Phosphorescence of naphthalene

Photoreticulation of polyvinylbenzophenone is efficiently inhibited by naphthalene which acts as a quencher of the excited triplet state of the aromatic carbonyl group [65]. The efficiency of this energy transfer at 77°K has been studied quantitatively by measuring the decrease in the phosphorescence of polyvinylbenzophenone or the increase in the phosphorescence of naphthalene as a function of additive concentration. The results demonstrate that in this polymer an extensive energy migration occurs prior to the transfer [66]. 

Excitation of benzophenone in solid solution at 77K with light of wavelength 366nm produces phosphorescence. As naphthalene is added, the... 

Fig. 9. Decay of luminescence with time. Ordinate In (luminescence intensity) one division = 0.25. Abscissa time one division = 0.0003 sec. for curves (a) and (6) 0.0005 sec. for curve (c) 1.0 sec. for curve (d) and 0.1 sec. for curve (e). (a) and (6) Delayed fluorescence of pyrene monomer and dimer in ethanol at +23°C. (c) Delayed fluorescence of naphthalene in ethanol at —23°C. (d) Triplet-singlet phosphorescence of 10-W phenanthrene in EPA at 77°K. (e) Delayed fluorescence of 10-lAf phenanthrene in EPA at 77°K.

Hutchison reported the first ESR spectrum of a metastable phosphorescent state by study of naphthalene oriented in durene crystals.4 Since then, similar spectra have been recorded for several other polynuclear aromatics both oriented in host crystals and randomly suspended in glassy matrices. D values for all these ir,n excited states are quite low, indicating little interaction between the unpaired electrons. Interestingly, D for the quinolines equals 0.10cm"1 just as in naphthalene,197 indicating that the presence of a heteroatom does not necessarily change the ir,w nature of the lowest triplet state very much. A similar conclusion has been reached from a comparison of the ESR spectra of fluorene, carbazole, dibenzofuran, and dibenzothiophene.198... 

The observed quenching effects suggest that the excitation energy of the reactive triplet may be close to the 71 kcal Zimmerman estimated from the phosphorescence spectrum of 35. On the other hand, lumi-santonin, also an enone, must have a relatively low-energy reactive triplet, since its rearrangement is sensitized by Michler s ketone.401 From a Stern-Volmer plot of the effect of naphthalene on the quantum yield for photorearrangement of 35, kjkr was measured to equal 7000.416 Thus if naphthalene quenches triplet 35 at the diffusion-con-... 

In molecules which contain only C-D bonds, the situation is different because the heavier D atom leads to much smaller spacings of vibrational levels, something like 2000 cm-1. The crossing from Ti (v = 0) to S0(v = n) must reach a vibrational level of much higher quantum number so that the overlap of the nuclear wavefunctions is much smaller. The phosphorescence quantum yields and lifetimes are therefore greater in the deuterated compounds. To take one example, the observed phosphorescence lifetime of naphthalene-A8 is 2.3 s, but that of naphthalene-rf8 is 18.4 s, both measured in a rigid glass at 77 K. 

The phosphorescence spectrum of 1,5-naphthyridine is similar to that of naphthalene.86... 

De Silva et al. [28] prepared a naphthalene derivative (3) with logic functions (Scheme 1). Here, the bromonaphthalene unit exhibits phosphorescence in the presence of both the calcium ion and (3-CD [28], However, without them, oxygen quenches the phosphorescence of 2-bromonaphthalene phosphor because the protection effect of (3-CD is absent and photoinduced electron transfer from the tetracarboxylate receptor to the 2-bromonaphthalene phosphor occurs. Thus, phosphorescence output occurs only when the calcium ion and (3-CD inputs are active. The operation of these two inputs with a phosphorescence output corresponds to the AND logic function. The input to the NOT gate is oxygen. In the presence of oxygen without either calcium or (3-CD, the AND gate is disabled. 

Table 19 Phosphorescence lifetimes r (s) for different k spin-sublevels of the 3B U state of benzene and of the 3i 2u state of naphthalene. The benzene values refer to the four mechanisms depicted in Fig. 10 o and i denote the out-of-plane and in-plane polarization, respectively. rav denotes the average lifetime at the high temperature limit. Excitation energies given in eV.

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