ABSTRACT
Life means energy consumption and has for over 4 billion years on earth. The only energy has come from the sun, and porphyrins constituted its major chemical link to the earth. Chemists began to learn slowly from natural photosynthesis and tried to split water into hydrogen and oxygen using the sun's radiation as an energy source. Porphyrin chemistry may be a good starting point.The dominating porphyrin derivative in photosynthesis is chlorophyll a, which provided the optimal chromophore for sunlight absorption as well as its conversion to chemical energy. Its spectrum fitted the emission spectrum of the sun on the earth ~s surface (chlorophylls a,b) or in water (bacteriochlorophylls, various bile pigments in algae); the photochemically excited states reversibly release electrons, yielding stable radicals. The chemical energy of these radicals is then bundled and migrates into the most abundant substance on earth, namely water, which is split into hydrogen and oxygen. This mixture of gases is the most useful and harmless chemical means of storing energy because the combustion product is again water.
