Electrochromic band shift

Thylakoid membrane as a Molecular Voltmeter and Ammeter. The antibiotic valinomycin was found in 1964 by Moore and Pressman to affect ion transport across the mitochondrial membrane. Subsequently, Pressman and coworkers proposed that valinomycin is an ionophore and acts as a mobile ion carrier across the lipid membrane [cf. sectionlll.B. above]. Since the light-induced FIAC in thylakoid membrane appears to be an electrochromic band shift in pigments produced by an electric field, Boeck and Witt °, Junge and Schmid used this unique effect to probe the effect of compounds such as the ionophore, valinmycin, on the voltage and current density generated across the membrane. 

The spectral characteristics of A [ 2 have been obtained both with optical and ESR spectroscopy. The optical spectrum exhibits band shifts near 450 and 680 nm, and a broad bleaching between 450 and 550 nm [57]. It has been suggested that the bleaching is due to the reduction of an Fe-S center and the shifts to electrochromic effects on nearby chlorophyll a molecules. The ESR spectrum however presents band of g value (2.08,1.90 and 1.78) uncharacteristic for a normal Fe-S protein [57]. The nature of X remains therefore still indetermined. 

Chromotropism in the presence of an electric field, electrochromism, has been observed for just one polysilane, the copolymer (CF3CH2CH2SiMe) -co-(ftPrSiMe)m, n m = 45 55.89 The UV band for this polymer is intensified by 50% and shifted from 294 to 299 nm, in an electric field of 10s v/m. The changes are reversible when the field is removed. Other polysilanes with polar side groups might also show electrochromic behavior, but none have been studied. 

Martin etal also used 150-/5 laser pulses but at 850-nm to excite predominantly the Qy band of the primary electron donor of Rb. sphaeroides reaction centers. The kinetics were monitored at wavelengths specific to the various pigment molecules, e.g., 1240 nm for production of P870, 545 nm for BO photoreduction, and an 805-nm absorbance decrease for BChl reduction as well as for the electrochromic shift of the BChl-absorption band in the 800 nm region (see Fig. 8). 

With regard to the red shift of the exciton band with protonation, the base forms are more suited to electrochromic devices than the green salt forms. 

All conducting polymers are potentially electrochromic in thin-film form, redox switching giving rise to new optical absorption bands in accompaniment with simultaneous transport of electronic charge and counter ions in the polymer matrix, p-doping shifts the optical absorption band towards the lower energy... 

---