A series of organized multilayers have been formed by the alternative adsorption of positively charged poly(dimethyldiallylammonium chloride) (PDAC) and purple membrane (PM) fragments in suspensions at pH = 4-11. Both UV-vis spectrophotometry and quartz crystal micro-balance (QCM) technique were used to monitor the deposition process of PDAC/bacteriorhodopsin (bR) multilayers, suggesting that PM fragments and PDAC are deposited alternatively on the substrate uniformly. Upon illumination, all these multilayers generate photovoltages with defined signs. The negative sign of photovoltage accompanying the formation of M -state at pH < 7 indicates that the extracellular side of PM fragments is directed toward the substrate; and the positive sign at pH⩾7 indicates that the cytoplasmic side of PM fragments is directed toward the substrate. In addition, the long-lived multiple M -state has been observed in all multilayer films. Moreover, M -state at high pH, which shows the longer lifetime than that at low pH, decays into the ground state (B) completely in 30 min.

A thin multilayer dim, formed by alternate deposition of poly(dimethyldiallylammonium chloride) (PDAC) and bacteriorhodopsin (bR) (pH=9), generated a photovoltage with defined polarities upon one flash excitation. Three time constants of 2.59 mu s, 13.64 mu s and 58.03 mu s fitting to the kinetics of photo-voltage were assigned to the decay of K, L-1 and L-2 intermediates of bR photocycle respectively. The positive photovoltage accompanying the formation of M indicated that the cytoplasmic side of PM fragments was directed toward the substrate.

The lifetime of M-state in the bacteriorhodopsin photocycle was remarkably prolonged in bR-gelatin film by using 1,4,7,10-tetraoxa-13- azacyclopentadecane (aza-15-crown-5) as chemical additive. Spectral and kinetic measurements were carried out at room temperature. It is observed that the M-state in the film has a long lifetime ((tau) 1/e) of 360s with bR/aza-15-crown-5 weight ratio of 1:3 under room conditions. To investigate the mechanism of aza-15-crown-5 on the photocycle of bR 15-crown-5 was used as chemical additive too. It was suggested that the strong complexing property towards H+ of aza-15- crown-5 played an important role in the prologation. The fitting of the M-state decay kinetics curves corresponded to a sum of three and two exponential components for bR-films using aza-15-crown-5 and 15-crown-5 as chemical additive respectively.

Bacteriorhodopsin (bR) multilayer films were successfully prepared by alternatingdepositions of cationic poly(diallyldimethylammonium chloride) (PDAC) polyelectrolyte and purple membrane (PM). The advantage of the method when compared to other thin film techniques is its simplicity to prepare large selfassembled films. The orientations of the bR molecules in the films were studied by a transient photovoltage method. The polarity of the photoresponse signals showed that in basic conditions the cytoplasmic side of PM was adsorbed onto the polyelectrolyte layer, whereas in acidic conditions the extracellular side was adsorbed onto the polyelectrolyte layer. The photocycle of the bR in the films was studied by usingthe conventional flash photolysis method. The photochemical behavior of bR in dry polycationic films was similar to that in other types of dry films and the intermediate lifetimes were almost independent of the protein orientation.