Benzene photophysical data

Table 4 presents comprehensive photophysical data of 2T-7T (di-n-butyl), including singlet oxygen quantum yields (4>a) in benzene. Considering the absorption and emission spectra, there is a relatively small effect of solvent on these maxima. In the fluorescence excitation spectra, there is a considerable red shift, 1600 cm-1, in the maxima with an excellent linear correlation between 1/n and the maximum of the first transition, as well as the 0-0 energy particularly for 4T-7T. 

Data taken from Ref. [60], The structures and photophysical data for many of these molecules can be found in Chap. 4 In ethanol solution In cyclohexane solution ° l,4-bis(5-phenyloxazol-2-yl) benzene... 

A brief review and reassessment of data on the photophysics of benzene has been presented by Pereira. Evidence for the l E2g valence state has been obtained by u.v. two-photon spectroscopy.Slow electron impact excites fluorescence in thin films of benzene at 77 K as well as emission from isomers." The fluorescence yields and quenching by chloroform of alkyl-benzenes and 1-methylnaphthalene after excitation into Si, Sz, and S3 states and after photoionization have been measured. The channel-three process has been reconsidered in terms of the effects of local modes and Morse oscillator potentials. Excited-state dipole moments of some monosubstituted benzenes have been estimated from solvent effects on electronic absorption spectra, Structural imperfections influence the photochemistry of durene in crystals at low temperatures. Relaxation time studies on excited oxido-substituted p-oligophenylenes have been made by fluorescence depolarization... 

A large amount of spectroscopic data are now available for benzene, providing much information on photophysics and photochemistry properties of the lowest excited states of this molecule. Nevertheless the nature of the various radiative and nonradiative transitions involved in the deexcitation of the first excited states is far from being completely understood. 

Much experimental evidence is available on the small solvent shifts which are measureable but, since little effect on the photophysical decay processes is expected, no review of this work will be attempted the reader is referred to the work of Eastman and Rehfeld (70) who report data for benzene in the vapor phase and in 37 different solvents. 

Influence in extension of chromophore conjugation on TPA was studied for the fluorinated polyenes 1-3. Pentafluorosubstitution reduces re-electron density at the left aromatic benzene ring. This results in an electron-deficient substituted benzene with a re-electron density comparable with that of cyanobenzene [341]. This was concluded from the reduction potentials of 1,2,4,5-tetrafluorobenzene (El = -2.4 V vs. SCE [342]) and cyanobenzene = -2.3 V vs. SCE [341]). The larger re-conjugation in 3 causes an increase of e compared to 1 but the change of A/i()] was rather modest compared to the increased size of the chromophore [224]. TPA data and representative photophysical parameters are summarized in Table 3.1. 

Simple benzenoid systems have not been as extensively reported as in previous years. West and Miller have studied the fluorescence from dilute solutions of benzene in cyclohexane induced by protons and alpha particles. A model for interpretation of the data involving intratrack quenching by products of the irradiation is not fully adequate. Gibson and Rest have measured quantum yields of fluorescence and phosphorescence in various frozen gas matrices and from these yields and lifetime data have calculated the photophysical rate constants for and at 12 K, which are given in Tables 1, 2, and 3. The... 

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