are shown intensities are not to scale. The solid line is obtained by an 11-point quartic running smooth of the observed points. The negative base line excursions denoted by the vertical arrows are OMA artifacts. (Reproduced with permission from Ref. 82. Copyright 1981 American Chemical Society.)...

An observation of the triplet state of anthracene in benzene (27) is of special interest in that, in addition to the absorption spectrum of the triplet, a delayed fluorescence emission from the singlet at 4300 A. was recorded. The intensity of fluorescence, which was approximately proportional to the square of the triplet concentration at all times, was attributed to triplet-triplet quenching ... 

Nanosecond Flash Photolysis Measurements.—A computer-controlled ns flash photolysis spectrometer has been described. " The system was employed in a study of the photochemistry of xanthene dyes in solution. A nitrogen laser was used to provide 2—3 mJ excitation pulses at 337.1 nm for a ns flash photolysis study of electron-transfer reactions of phenolate ions with aromatic carbonyl triplets. " A PDP II computer was used to control the transient digitizer employed for detection, and to subsequently process the data. A nanosecond transient absorption spectrophotometer has been constructed using a tunable dye laser in a pulse-probe conflguration with up to 100 ns probe delayA method for reconstructing the time-resolved transient absorption was discussed and results presented for anthracene in acetonitrile solution. The time-resolution of ns flash photolysis may be greatly increased by consideration of the integral under the transient absorption spectrum. Decay times comparable to or shorter than the excitation flash may be determined by this method. 

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