Naphthalene excitation energy

In Section 3.1 it was shown that the photoreduction of benzophenone can be quenched by addition of small amounts of triplet quenchers such as oxygen or ferric dipivaloylmethide.<60) In fact this was presented as evidence that the benzophenone triplet was involved in the photoreduction. This reaction can also be quenched by naphthalene. In the presence of naphthalene, light is still absorbed by benzophenone and thus benzophenone triplets are produced. However, photoreduction products are decreased. On examining this reaction with flash photolysis, triplet-triplet absorptions were observed but these absorptions corresponded to those of the naphthalene triplet. Thus the triplet excitation energy originally present in the benzophenone triplet must have been transferred to naphthalene and since little of the photoreduction product was observed, this transfer must have been fast in relation... 

Fig. 5 Bottom 2PA spectrum for linearly polarized light (intensity in arbitrary units) and (top) polarization ratio of naphthalene in ethanol. 0-0 is the origin of the band (I), the La band (II) is not visible, and the numbers III-VI identify transitions to higher electronic states. The abscissa, representing the total excitation energy, is in units of cm". Reproduced with permission from [46]. 1981, Elsevier...

Fig. 11. Sequence of excitation energies of the naphthalene positive ion, obtained from kinetic energy distribution of the photoelectrons.

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-... 

Flints The assumption that smaller HOMO-LUMO gaps will produce more strongly colored products is true to a first approximation, but not good enough for this problem. In the compounds under study, the HOMO-LUMO gap is largest in naphthalene, which could well explain its lack of color. However, the gap is very similar in anthracene and azulene. To understand their color differences, we need a much more accurate estimate of their excitation energies. 

Table 1. Experimental and Pariser-Parr-Pople results for naphthalene[35] AE is the 0-0 excitation energy, D and E are fine structure constants, p is the spin density,...

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.

Figure 4. Anion excitation energies in eV for naphthalene. (ETS) Energies derived from electron transmission measurements in the gas phase (Soln) optical absorption studies in anions in MTHF glass (PPI, Cl) theoretical energies (PT) values derived from the cation spectrum by applications of the Pairing Theorem...

Quite similar kinetic data are obtained in two photon laser photolysis with, X 3471 A, of naphthalene in toluene. Fluorescence of the naphthalene excited singlet state and absorption spectra of the excited triplet state were observed, no excited species were observed in similar experiments in cyclohexane (21). This suggests that excitation of toluene is two photon into the Sg state followed by rapid internal conversion to the first excited state S-j, which then leads to energy transfer to Naphthalene N. 

The ionization potential and electron affinity of naphthalene were determined experimentally as IP = 8.2 eV and EA 0.0 eV. According to Koopmans theorem it is possible to equate minus the orbital energies of the occupied or unoccupied MOs with molecular ionization potentials and electron affinities, respectively (IP, = - s, and EA = - ). Thus, in the simple one-electron model, the excitation energy of the HOMO->LUMO transition in naphthalene may be written according to Equation (1.22) as... 

As an example of excitation energy transfer studied by time-resolved fluorescence, let us take again the case of the inclusion complex of the multichromophoric cyclodextrin CD-St with oxazine 725 described in Section 7.2.4.2 [15]. Figure 7.9 shows the fluorescence decay of CD-St the very first part of the decay is due to energy transfer [13] from the steroidic naphthalene fluorophores to oxazine 725. Data analysis led to an average decay time for transfer of about 25 ps, which is quite fast, as expected from the short average distance between donor and acceptor ( 9-10 A). 

The triplet state photophysics of naphthalene and a,u-diphenylpolyenes photogenerated in trapped heavy cation exchanged zeolites have been characterized. 0 The application of the modified zeolite environment provides a powerful new method for induction and observation of external heavy atom effects. Triplet excitation energy transport kinetics in vapour deposited naphthalene has been followed by an analysis of the kinetics of phosphorescence and delayed fluorescence. The assorted decays... 

Figure 1. Excitation energy dependence of dispersed fluorescence in naphthalene vapor. (From ref. [6] with permission.)... 

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