%0 Online Multimedia
%A Kumarasinghe, Ruwandi
%A Higgins, Eric D.
%A Ito, Takashi
%A Higgins, Daniel A.
%D 2016
%T Spectroscopic and Polarization-Dependent Single-Molecule
Tracking Reveal the One-Dimensional Diffusion Pathways in Surfactant-Templated Mesoporous
Silica
%U https://acs.figshare.com/articles/media/Spectroscopic_and_Polarization_Dependent_Single_Molecule_Tracking_Reveal_the_One_Dimensional_Diffusion_Pathways_in_Surfactant_Templated_Mesoporous_Silica/2088268
%R 10.1021/acs.jpcc.5b10152.s003
%2 https://acs.figshare.com/ndownloader/files/3721483
%K mesoporou
%K NR exhibits 1 D diffusion
%K molecule emission polarization
%K surface interactions
%K dye Nile Red
%K PDI orientational motions
%K pore
%K confinement
%K NR molecules
%K SMEP
%X The efficiency and selectivity of
catalytic reactions and chemical
separations occurring in liquid-filled mesoporous materials are governed
by the translational and orientational mobilities and surface interactions
of the incorporated reagents and analytes. In earlier studies of these
phenomena by single molecule emission polarization (SMEP) methods,
perylene diimide (PDI) dyes were shown to exhibit unexpectedly strong
confinement as they diffused within the one-dimensional (1D) pores
of surfactant-templated mesoporous silica films. Restriction of PDI
orientational motions was attributed to their confinement to the most
hydrophobic regions of the micelles filling the pores. Unfortunately,
no clear evidence for the location of the dye was obtained, and its
confinement could also be explained by interactions with the pore
walls. In this report, spectroscopic single molecule tracking (sSMT)
studies using the polarity sensitive dye Nile Red (NR) are employed
to determine the location of the molecules. NR exhibits 1D diffusion,
consistent with its confinement to the cylindrical pores. The sSMT
data reveal that the majority of NR molecules are found in nonpolar
environments having polarities similar to that of n-hexane. SMEP measurements demonstrate that the NR molecules diffuse
with their long axes aligned parallel to the long axis of the pores
and that they are orientationally confined to ∼0.6 nm diameter
pathways within the pores. The diffusion coefficient for 1D diffusing
NR is also shown to be ∼103-fold smaller than in
bulk solution. Taken together, these results demonstrate that the
NR dyes are confined to the hydrophobic cores of the micelles. These
studies afford an enhanced understanding of how nanostructuring of
the pore-filling medium in solvent- and surfactant-filled mesoporous
materials governs the mass transport and surface interactions of incorporated
reagents and analytes.
%I ACS Publications