PHOTOCHEMICAL TRANSFORMATIONS

1. PHOTOCHEMICAL
TRANSFORMATIONS

2. PHOTOBIOLOGY
• "Photobiology is broadly defined to include all
biological phenomena involving non-ionizing
radiation. It is recognized that photobiological
responses are the result of chemical and/or
physical changes induced in biological systems
by non-ionizing radiation."

3. • Non-ionizing radiation produces excited states
in molecules due to the absorption of one or
more photons. Excited-state molecules can
react with adjacent molecules, but most
frequently they undergo photochemical and
photophysical changes within their own
molecular structure.

4. • Non-ionizing radiation is grouped into three
main regions; Ultraviolet (UV) radiation (short
wavelengths that are not visible to man),
Visible radiation (longer wavelengths than UV
radiation), and Infrared radiation (still longer
wavelengths, and also not visible to man).

6. • The UV region is generally divided into three
regions (especially in Photomedicine), i.e., the
UV-C region, which is generally defined as being
in the wavelength region from 100-280
nanometers (nm), the UV-B region as 280-320
nm, and the UV-A region as 320-400 nm. Other
terms commonly used for the UV region are Far-
UV (210-300 nm) and Near-UV (300-380 nm).
The Visible region is generally defined as 400-760
nm, and the Infrared region lies above 760 nm

7. Photochemical reaction
• Photochemical reaction, a chemical
reaction initiated by the absorption
of energy in the form of light. The
consequence of molecules’ absorbing light is
the creation of transient excited states whose
chemical and physical properties differ greatly
from the original molecules.

8. • These new chemical species can fall apart,
change to new structures, combine with each
other or other molecules, or
transfer electrons, hydrogen atoms, protons,
or their electronic excitation energy to other
molecules. Excited states are
stronger acids and stronger reductants than
the original ground states.

9. • It is this last property that is crucial in the most
important of all photochemical
processes, photosynthesis, upon which almost
all life on Earth depends. Through
photosynthesis, plants convert the energy of
sunlight into stored chemical energyby
forming carbohydrates from atmospheric carbon
dioxide and water and releasing
molecular oxygen as a byproduct. Both
carbohydrates and oxygen are needed to sustain
animal life. Many other processes in nature are
photochemical.

10. Ultraviolet RADIATION
• Ultraviolet (UV) is an electromagnetic radiation with
a wavelength from 10 nm to 400 nm, shorter than that of visible
lightbut longer than X-rays. UV radiation constitutes about 10% of
the total light output of the Sun, and is thus present in sunlight. It is
also produced by electric arcs and specialized lights, such
as mercury-vapor lamps, tanning lamps, and black lights. Although
it's not considered an ionizing radiation because its photons lack
the energy to ionize atoms, long-wavelength ultraviolet radiation
can cause chemical reactions and causes many substances to glow
or fluoresce. Consequently, the chemical and biological effects of
UV are greater than simple heating effects, and many practical
applications of UV radiation derive from its interactions with
organic molecules.

11. • It is also produced by electric arcs and
specialized lights, such as mercury-vapor
lamps, tanning lamps, and black lights.
Although it's not considered an ionizing
radiation because its photons lack the energy
to ionize atoms, long-wavelength ultraviolet
radiation can cause chemical reactions and
causes many substances to glow or fluoresce.

12. • Consequently, the chemical and biological
effects of UV are greater than simple heating
effects, and many practical applications of UV
radiation derive from its interactions with
organic molecules.

16. UVC
• UVC is the most dangerous type of ultraviolet
light but cannot penetrate earth's protective
ozone layer. Therefore, it poses no threat to
human, animal or plant life on earth.

17. UVA & UVB
• UVA and UVB, on the other hand, do
penetrate the ozone layer in attenuated form
and reach the surface of the planet. UVA is
weaker than UVB but passes further into the
skin than UVB. It is now generally accepted
that both UVA and UVB cause skin cancer,
including melanoma. For this reason,
sunscreens are recommended that block both
kinds of radiation -- UVA and UVB.

18. THANK YOU