Estimation of electrochrome dyes position in the bilayer through the 2nd harmonic of capacitive current

The depth of location of electrochrome dyes RH-type in a bilayer is evaluated using the magnitudes of intramembrane field Δϕ measured by two methods: from relative change of the rate of transmembrane transport of hydrophobic ions and by means of electrostriction method based on the compensation of the 2nd harmonic of capacitive current, which is generated due to electrostriction phenomenon if sine voltage is applied to the bilayer. The experiments and theoretical analysis are conducted. Comparing the theoretical curves for Δϕ measured by the both methods and the experimental data, the depth of location was estimated as follows: 0.7–1 nm for the dyes RH-421 and RH-160, and 0.9–1.15 nm for the dye RH-237.