Excimer fluorescence, compounds quantum yields

To determine whether QD mid QD/QM for the intramolecular excimer differ from the corresponding inteimolecular values, the fluorescence behavior of excimer-forming bis(2-naphthyl) compounds has been collected in Table 9. The experimentally-measured excimer and monomer quantum yields [Pg.64]

While the photodimerization of bis(l-naphthylmethyl) ether was acknowledged somewhat earlier 39), the photodimers were first characterized and the quantum yield of the dimerization determined by Todesco et al. U2). Both the syn- and anti-photodimers were formed in roughly equal amounts, and the quantum yield for formation of the anti-dimer was independent of solvent. However, the quantum yields for formation of the syn-dimer and for excimer fluorescence were found to vary with solvent such that their sum was independent of solvent. The fact that irradiation of l,3-bis(l-naphthyl)-1-propanol yields only the syn-photodimer 113> indicates that the conformational properties of oxygen are largely responsible for anii-dimerization in the ether compound. The possibility of photodimerization was unfortunately not considered in the fluorescence studies of protonated bis (1-naphthylmethyl) amine 115>, l,3-bis(4-methoxy-l-naphthyl) propane 116>, and meso-bis( 1 -(1 -naphthyl-ethyl) ether 13). 

The quantum yields and decay rates of the intermolecular excimer of naphthalene and its derivatives are given in Table 8. The solvent ethanol water 95 5 v/v is one of the few solvents in which the fluorescence of these compounds has been completely characterized. Examination of the values of kD and QM for other solvents shows that 95 % EtOH does not belong in the same class as the hydrocarbon solvents, or even anhydrous ethahol. In the latter solvents, kD/kM falls between 0.8 for 1,6-dimethylnaphthalene and 1.4 for naphthalene. Although the quantity k /k has been measured only once for a naphthyl compound in a hydrocarbon solvent (see Table 5), the values 0.3 and 0.4 seem appropriate for 1,6-dimethylnaphthalene and naphthalene, respectively, in hydrocarbon solvents. Since QD/QM = (kpD/kpM) -s-(kD/kM), we obtain QD/QM = 0.4 for 1,6-dimethylnaphthalene and 0.3 for naphthalene. The intrinsic quantum yield ratio as determined in 95 % EtOH solvent is about seven... 

The excited state properties of bis-a-9-anthrylmethyl ethers 23 closely resemble those of l,3-di-9-anthrylpropane derivatives. The photoexcited parent compound 23a deactivates by fluorescence (0 = 0.03) from the locally excited state only, and it isomerizes by intramolecular 4ji+4ji cycloaddition with a quantum yield of 0.32 [66]. By contrast, excimer emission (see Table 4) does characterize the excited state properties of the 10,10 -diphenyl derivative 23b, which does not undergo intramolecular cycloaddition for steric reasons [66,67]. 

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