Photochemistry is the branch of chemistry concerned with chemical reactions caused by light absorption. Photochemical reactions proceed differently than thermal reactions and can form thermodynamically disfavored products or overcome large activation barriers. When a molecule absorbs light, it is elevated to an excited state. The Grotthuss–Draper law states that light must be absorbed for a photochemical reaction to occur. Absorbed light can excite a molecule to different singlet or triplet states, which can then relax through radiationless or radiative processes like fluorescence or phosphorescence. Experimental factors like light sources, reactors, solvents, and wavelength selection influence photochemical reactions.
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The all the content in this profile is completed by the teachers, students as well as other health care peoples.
thank you, all the respected peoples, for giving the information to complete this presentation.
this information is free to use by anyone.
For UG students of All Engineering Branches (Mechanical Engg., Chemical Engg., Instrumentation Engg., Food Technology) and PG students of Chemistry, Physics, Biochemistry, Pharmacy
The link of the video lecture at YouTube is
https://www.youtube.com/watch?v=t3QDG8ZIX-8
This presentation is about Classical theory of Raman Effect. This lecture gives brief explanation about rayleigh scattering and raman scattering and about the classical theory which talks about the polarisation of molecule and how the polarisation relates with raman scattering. Have fun Learning!
Mossbauer spectroscopy - definition, principle , parameters, isomer shift , quadrupole splitting , magnetic splitting (hyperfine splitting), working diagram. it is based on nuclear resonance gamma radiation
Photochemistry
ELECTROMAGNETIC SPECTRUM
LAW GOVERNING ABSORPTION OF LIGHT
LAW OF PHOTOCHEMISTRY
Grotthurs-Drapper law.
Einstein Stark law of photochemical equivalence
ELECTRONIC TRANSITIONS
Jablonski Diagram
QUANTUM YIELD
Use Of Photochemistry
Chemistry of vision
Photosynthesis in plant
Formation of Vitamin D
Fluorescent dyes in traffic
Photodynamic therapy
For UG students of All Engineering Branches (Mechanical Engg., Chemical Engg., Instrumentation Engg., Food Technology) and PG students of Chemistry, Physics, Biochemistry, Pharmacy
The link of the video lecture at YouTube is
https://www.youtube.com/watch?v=t3QDG8ZIX-8
This presentation is about Classical theory of Raman Effect. This lecture gives brief explanation about rayleigh scattering and raman scattering and about the classical theory which talks about the polarisation of molecule and how the polarisation relates with raman scattering. Have fun Learning!
Mossbauer spectroscopy - definition, principle , parameters, isomer shift , quadrupole splitting , magnetic splitting (hyperfine splitting), working diagram. it is based on nuclear resonance gamma radiation
Photochemistry
ELECTROMAGNETIC SPECTRUM
LAW GOVERNING ABSORPTION OF LIGHT
LAW OF PHOTOCHEMISTRY
Grotthurs-Drapper law.
Einstein Stark law of photochemical equivalence
ELECTRONIC TRANSITIONS
Jablonski Diagram
QUANTUM YIELD
Use Of Photochemistry
Chemistry of vision
Photosynthesis in plant
Formation of Vitamin D
Fluorescent dyes in traffic
Photodynamic therapy
431chem course Aljouf university, college of science, chemistry department.
. Fates of Excited State Molecules.
• Absorption and emission of electromagnetic radiation.
• Einstein coefficients, absorption probabilities.
• Fluorescence and phosphorescence.
• Internal conversion and intersystem crossing.
• Photodissociation and predissociation.
• Jablonski diagram.
. Lasers.
• Requirements for laser action.
• Population inversions.
• Properties of laser radiation.
• Examples of lasers.
• Applications in spectroscopy and photochemistry.
Dr Wael A. Elhelece.
PHOTOCHEMISTRY BASIC PRINCIPLE AND JABLONSKI DIAGRAMsuriyachem27
Photochemistry is the branch of chemistry in which study of chemical reactions take place by
the absorption of electromagnetic radiation or by molecules absorb light radiation
(electromagnetic radiation) particularly the visible (wavelength from (400-750) and ultra violet region (wavelength from 100-400nm ), the molecules generally get activated due to
electronic excitation. When electromagnetic radiation is absorb in the ultraviolet/visible
region the molecules get excited to higher electronic state. This involves the promotion of an
electron from bonding molecular orbital to antibonding molecular orbital. According to the quantum theory, both matter and light are quantised, and only certain
specific energies of light are absorbed by specific organic molecule for its excitation. The
absorption or emission of light occurs by the transfer of energy as photons. All photochemical and photo physical processes are initiated by the absorption of a photon of visible or ultraviolet radiation leading to the formation of an electronically - excited state. The molar absorptivity (formerly called the extinction coefficient) of a compound constant
that is characteristic of the compound at a particular wavelength. The Jablonski diagram is a pictorial illustrated of different energy states which are absorbed by molecules. This
partial energy diagram represents the energy of a photo luminescent molecule in its different energy states.The life time of singlet excited state S1 is long hence in this state has done many physical and chemical processes. Molecules returns to its ground state, S0 from excited singlet S1,/ S2 state by release energy as heat, but this is generally quite slow because the amount of energy is large between S0 and S1. This process is called internal conversion. When molecules return to its ground state S0 from excited state S1,/ S2 by giving off
energy in the light form within 10-9 seconds. This process is known as Fluorescence.
This pathway is not very common because it is relatively slow. For smaller, diatomic
and rigid molecules (mainly aromatic compounds) show fluorescence. This is because
emitted fluorescent light is of lower energy than absorbance light. Most molecules in the S1 state may drop to triplet state (T1) (S1→T1). This is
energetically slow process. However, if the singlet state S1 is long lived, the S1 →
T1 conversion occurs by a process called intersystem crossing. It is important
phenomenon in photochemistry. For every excited singlet state there exist
corresponding triplet states. Since transition from ground state singlet (S0) to triplet
state (T1) is forbidden, intersystem crossing is the main source of excited triplet
state. This is one way of populating the triplet state. The efficiency in intersystem
crossing depends on the S1 → T1 energy gap.
The Role of Ultrafast Processes in Human VisionHassen Iqbal
Human vision occurs through a process known as phototransduction, which is the conversion of light energy into electrical and chemical signals. The first step in phototransduction is an ultrafast process that occurs in femtoseconds. In this minireview we will discuss what happens when a photon of light enters the photoreceptors in the eye. We will focus mainly on the rhodopsin pigment (also known as visual purple) contained in the rod photoreceptor found in rod cells that are responsible for black and white vision.
Authors: Hassen Iqbal, Vas Stavros
Spectroscopy for Pharmaceutical Analysis and Instrumental Method of Analysis....Yunesalsayadi
Spectroscopy for Pharmaceutical Analysis and Instrumental Method of Analysis.
Atomic spectroscopy, Molecular Spectroscopy, Beer Lambert's Law, Fundamental Laws of Photometry, application of beer lambert law in equilibrium constant, Chromophore, Auxochrome, Bathochromic shift, Hypsochromic shift, Hypochromic and Hyperchromic effects, Effect of solvent on absorption spectra
Biological screening of herbal drugs: Introduction and Need for
Phyto-Pharmacological Screening, New Strategies for evaluating
Natural Products, In vitro evaluation techniques for Antioxidants, Antimicrobial and Anticancer drugs. In vivo evaluation techniques
for Anti-inflammatory, Antiulcer, Anticancer, Wound healing, Antidiabetic, Hepatoprotective, Cardio protective, Diuretics and
Antifertility, Toxicity studies as per OECD guidelines
The French Revolution, which began in 1789, was a period of radical social and political upheaval in France. It marked the decline of absolute monarchies, the rise of secular and democratic republics, and the eventual rise of Napoleon Bonaparte. This revolutionary period is crucial in understanding the transition from feudalism to modernity in Europe.
For more information, visit-www.vavaclasses.com
Francesca Gottschalk - How can education support child empowerment.pptxEduSkills OECD
Francesca Gottschalk from the OECD’s Centre for Educational Research and Innovation presents at the Ask an Expert Webinar: How can education support child empowerment?
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Dive into the world of AI! Experts Jon Hill and Tareq Monaur will guide you through AI's role in enhancing nonprofit websites and basic marketing strategies, making it easy to understand and apply.
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An EFL lesson about the current events in Palestine. It is intended to be for intermediate students who wish to increase their listening skills through a short lesson in power point.
Model Attribute Check Company Auto PropertyCeline George
In Odoo, the multi-company feature allows you to manage multiple companies within a single Odoo database instance. Each company can have its own configurations while still sharing common resources such as products, customers, and suppliers.
Acetabularia Information For Class 9 .docxvaibhavrinwa19
Acetabularia acetabulum is a single-celled green alga that in its vegetative state is morphologically differentiated into a basal rhizoid and an axially elongated stalk, which bears whorls of branching hairs. The single diploid nucleus resides in the rhizoid.
1. PHOTOCHEMISTRY
Photochemistry is the branch of chemistry concerned with the chemical effects of light.
Generally, this term is used to describe a chemical reaction caused by absorption
of ultraviolet (wavelength from 100 to 400 nm), visible light (400 - 750 nm) or infrared radiation
(750 - 2500 nm).[1]
Photochemical reactions are valuable in organic and inorganic chemistry because they
proceed differently than thermal reactions. Many thermal reactions have their photochemical
counterpart. Photochemical paths offer the advantage over thermal methods of forming
thermodynamically disfavored products, overcoming large activation barriers in a short period of
time, and allowing reactivity otherwise inaccessible by thermal processes.
Everyday examples include photosynthesis, degradation of plastics or formation
of vitamin D with sunlight.
Photochemical immersion well reactor (50 mL) with a mercury-vapor lamp
Grotthuss–Draper law or first law of photochemistry
Photoexcitation is the first step in a photochemical process where the reactant is
elevated to a state of higher energy, an excited state. The first law of photochemistry, known as
the Grotthuss–Draper law (for chemists Theodor Grotthuss and John W. Draper), states that light
must be absorbed by a chemical substance in order for a photochemical reaction to take place.
For each photon of light absorbed by a chemical system, no more than one molecule is activated
for a photochemical reaction, as defined by the quantum yield.[2]
2. When a molecule in ground state (S0) absorbs light, one electron is excited to a higher
orbital level. This electron maintains its spin according to spin selection rule; as other transitions
violate the law of conservation of angular momentum. This excitation to a higher singlet state can
be from HOMO to LUMO or to a higher orbital, thus being possible different singlet excitation
states S1, S2, S3… depending on its energy.
Kasha's rule stipulates that higher singlet states would quickly relax by radiationless
decay or internal conversion, IC, to S1. Thus, S1 is usually, but not always, the only relevant
singlet excited state. This excited state S1 can further relax to S0 by IC, but also by an allowed
radiative transition from S1 to S0 that emits a photon; this process is called fluorescence.
Jablonski diagram.Radiative paths are represented by straight arrows and non- radiative paths by curly lines.
Alternatively, it is possible for the excited state S1 to undergo spin inversion and to
generate a different excited state with the two unpaired electrons with the same spin, thus having
a triplet multiplicity, T1. This violation of the spin selection rule is possible by intersystem
crossing, ISC, of vibration and electronic levels of S1 and T1. According to Hund's rule of
maximum multiplicity, this T1 state would be somewhat more stable than S1.
This triplet state can relax to ground state S0 by radiation less IC or by a radiation pathway that
is called phosphorescence. This process implies a change of electronic spin, which is forbidden
by spin selection rules, making phosphorescence (from T1 to S0) much slower than fluorescence
(from S1 to S0). Thus, triplet states generally have longer lifetimes than singlet states. These
transitions are usually summarized in a state energy diagram or Jablonski diagram, the paradigm
of molecular photochemistry.
These excited species, either in S1 or T1, have a half empty low energy orbital,
consequently are more oxidizing. But at the same time, they have an electron in a high energy
orbital, thus they are more reducing. In general, excited species are prone to participate in
electron transfer processes.
3. Experimental set-up
Photochemical immersion well reactor (750 mL) with a mercury-vapor lamp
Photochemical reactions require a light source that emits wavelengths corresponding to
an electronic transition in the reactant. In the early experiments (and in everyday life), sunlight
was the light source, although it is polychromatic. Mercury-vapor lamps are more common in the
laboratory. Low pressure mercury vapor lamps mainly emit at 254 nm. For polychromatic
sources, wavelength ranges can be selected using filters. Alternatively, LEDs and Rayonet lamps
emit monochromatically.
Schlenk tube containing slurryof orange crystals of Fe2(CO)9 in acetic acid after its photochemical synthesis from Fe(CO)5.
The mercury lamp (connected to white power cords) can be seen on the left, set inside a water-jacketed quartz tube.
The emitted light must of course reach the targeted functional group without being
blocked by the reactor, medium, or other functional groups present. For many
applications, quartz is used for the reactors as well as to contain the lamp. Pyrex absorbs at
wavelengths shorter than 275 nm. The solvent is an important experimental parameter. Solvents
are potential reactants and for this reason, chlorinated solvents are avoided because the C-Cl
4. bond can lead to chlorination of the substrate. Strongly absorbing solvents prevent photons from
reaching the substrate. Hydrocarbon solvents absorb only at short wavelengths and are thus
preferred for photochemical experiments requiring high energy photons. Solvents containing
unsaturation absorb at longer wavelengths and can usefully filter out short wavelengths. For
example, cyclohexane and acetone "cut off" (absorb strongly) at wavelengths shorter than 215
and 330 nm, respectively.
Principles
In the case of photochemical reactions, light provides the activation energy.
Simplistically, light is one mechanism for providing the activation energy required for many
reactions. If laser light is employed, it is possible to selectively excite a molecule so as to
produce a desired electronic and vibrational state. Equally, the emission from a particular state
may be selectively monitored, providing a measure of the population of that state. If the chemical
system is at low pressure, this enables scientists to observe the energy distribution of the
products of a chemical reaction before the differences in energy have been smeared out and
averaged by repeated collisions.
The absorption of a photon of light by a reactant molecule may also permit a reaction to
occur not just by bringing the molecule to the necessary activation energy, but also by changing
the symmetry of the molecule's electronic configuration, enabling an otherwise inaccessible
reaction path, as described by the Woodward–Hoffmann selection rules. A 2+2 cycloaddition
reaction is one example of a pericyclic reaction that can be analyzed using these rules or by the
related frontier molecular orbital theory.
Some photochemical reactions are several orders of magnitude faster than thermal
reactions; reactions as fast as 10−9
seconds and associated processes as fast as 10−15
seconds
are often observed.
The photon can be absorbed directly by the reactant or by a photosensitizer, which
absorbs the photon and transfers the energy to the reactant. The opposite process is
called quenching when a photo exited state is deactivated by a chemical reagent.
Most photochemical transformations occur through a series of simple steps known as
primary photochemical processes. One common example of these processes is the excited state
proton transfer.