Photochemistry deals with the understanding and utilization of interaction of light with matter. Sun, the ultimate source of light, has been recognized and worshipped by various civilizations as the origin of prosperity for several centuries. Only during the last hundred years has the properties of light and the mechanism of its interaction with molecules and matter been understood and has resulted in its exploitation for the benefit of the society. Thus photochemistry and photophysics play a crucial role in our everyday life, a role not sufficiently recognized by the common person. This talk will provide examples of how ‘interaction of light with matter’ has changed the way we do things during the last five decades.
Importance of photochemistry, differences between thermal and photoreactions, units and time scale. Atoms and Molecules: Electronically excited states: electronic, vibrational and spin configurations, Born-Oppenheimer approximation, quantized vibrational levels within potential energy surfaces, spin: vectorial representation, triplets, magnetic moments due to spin and orbital motion, origin of energy difference between singlet and triplet states.
Electronic transitions: Light as an oscillating dipole, rules for electronic transitions (symmetry, overlap and spin), Frank-Condon factor, vibrational-electronic mixing (reduction of symmetry and configuration mixing), radiative transitions: absorption and emission, absorption co-efficient, radiative rates, quantum yields; fluorescence and excimer emission. Phosphorescence, examples of ISC between states of different configurations; heavy atom effect.
Three types of energy transfer, factors that control T-T and S-S energy transfer; differences between dipole-dipole and collisional transfer; importance of triplet-triplet transfer in organic photochemistry: sensitization, quenching, Stern-Volmer plot. Triplet-Triplet annihilation (upconversion); Electron transfer: Rhem-Weller equation, Marcus theory, Experimental verification of Marcus inverted region.
Photochemistry in Organized and Confined Media (Supramolecular Photochemistry): Differences between solution and organized media, characteristics of solid state, micelles, liquid crystal etc., concept of reaction cavity, examples highlighting various features of reaction cavity, effect of confined and organized environments on photophysical properties of organic molecules.
Life of a scientist is challenging and demanding as it requires to be constantly creative and innovative. On the other hand, it is really exciting and mentally satisfying. In addition, a country’s economic prosperity, to a large extent, relies on the contributions of scientists and their ability to add new knowledge that could be turned into monitory benefits for the society by engineers, physicians, businessmen and economists. This general lecture outlines the mindset required to be a successful scientist.
