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Test required to obtain credit and grade in the course
C9911 Molecular and Supramolecular Photochemistry (Autumn 2024)
Answer all questions and submit the answer sheets to Prof. Petr Klan by
January 15, 2025.
Note: All answers are available in the lecture notes (pdf) posted on MUNI course website. If
you need more information, please read N. J. Turro, J. C. Scaiano, and V. Ramamurthy, Modern
Molecular Photochemistry of Organic Molecules. University Science Books, 2010; (Ch 1-7) or
P. Klán and J. Wirz, Photochemistry of Organic Compounds: From Concepts to Practice, WileyBlackwell,
2009
NAME:
(1) In the table below fluorescence quantum yields of several azulenes are listed.
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(a) Why azulene’s fluorescence quantum yield depends on the substituent?
(b) Generally, in most molecules, from where does the fluorescence originate, S1, S2 or S3?
(2) The tabulated data below give considerable insight into the factors that control the
radiationless process. Consulting the table answer the listed questions:
(a) Why does the quantum yield of fluorescence decrease with the substituent---F, Cl, Br and I?
(b) Why does the quantum yield of phosphorescene increase with the substituent---F, Cl, Br and I?
(c) Although the quantum yield of fluorescence decreases with the substituent, why the rate
constant of fluorescence does not change with the substituent---F, Cl, Br and I?
(3) (a) Why excited singlet (S1) is higher in energy than the corresponding excited triplet (T1) of
the same electronic configuration?
(b) Between naphthalene and tetracene which one would have a smaller singlet–triplet gap?
(c) Bteween benzophenone and stilbene which one will larger singlet–triplet gap?
(4) In one of pioneering studies, Zewail mapped the photodissociation surface of ICN. Needed
information to answer the questions are included in the figures below.
(a) How did Zewail monitor the photodissociation?
(b) What information did he get by exciting the excited species with different wavelengths,
391.4, 390.4, 389.8 and 388.9 nm?
(c) Why did he not observe the oscillation that he noted during the photodissociation of NaI
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Rise and decay of laser induced fluorescence signal of CN*
388.9 nm
389.8 nm
390.4 nm
391.4 nm
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(5) The orbital correlation diagram for disrotatory ring opening of cyclobutene to butadiene is
shown below.
(a) Using this construct a state correlation diagram.
(b) Using the state diagram and applying the concept of avoided crossings, build an energy
surface that helps to track the reaction.
(c) In the above figure sketch the pathway an excited cyclobutene would take to reach butadiene.
(6) The emission spectrum of pyrene with two distinct bands is shown below.
(i) Explain with the help of a potential energy diagram (ground & excited state) why the
emission at longer wavelength is structureless?
(ii) There is a delay in the appearance of the longer wavelength emission compared to the
shorter wavelength emission. Why?
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