Dipole Orientation Distributions in Langmuir−Blodgett Films by Planar Waveguide Linear Dichroism and Fluorescence Anisotropy

Abstract

A method to determine the orientation distribution of fluorescent molecules in a thin, substrate-supported film is described. Attenuated total reflection spectrometry on the surface of a planar waveguide is used to measure absorption LD, from which the mean dipole tilt angle in the film is obtained. Steady-state fluorescence anisotropy is measured in a total internal reflection geometry on a film supported on fused silica but prepared under otherwise identical conditions. The angular distribution about the mean can be recovered from the anisotropy measurement by modeling the distribution as a probability density that is specified by two adjustable parameters. The method was tested on Langmuir−Blodgett (LB) films of arachidic acid doped with the fluorescent amphiphiles DiI and BODIPY. In the DiI-doped films, the mean tilt angle was 75° from the surface normal. Assuming a Gaussian distribution, the standard deviation was 12°, indicating a high degree of macroscopic order. In the BODIPY-doped films the distribution was 59 ± 17°, which indicates a less ordered assembly. Larger angular distributions were calculated using a step function model. The results show that dipoles in the headgroup region of arachidic acid LB films are more ordered than dipoles in the alkyl chain region. The method should prove useful in studying relationships between assembly technique, structure, and function in two-dimensional molecular arrays.

Local orientations of fluctuating fluid interfaces

“…Izy+Iyy +Iyx [35], where the emission intensity I ij results from an excitation polarized along the i-axis and measured along the j-axis. Assuming that the absorption and emission dipoles are colinear and that the emission intensity is proportional to the projection of the dipole onto the detection plane, the measured decay of the anisotropy is given typically by r(t) = (r(0) − r(∞))e −t/τ + r(∞) (see Refs.…”

“…Assuming that the absorption and emission dipoles are colinear and that the emission intensity is proportional to the projection of the dipole onto the detection plane, the measured decay of the anisotropy is given typically by r(t) = (r(0) − r(∞))e −t/τ + r(∞) (see Refs. [35,36,37]) and…”

Development of Tetrahydrofuran/Water Optical Waveguide and Its Application to the Observation of Extraction Behavior of l-Anilino-8-naphtalene Sulfonate at the Tetrahydrofuran/Water Interface

“…Integrated optical waveguides of planar type have most widely been applied for these purposes. [6][7][8] Besides those waveguides, liquid/liquid optical waveguides (LLWs), which have a liquid-core/liquid-cladding structure, have firstly been proposed by our group. [9][10][11][12][13] LLWs have been formed with sheath flow of liquids from concentric glass capillaries into an outer glass capillary.…”

Probing single molecule orientations in model lipid membranes with near-field scanning optical microscopy

“…7,8 Typically, measurements of molecular orientation are carried out on large ensembles where the sample is required to have a high degree of long range order. [9][10][11][12][13][14] These types of bulk measurements average across the specific distribution of individual molecules which can hide important sample details. The single molecule orientation sensitivity of NSOM combined with its high spatial resolution fluorescence and force imaging capabilities, therefore, provide a powerful new tool for many applications.…”