Quantum yields intrinsic

Another feature of the simplest model that needs modification is the assumption of a fixed dipole amplitude. Because of the efficient capture of nonpropagating near fields by a surface, a fixed-amplitude dipole emits more power, the closer it moves to a surface. However, in steady-state fluorescence, the emitted power can only be as large as the (constant) absorbed power (or less, if the intrinsic quantum yield of the isolated fluorophore is less than 100%). Therefore, the fluorophore must be modeled as a constant -power (and variable-amplitude) dipole. Many of the earlier theoretical references listed above deal only with constant-amplitude dipoles, so their results must be considered to be an approximation. 

The two above features which modify the simplest theory extend the range of distances z between the fluorophore and the surface over which the results remain valid, from a minimum of several hundred nanometers without the modifications to less than ten nanometers with them. Those two features are incorporated into the results displayed here. Other refinements, not included here, involve consideration of energy transfer to electron-hole pairs (for metals only at z < 10 nm) and nonhomogeneous atomic field effects (z<0.25 nm). We first assume that the intrinsic quantum yield is 100% then we will modify that assumption. 

The fluorescence of liquid alkanes is supposed to originate entirely from the relaxed Si state. Walter and Lipsky [154], by measuring the fluorescence yields of alkane solutions irradiated with 165 nm photons or Kr beta particles ( niax = 0-67 MeV) relative to benzene fluorescence, determined the following yields 2.3-dimethylbutane G Si) < 1.3, cyclohexane 1.4-1.7, methylcyclohexane 1.9-2.2, dodecane 3.3-3.9, hexadecane 3.3-3.9, d5-decalin 3.4, and bicyclohexyl 3.5. After reinvestigating the intrinsic quantum yield of cyclohexane fluorescence, Choi et al. published G(5 i) = 1.45 for this alkane in Ref. 155. For tra 5-decalin a G Si) value of 2.8-3.1 has been accepted [65,128,132]. The uncertainties in the values reflect the uncertainties in the intrinsic fluorescence quantum yields. 

The lifetime of monomer fluorescence in the absence of routes to excimer formation is tm = (kFM + koM + kTM) 1 = ky1, and the intrinsic quantum yield is Qm = kpM/kM. The lifetime and intrinsic quantum yield of excimer fluorescence, td and Qd, will be considered in a later section. 

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... 

Table 8. Decay Rates and Intrinsic Quantum Yields of Naphthalene Compounds in Solution at Room Temperature...

In summary, the intrinsic quantum yield and lifetime of the 2-naphthyl excimer is not significantly affected by the mode (intra vs. inter) of excimer formation, at least in a nonpolar solvent. The next question to be pursued is whether the similarity between intra- and intermolecular excimers is maintained in a rigid matrix. 

The intrinsic quantum yield of monomer fluorescence QM for the polymer is the same as for the monochromophoric model compound. QM in air-equilibrated rigid hosts is the same as in degassed hydrocarbon solvents, and is independent of the host matrix in rigid systems. 

Luminescence properties (lifetimes and intrinsic quantum yields) of Ndnl f)-diketonates with dbm derivatives (ro(Nd) = 0.25 ms)... 

Intrinsic quantum yields (0[ ) estimated from a radiative lifetime to(Nd) = 0.8 ms. intrinsic quantum yields (Q j ) estimated from a radiative lifetime tq (Nd) = 0.27 ms. 

Intrinsic quantum yields (Oj ) estimated from a radiative lifetime Tq(Er) = 8 ms. 

The attachment point of the antenna is indicated by — in case of ternary complexes, the sketched molecule acts both as the ternary ligand and antenna. Intrinsic quantum yields estimated from a radiative lifetime ro(Yb) = 2 ms. 

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