Why is the human visual system sensitive only to light of wavelengths from approximately 760 to 380 nm? An answer from thermochemistry and chemical kinetics.
The range of visible light has been explained by the knowledge available of gas-phase thermochemistry and chemical kinetics. The C, C-pi bond dissociation energy at the 11 and 12 positions of the rhodopsin complex is estimated to be approximately 37.4+/-1.5 kcal/mol. This energy is just equivalent to wavelength of the red limit of the visible light. The photons of the violet limit (approx. 75.2 kcal/mol) can break the weakest C-C and H-C bonds in important species involved in the photo-induced cis-trans isomerization cycle and can stop the visual cycle.
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Molecular Energetics Consultants, St. Petersburg, FL 33701, USA.
D006801:Humans; D007536:Isomerism; D007700:Kinetics; D008027:Light; D008956:Models, Chemical; D010775:Photic Stimulation; D020419:Photoreceptor Cells, Vertebrate / Q000737:chemistry / Q000502:physiology; D012172:Retinaldehyde / Q000737:chemistry / Q000502:physiology; D012243:Rhodopsin / Q000737:chemistry* / Q000502:physiology*; D013816:Thermodynamics; D014785:Vision, Ocular / Q000502:physiology*
D012243:Rhodopsin; D012172:Retinaldehyde