Molecular and Supramolecular Photochemistry
Instructor: V. Ramamurthy (murthy)
University of Miami, Coral Gables, FL
Email: murthy1@miami.edu; VR@Ramamurthy.net
Class timing: Thursday, 9-11 AM
Oct 3 to Dec 12
Suggested Textbooks
The first seven chapters of PMP and MMPOM are identical, and this course will cover Ch 1-7
The Approach: “The concepts of photochemistry are described quantitatively and most effectively by the
mathematics of quantum mechanics. However, this course (and the text) is directed at students who do not
possess the mathematical background necessary for understanding through quantum mechanics. Instead,
we will focus on classical representations that are readily visualizable and capture the essence of most of the
critical features of quantum mechanics that are needed to understand organic photochemistry.”
About this Course
Deals with interaction of Light with Materials, Molecules and in
turn Electrons
What is light?
What is a material?
What is a molecule?
What is an electron?
How do light and an electron interact in a molecule?
What are the consequences of such an interaction?
How to control the interaction?
How does Nature utilizes light?
What are the uses of light in our everyday life?
Syllabus
Introduction (Ch. 1)
Why photochemistry?
What is photochemistry?
Molecules: Electronic, Vibrational and Spin States (Ch 2)
Generation of Molecules in electronically excited states (Ch 3 & 4)
Selection rules for spin allowed and spin forbidden transitions, absorption and emission
Deactivation of Molecules: Radiative Transitions, Fluorescence, Phosphorescence, Excimer/exciplex, Delayed fluorescence,
TICT emission, Applications of emission
Deactivation of Molecules: Radiationless Transitions (Ch 5)
Mechanism of spin inter-conversion, Spin-orbit coupling, Heavy atom effect; Properties of triplets
Deactivation of Molecules: Energy and Electron Transfer (Ch 7)
Singlet-Singlet ET, Triplet-Triplet ET, Triplet-Triplet annihilation and Singlet fission
Mechanism of electron transfer, Contributions of Weller and Marcus, Long range electron transfer
Role of energy and electron transfer in natural and artificial photosynthesis
Reaction Dynamics (Ch 6)
Grade: Based on a final written examination to be given during the exam period.
Please note 1: I have already scheduled trips to conferences during the semester. Possibly I may miss one or two
weeks.
Konark Suryanar koil Modhera
Ranakpur
Recognizing the importance of light, SUNits
ultimate source has been worshipped in
many ancient cultures.
Only a few have gone beyond to probe its
nature.
Oil lamp
Humphry Davy
Fluorescent lamp
Edmund Germer1930s
Filament lamp
Thomas Edison
Light emitting diodes (1960s)
Light: Prosperity through basic science
Candle lamp
200 BC India
Light is both a Wave and a Particle !
-Light behaves like a wave
when it propagates through
space
-And as a particle when it
interacts with matter
Light is an EM wave
n =
l
c
Characterized by:
Ø Wavelength (λ)
Ø Amplitude (A)
Ø Frequency (ν)
– The amplitude is the wave’s height from the origin
to a crest.
The Wave Nature of Light
Uses of electromagnetic radiations of different wavelengths
l = c/n n = c/l
Light = Photon
“Light is something like
raindrops-each little lump of
light is called a photon-and if
the light is all one color, all the
"raindrops" are the same size.”
Richard P. Feynman
Nobel Prize, 1965
Light is made up of photons. Light is
measured in terms of Einstein. One
Einstein is the energy in one mole
(6.022 x 1023) of photons. Energy of
one E depends on the frequency of
photon.
Liquid water is made up of
molecules. Amount is measured in
terms of mole (M). One mole
contains 6.022×1023 molecules
(Avogadro's number). Weight of one
M depends on the weight of the
molecule.
• g-ray Medicinal applications (cancer therapy)
• X-ray Medicinal applications
• Ultraviolet Lithographic, medical/dental, hygienic/killing
bacteria
• Visible light Fiber optic communications, TV & computer
screens, medical, lithographic, photography
• Infrared Heating devices, night vision goggles, remote
controls
• Microwave Cooking, Cell phones, remote sensing, army
• Radiowave Radios, TV, mobile phones, computer networks
Light in our life
1917: Albert Einstein derives the
theoretical basis for the laser.
1960: The first working (ruby) laser.
LASER Invention and Innovation
(Light Amplification by the Stimulated Emission of Radiation)
Charles H. Townes Aleksandr M. Prokhorov
Nicolay G. Basov
The Nobel Prize in Physics 1964
"for fundamental work in the field of
quantum electronics, which has led to
the construction of oscillators and
amplifiers based on the maser-laser
principle."
1965: The compact laser disc (CD) invented.
1974: A laser-driven barcode scanner
used for the first time.
Laser Applications
The world market for laser technology is now over
$ 16.7 billion a year (2022)
• Medical
• Metallurgical
• Electronic and computer
• Military
• Communications
• Microscopy
• Metrological
• Entertainment industry
 Photomedicine
 Lithography
 TiO2: Environmental Cleanup
 Solar Energy Conversion
 Industrial Synthesis of Chemicals
 Photography, Xeorography and Holography
 Sunscreen, Photochromic Glass
 Photostabilization
 Photocuring
Niels Ryberg Finsen
Finsen Medical Light Institute, Copenhagen, Denmark
The Nobel Prize in Physiology or Medicine, 1903
Prize motivation: "in recognition of his contribution to the treatment
of diseases, especially lupus vulgaris, with concentrated light
radiation, whereby he has opened a new avenue for medical science."
For a time, light therapy was widespread, but eventually
it was supplanted by antibiotics.
v Phototherapy - Jaundice treatment
v PUVA therapy - Skin disorders, Blood cancer
v Photodynamic therapy - Cancer
v Lasik surgery - Vision correction
Photomedicine
Jaundice
Phototherapy for Neonatal Jaundice Treatment
v Accumulation of the potentially toxic
yellow liphophilic bilirubin in human
serum leads to Jaundice.
v If the percentage of bilirubin
increases to 15-25 mg/100 ml, it will
lead to hyperbilirubinemia.
v Severe hyperbilirubinemia cases,
sufficient pigment may partition into
the brain to cause irreversible
damage, even death.
McDonagh etal., Science, 208, 1980, 145-151.
NH N
NH HN
H-O-C C-O-H
O
O
OO
H H
Bilirubin
Why bilirubin is lipophilic (hydrophobic) ?
Natural Cure for Jaundice
Different ways to cure jaundice
 Wait till liver matures soon enough to clear bilirubin unaided.
 Exchange transfusion: blood along with threatening pigment
drained and replaced with clean blood.
 Phototherapy - irradiate the baby with light.
Discovery of phototherapy
The discovery of phototherapy stems from the observations of Sister J.
Ward, a nurse in U.K.
Evening walk with hyperbilirubinemia patients - lead to discovery of
phototherapy by scientists.
“light converts bilirubin to a less hydrogen bonded
(more water soluble) isomer”
Phototherapy - Jaundice Treatment
Psoriasis
Vitiligo Acute dermatitis
Polymorphic light eruption
Skin Disorders
 Egyptians and Asian Indians practiced this therapy centuries ago.
 Boiled extracts of fruits of plants Ammi majus in Egypt and Psoralea
Corylifolia L in India plus sunlight cured vitiligo.
 In 1988, PUVA was the first FDA (Food and Drug Administration)
approved selective immunotherapy for skin disorders including
cancer.
PUVA- therapy
Psoralen + UVA = PUVA therapy
OO
O
OCH3
What is UV-A light?
 Methoxsalen capsules are taken two hours before
exposure to UVA.
 Bath PUVA: hands and/or feet are soaked in a dilute
solution of methoxsalen for 30 minutes, then exposed
to UVA.
 A few patients may be treated with topical tripsor
PUVA - a lotion is applied on the affected areas 10
minutes before UVA exposure.
How PUVA therapy is done ?
PUVA therapy
OO
O
OCH3
Psoralen + Ultraviolet A = PUVA
Photoadduct representation with DNA
• Intercalation
• Monofunctional adduct (
3, 4 with pyrimidine base)
• Bifunctional crosslinked
adduct(3, 4 and 4’, 5’
with pyrimidine bases)
Photodynamic therapy
 Photodynamic therapy first used in 1978.
 Currently several photodynamic drugs are available on the market.
 Approved for the treatment of esophageal and lung cancers.
Chlorins PhthalocyaninesPorphyrins
How does photodynamic therapy work?
 PDT requires sensitizer, light and oxygen
in the target tissue.
 Light generates reactive oxygen species.
 Reactive oxygen species can kill targeted
cells either by necrotic mechanisms or by
initiating the apoptotic cascade.
Ideal wavelength 650nm
Photodynamic therapy
Light activated PS drug
generates singlet oxygen from
molecular oxygen and kills
cancer cells
Laser light source
Directed at target tissue
PDT effect kills cells
R. Srinivasan S. Blum J. Wyne
1981: Discovery of laser ablation technique.
1995: US FDA approval of human Lasik surgery.
2002: Inducted into US Inventors Hall of Fame.
Lithography to Lasik Surgery
For the pioneering discovery of excimer laser
ablative photodecomposition of human and
animal tissue, laying the foundation for PRK
and LASIK, laser refractive surgical
techniques that have revolutionized vision
enhancement.
National Medal of Technology and Innovation (2011)
Lithography to Lasik Surgery
R. Srinivasan and W. Leigh, J. Am. Chem. Soc., 104, 6784, 1982.
193 nm 532 nm
B. Garrison and R. Srinivasan, J. Appl. Physics, 57, 2909, 1985
Photoablation with Excimer Lasers
1987: Lasik surgery
Defined areas of a cornea can be removed by ablating the tissue to a predetermined length.
Far-UV laser irradiation produces a trench with sharp and cleanly defined boundaries by light
microscopy. There are no changes in the adjacent tissues due to thermal effects.
Significantly, laser ablation can be used to remove a shaped area of cornea to any depth.
S. Trokel, R. Srinivasan and B. Braren, American. J. Opthomology, 96, 710, (1983)
S. Trokel, Refractive and Cosmetic Surgery, 6, 357, 1990
R. Srinivasan, Science 234, 565, 1986
Photochemistry in Real Life Systems
Ø PYP and plant growth (cis-trans)
Ø Phytochrome - circadian clock (cis-trans)
Ø Phototropism (e-transfer)
(bending and growth of plants)
Ø Vision (cis-trans)
Ø Photosynthesis (e-transfer)
Role of Photoactive Yellow Protein (PYP) in plant growth
In dark In light
Phytochrome
Ragnar Granit Haldan Keffer Hartline George Wald
"for their discoveries concerning the primary physiological and
chemical visual processes in the eye"
The Nobel Prize in Physiology or Medicine 1967
Plants that commonly grow in the shade benefit from having a variety of lightabsorbing
pigments. Each pigment can absorb different wavelengths of light, which
allows the plant to absorb any light that passes through the taller trees.
Survival Strategy: Photosynthesis
Joseph Priestley
1733–1804
Joseph Priestley published in 1774: “Green plants absorb
carbon dioxide from the atmosphere and give of oxygen”.
Light Energy Harvested by Plants
6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2
Ingenhousz, along with Benjamin Franklin and a few other traveling
companions paid a visit to scientist Joseph Priestly, who had recently
discovered that plant leaves absorb and emit gases. That exchange led
Ingenhousz to eventually discover the chemistry that forms the foundation of
nearly every food chain on Earth is light: photosynthesis.
1730 – 1799
Photosynthesis and Solar Energy
M. Calvin
1911-1997
The Nobel Prize in Chemistry 1961
R. Marcus
The Nobel Prize in Chemistry 1992
J. Deisenhofer R. Huber H. Michel
The Nobel Prize in Chemistry 1988
Joseph Priestley
1733–1804
“On the arid lands there will spring up industrial colonies without smoke and
without smokestacks, forests of glass tubes will extend over the plains, and glass
buildings will rise everywhere; inside of these will take place the photochemical
processes that hitherto have been the guarded secret of the plants, but have been
mastered by human industry which will know how to make them bear even more
abundant fruit than nature, for nature is not in a hurry and mankind is.”
(G. Ciamician, Science 1912, 36, 385.)
Giacomo Ciamician
1857-1922