10594 J. Phys. Chem. B, Vol. 108, No. 29, 2004
Bader et al.
TABLE 3: Wavelengths of the Main Sites in the Shpol’skii Excitation and Emission Spectraa
λexc
∆EH - ∆ED
ZPEH,N - ZPEH,N*
λem
∆EH - ∆ED
ZPEH,T - ZPEH,T*
(cm-1
(nm)
(cm-1
60
)
(cm-1
205
)
(nm)
(cm-1
)
)
3HF
3DF
3HF-4′OMe
3DF-4′OMe
3HC-F
3DC-F
365.75
364.95
376.45
375.82
375.60
375.12
513.14
514.09
518.95
519.67
523.55
523.90
-36
-123
-91
-44
44
34
150
116
-27
-13
a For every compound, the difference between λH and λD is used to calculate the difference in ZPE, both for the normal form and the tautomeric
form.
the T state compared to the T* state implies that the acidity of
this group becomes higher in the ground state. Consequently,
the weakening of the O-H bond will increase the C-O bond
order at the 4 position. This explains the high rate of BPT in
3HF. Electron donating substituents in 3HF-4′OMe and 3HC-
F, however, will reduce both effects and therefore cause a
reduced BPT rate.
It can be concluded that the electron donating substituents
have a strong influence on the proton tunneling rates of 3HF
and its derivatives. They can significantly reduce the rate of
both ESIPT and BPT. These results will help us understand the
photophysical behavior of this important class of compounds.
Acknowledgment. A.P.D. acknowledges the “ULTRA”
program of the European Science Foundation for the travel grant
to Amsterdam. A. V. Turov is acknowledged for providing the
NMR spectra.
Figure 4. ZPE levels of the protonated compound (subscript index
“H”) and deuterated compound (subscript index “D”) in ground-state
N and excited-state N*. Energy differences ∆EH and ∆ED are the
measured values obtained from the (0,0) bands in the Shpol’skii
excitation spectrum. Combining the equation for ∆EH and ∆ED results
in eq 2.
References and Notes
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