Several photochemical reactions of organic compounds are occurring in nature for the evolution of life and their existence on earth. Such evolutionary processes of life have been brought about by photochemical reactions of organic molecules. Among these photochemical reactions, photosynthesis of plants, vision of animals and depletion of stratospheric ozone layer are significant. Based on these photo-induced organic reactions, several devices have been developed to meet the needs of our daily life. For example, zeolites have been used in the field of sunscreens and purification of drinking water, while porphyrin, metalloporphyrin and fullerene have been used in the building block of dyads, triads and tetrads for the harvesting of solar energy as electrical energy. Artificial photosynthesis systems have been developed for the most attracting fuel producing reaction in photolytic cleavage of water in to pollution free hydrogen fuel. Several molecular wires and molecular machines have been developed based on photo-induced electron transfer (PET) processes of supramolecules in nanotechnology.