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Photochemistry Research Unit,
Regional Research Laboratory, CSIR Trivandrum 695 019
Photochemistry
Photochemistry deals with the chemical and physical transformations of matter
brought about by its interaction with light. Photochemical processes play a key role in a number of
naturally occurring processes, such as photosynthesis, vision and formation or depletion of ozone in the upper atmosphere.
Traditionally photochemistry has played an important role in a variety of imaging applications such as photography,
xerography and photolithography. Enormous strides have been made in our understanding of
the fundamental aspects of photochemical reactions in the past few decades, with the help of sophisticated instrumentation
such as pulsed lasers and sensitive detectors. Fairly good molecular level
descriptions of the primary processes in photosynthesis and vision for example are now available. This
understanding has lead to rapid advances in photonics or photon based technologies. Apart from imaging, modern applications of
photonics now exist in areas as diverse as medicine, environment, solar energy harvesting, communications,
entertainment, electrooptics and optical computing. An example where photon based technologies have made
significant impact is in the area of medicine. Photodynamic therapy, which involves the use of lasers in combination with
suitable photosensitizers, has been developed as a method for treatment of certain types of cancers. It has considerable
advantages over some of the conventional methods such as chemo- and radiation-therapy. Photodynamic
methods are being developed for disinfecting blood and blood products. This has
enormous implications in the treatment of infected blood received in blood
banks. Based on similar principles, methods are being developed for the large-scale sterilization of sewage
water. Photocatalytic methods are also being developed for detoxification of industrial effluents.
Energy is another area where recent developments in photochemistry are going to have a major impact.
With the ever rising cost as well as the depletion of fossil fuels, need for
funding alternative sources of energy is becoming imperative. The use of
a-Si based photovoltaics has been prohibitive in terms of cost due to the need for growing high purity semiconductor crystals. By mimicking
the basic photochemical processes in photosynthesis, artificial devices, which
are cost effective, can be designed for harvesting solar energy. Recent developments on dye sensitized photoelectrochemical cells which utilize
amorphous semiconductors such as titanium dioxide indicate that low-cost
solar cells could soon be available. Imaging technologies are undergoing a major revolution. The availability of
low cost semiconductor lasers emitting in the near infrared region (700-1100
nm) and photosensitizers that can absorb in this region have led to the development of optical and laser discs which can deliver high quality video
pictures and sound. Compact discs, which deliver digital sounds, are also
available. These devices are capable of recording and reproducing information in high density and may replace completely the existing magnetic
storage devices in the near future. Improved methods of photopolymerization
and new developments in photoactive liquid crystals can lead to significant
improvements of advanced imaging techniques such as holography. Recent advances in nonlinear optical and photorefractive materials, light
emitting polymers and photoswitchable materials can contribute to the development of photon based technologies for application in areas such as
telecommunication and defense. Research in such materials can also lead to
future technologies such as optical computers, which can operate at time
scales of three orders of magnitude higher than the present day computers.
The Photochemistry Research Unit
Established in 1989, at and as a part of the Regional Research Laboratory,
CSIR, Trivandrum, the Photochemistry Research Unit has evolved into a multidisciplinary group with expertise in physical,
organic, polymer and bio-related aspects of photochemistry. At present the research interests of the
Unit can be categorized as (i) study of photoinduced electron transfer process
and (ii) development of organic materials for photonic applications. The group
has made significant contributions in each of these areas.
(i) Photoinduced Electron Transfer
Photoinduced electron transfer forms the key step in important
photoprocesses, such as in photosynthesis and several photoimaging applications. In these processes, light absorption leads to the
formation of oxidized and reduced states, which have to be effectively separated for light energy to be
converted to electrical energy or be stored as chemical energy. The work carried out by the Unit in this
area is mainly concerned with understanding the factors that affect the primary processes and to device
methods for improving the efficiency of charge separation.
(ii) Organic Materials for Photonic Applications
The group has contributed significantly towards developing new materials and understanding the
structure property relationships of materials with regards to a variety of photonic applications. The
materials being developed or investigated include;
a) near infrared absorbing/fluorescing dyes,
b) photoactive liquid crystals,
c) fluorescent sensors for detection of metal ions and other species of biological
relevance,
d) photo- and electroluminiscent polymers,
e) photosensitizers for biomedical applications
f) metalic and semiconductor nanoclusters
Vision for the Photochemistry Research Unit.
The long-term goal of the Photochemistry Research Unit is to emerge as a Centre for Photonics
Research, with expertise in chemistry, physics and engineering. Such a multidisciplinary approach
would be essential for converting basic research ideas into technologies. The Wellman Laboratories of
Photomedicine at Harvard and the Center for Photonics Research at Boston University are few of the
institutions, which have developed successfully along these lines. The basic objectives of such a Centre
would be:
Ø Establish and maintain laboratory facilities for advanced research
in photochemistry
Ø Conduct basic and applied research on photonic materials,
devices and systems
Ø Promote use of photon based technologies by sensitizing end
users such as hospitals and industry to potential applications.
Ø Commercialize photonic devices and facilitate technology transfer
Ø Prepare students for careers in photochemical sciences
Areas where the Photochemistry Research Unit can make an impact in the coming years
with a sustained effort and suitable support, the Photochemistry Research Unit can make
significant contributions in the following areas:
Energy:
Development of artificial systems capable of mimicking the photoinduced charge separation of
photosynthesis. Based on such systems, devices capable of harvesting solar energy in an economically
viable method could be developed.
Environment:
Development of methods using sunlight in combination with photocatalyst for large scale
disinfection and detoxification of water.
Medicine and Biology:
Development of fluorescent probes for detection of biologically important analytes and
photosensitizers for photodynamic therapy.
Imaging Technology:
Development of near infrared absorbing dyes with improved absorption and chemical stability.
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