Question 3 Some photophysical parameters (lifetime, t, and quantum yield, $) for fluorescence (n = 370 nm) and phosphorence (p = 580 nm) of pyrene, 1-chloropyrene and 1-bromopyrene are given in the table below, as measured at room temperature (RT) and at 77 K in a frozen ethanol glass. фе τη Фл Фр Tp (RT) (RT) (77 K) (77 K) (77 K) (ns) (s) X = H 0.72 530 0.9 < 0.001 0.39 X X = CI 0.22 75 0.59 0.058 0.10 X = Br 0.032 2 0.17 0.085 0.004 fl = fluorescence; p = phosphorescence (a) Construct a Jablonski diagram for pyrene (X = H) at 77K. (b) Pyrene (X = H) has an absorbance maximum, Amax, at 330 nm and a fluorescence maximum, 11, at 370 nm. Why does this difference in wavelengths occur? (c) Explain why the lifetime for phosphorescence is longer than that for fluorescence. (d) Why does the fluorescence quantum yield increase with decreasing temperature? (e) Explain the trend in phosphorescence quantum yield as X is varied.
Question 3 Some photophysical parameters (lifetime, t, and quantum yield, $) for fluorescence (n = 370 nm) and phosphorence (p = 580 nm) of pyrene, 1-chloropyrene and 1-bromopyrene are given in the table below, as measured at room temperature (RT) and at 77 K in a frozen ethanol glass. фе τη Фл Фр Tp (RT) (RT) (77 K) (77 K) (77 K) (ns) (s) X = H 0.72 530 0.9 < 0.001 0.39 X X = CI 0.22 75 0.59 0.058 0.10 X = Br 0.032 2 0.17 0.085 0.004 fl = fluorescence; p = phosphorescence (a) Construct a Jablonski diagram for pyrene (X = H) at 77K. (b) Pyrene (X = H) has an absorbance maximum, Amax, at 330 nm and a fluorescence maximum, 11, at 370 nm. Why does this difference in wavelengths occur? (c) Explain why the lifetime for phosphorescence is longer than that for fluorescence. (d) Why does the fluorescence quantum yield increase with decreasing temperature? (e) Explain the trend in phosphorescence quantum yield as X is varied.
Principles of Instrumental Analysis
7th Edition
ISBN:9781305577213
Author:Douglas A. Skoog, F. James Holler, Stanley R. Crouch
Publisher:Douglas A. Skoog, F. James Holler, Stanley R. Crouch
Chapter15: Molecular Luminescence Spectrometry
Section: Chapter Questions
Problem 15.6QAP
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Topic: Photochemistry and Photophysics of Supramolecules
Transcribed Image Text:Question 3
Some photophysical parameters (lifetime, t, and quantum yield, $) for fluorescence (n = 370 nm)
and phosphorence (p = 580 nm) of pyrene, 1-chloropyrene and 1-bromopyrene are given in the
table below, as measured at room temperature (RT) and at 77 K in a frozen ethanol glass.
фе
τη
Фл
Фр
Tp
(RT)
(RT)
(77 K)
(77 K)
(77 K)
(ns)
(s)
X = H
0.72
530
0.9
< 0.001
0.39
X
X = CI
0.22
75
0.59
0.058
0.10
X = Br 0.032 2
0.17
0.085
0.004
fl = fluorescence; p = phosphorescence
(a) Construct a Jablonski diagram for pyrene (X = H) at 77K.
(b) Pyrene (X = H) has an absorbance maximum, Amax, at 330 nm and a fluorescence
maximum, 11, at 370 nm. Why does this difference in wavelengths occur?
(c) Explain why the lifetime for phosphorescence is longer than that for fluorescence.
(d) Why does the fluorescence quantum yield increase with decreasing temperature?
(e) Explain the trend in phosphorescence quantum yield as X is varied.
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