Two orientations and photochromism of polyelectrolyte/bacteriorhodopsin alternative deposition multilayers

A series of organized multilayers have been formed by the alternative adsor ption of positively charged poly(dimethyldiallylammonium chloride) (PDAC) a nd purple membrane (PM) fragments in suspensions at pH = 4-11. Both UV-vis spectrophotometry and quartz crystal microbalance (QCM) technique were used to monitor the deposition process of PDAC/bacteriorhodopsin (bR) multilaye rs, suggesting that PM fragments and PDAC are deposited alternatively on th e substrate uniformly, Upon illumination, all these multilayers generate ph otovoltages with defined signs. The negative sign of photovoltage accompany ing the formation of M-state at pH < 7 indicates that the extracellular sid e of PM fragments is directed toward the substrate; and the positive sign a t pH greater than or equal to 7 indicates that the cytoplasmic side of PM f ragments is directed toward the substrate. In addition, the long-lived mult iple M-state has been observed in all multilayer films. Moreover, M-state a t high pH, which shows the longer lifetime than that at low pH, decays into the ground state (B) completely in 30 min.