Figure 1.

Carotenoid electrochromic absorbance changes report the transmembrane electric field generated by the light-induced charge separation in photosystem reaction centers. (A) Flashes of light generate a membrane potential through the primary photochemical charge separation in photosynthetic reaction centers. A simplified scheme of the mechanism of electrochromism is shown (B and C), adapted from ref. 26. (B) Carotenoids in the membrane respond to the electrical field with an altered energy transition between the ground and the first excited singlet states, which results in a red shift in the visible spectrum (C). (D) Measurement of the rate of dissipation of flash-generated carotenoid absorbance shift indicates the relative ion conductance of the thylakoid membrane.