Photoinduced electron transfer is the primary event in photosynthesis that is responsible for converting the light energy of the sun to chemical energy. In our group we use ruthenium trisbipyridyl based donor-acceptor systems in unique environments to mimic this process.  Understanding the mechanism of electron transfer in these reactions is important for devising systems that can efficiently split water into oxygen and hydrogen by solar energy conversion.
        In the Dutta group, I am responsible for the above-mentioned mechanistic studies using various spectroscopic techniques. We routinely use absorption, emission and laser flash photolysis techniques in the investigation. For soluble donor and acceptor molecules, transmission experiments are used and for light scattering suspensions diffuse reflectance experiments are used. In our lab, I recently completed the setup and LabView computer interfacing of a nanosecond laser flash photolysis system that can measure transient absorption spectra and kinetics in both solution state and diffuse reflectance mode with minimum reconfiguration. It can also be used for laser-induced fluorescence experiments in the transmission and diffuse reflectance mode. Currently, spectroscopic studies of various donor-acceptor systems synthesized in our lab are under progress. Some of the questions we try to answer are the nature of the transient intermediates involved and the speeds of the forward electron transfer as well as the energy wasting back electron transfer (BET). For a light harvesting system to be efficient, forward electron transfer has to be fast and BET has to be slow. We design unique light harvesting systems that can satisfy these conditions.
        Ultrafast spectroscopic techniques are essential in the case of systems where the donor and acceptor are in close proximity resulting in ultra short transient lifetimes. Our zeolite-encapsulated light harvesting system comes under this category. I use the facilities in the Center for Chemical and Biological Dynamics of our department to carry out time resolved experiments in the femtosecond and picosecond time scale. I will soon undertake the modification of an existing femtosecond pump-probe spectrometer to make it ready for carrying out diffuse reflectance experiments.                  

 

1.  The efficient synthesis of porphyrin-containing, benzoquinone-terminated, rigid polyphenyl dendrimers G. J. Capitosti, C. D. Guerrero, D. E. Binkley, Jr., C. S. Rajesh, and D. A. Modarelli J. Org. Chem. 68, 247-261 (2003) 

2.  Photophysical characterization of free-base N-confused tetraphenylporphyrins J. P. Belair, C. J. Ziegler, C. S. Rajesh and D. A. Modarelli J. Phys. Chem. A, 106, 6445-6451 (2002)

3.  Photoinduced electron-transfer within free base and zinc porphyrin containing poly(amide) dendrimers C. S. Rajesh, G. J. Capitosti, S. J. Cramer and D. A. Modarelli J. Phys. Chem. B, 105, 10175-10188 (2001)

4.  Photoinduced electron transfer within porphyrin-containing poly(amide) dendrimers G. J. Capitosti, S. J. Cramer, C. S. Rajesh and D. A. Modarelli Organic Letters; 3, 1645-1648 (2001)

5.  Transient absorption probe of intermolecular triplet excimer of naphthalene in fluid solutions: identification of the species based on comparison to the intramolecular triplet excimers of covalently-linked dimmers X. Wang, W. G. Kofron, S. Kong, C. S. Rajesh, D. A. Modarelli and E. C. Lim J. Phys. Chem. A, 104, 1461-1465 (2000)
 
6.  p-Hydroxyphenacyl phototriggers: the reactive excited state of phosphate photorelease P. G. Conrad, II, R. S. Givens, B. Hellrung, C. S. Rajesh, M. Ramseier and J. Wirz J. Am. Chem. Soc., 122, 9346-9347 (2000)

7.  Kinetics and mechanism of phosphate photorelease from benzoin diethyl phosphate: Evidence for adiabatic fission to an -keto cation in the triplet state C. S. Rajesh, R. S. Givens and J. Wirz J. Am. Chem. Soc., 122, 611-618 (2000)

8.  Transient absorption studies on 3,6-dibromo polyvinylcarbazole and its model compounds R. Anandhi, C. S. Rajesh, S. Das and S. Umapathy J. Photochem. Photobiol. A: Chem., 106, 135-139 (1997)

9.  Photoelectron transfer induced decarboxylation of substituted carboxylic acids across a liquid/liquid interface C. S. Rajesh, T. L. Thanulingam and S. Das Tetrahedron, 53, 16817-16834 (1997)

10.  Photoinduced electron transfer reactions of amines, acid chlorides and carboxylic acids S. Das, J. S. D. Kumar, C. S. Rajesh, D. Ramaiah, K. Shivaramayya, T. L. Thanulingam and M. V. George New Horizons in Organic Synthesis, V. Nair and S. Kumar (Eds.), New Age Publishers, New Delhi, 228-235 (1997)

11.  Photorearrangements of bridgehead disubstituted dibenzobarrelene esters and lactones S. Ajayakumar, C. S. Rajesh, S. Das, N. P. Rath and M. V. George J. Photochem. Photobiol. A: Chem., 86,177-183 (1995)

12.  Photophysical and photoelectrochemical behaviour of poly(styrene co-3-(acrylamido)-6-aminoacridine) S. Das, C. S. Rajesh, C. H. Suresh, K. George Thomas, A. Ajayaghosh, C. Nasr, Prashant V. Kamat and M. V. George Macromolecules, 28, 4249-4254 (1995)

13.  Photochemical electron transfer across a liquid/liquid interface: Methylene blue sensitized decarboxylation of substituted carboxylic acids S. Das, T. L. Thanulingam, C. S. Rajesh and M. V. George Tetrahedron Lett., 36, 1337-1340 (1994)

14.  Photochemistry of triethylamine-acid chloride charge-transfer complexes S. Das, C. S. Rajesh, T. L. Thanulingam, D. Ramaiah and M. V. George Chem. Soc. Perkin Trans. 2, 1545-1547 (1994)