Principles of Fluorescence Spectroscopy

276 DYNAMICS OF SOLVENT AND SPECTRAL RELAXATION
P7.3. Lifetime of the R State: Use the data in Figure 7.53 to
calculate the decay time of the 2-PI excimer emission,
assuming this state could be excited directly.
P7.4. Interpretation of Time-Resolved Decays of Acridine:
The excited-state protonation of acridine was examined
by time-resolved measurements of the fluorescence
decays. 139 Neutral acridine is protonated in the excited
state by ammonium ions. The impulse response functions
for acridine in 0.2 M NH 4 NO 3 , pH = 8.3 (Figure
7.49), are listed in Table 7.6.
A. If available, how would you use the absorption
spectra of acridine in 0.05 M NaOH, 0.05 M H 2 SO 4 ,
and 0.2 M NH 4 NO 3 to distinguish between groundstate
and excited-state protonation of acridine?
B. What characteristics of the data in Table 7.6 most
clearly illustrate that an excited-state reaction is
present? Do these data indicate a two-state reaction
or some more complex process? Is the reaction
reversible or irreversible?
P7.5. Interpretation of TRES: Figure 7.58 shows timeresolved
emission spectra of the solvent-sensitive probe
1-anilinonaphthalene (1-AN) in glycerol. 163 The TRES
were obtained using excitation in the center of the
absorption band (337 nm) and excitation on the red edge
of the absorption (416 nm). Explain the difference
between these TRES.
Table 7.6. Time-Resolved Decays of Acridine
in 0.2 M NH 4 NO 3 139
λ (nm) α 1 a τ 1 (ns) α 2 τ 2 (ns)
400 0.503 3.94 –0.001 33.96
410 0.220 4.00 – –
420 0.491 3.88 0.002 25.20
450 0.067 3.90 0.028 30.05
500 –0.010 4.91 0.082 29.13
540 –0.036 3.76 .064 29.83
550 –0.036 3.56 .058 29.94
560 –0.029 3.86 .046 29.90
a The |αi τ i | products are normalized to the steady-state emission intensity at
each wavelength.
Figure 7.58. The time-resolved fluorescence spectra of 1-AN in glycerol
at different excitation wavelengths. Left: 2 ns, 3 ns, and 14 ns
after excitation. Right: 2 and 8 ns after excitation. Revised from [163].