Regular Two-Dimensional Arrays of Surface-Mounted Molecular Switches: Switching Monitored by UV–vis and NMR Spectroscopy

Using solid-state 15N
NMR spectroscopy, the cis/trans isomerization
in a two-dimensional
(2-D) array of surface-mounted azobenzene-based switches was detected
for the first time. In order to achieve this, a new class of rod-shaped
molecular switches, suitable for formation of 2-D regular arrays on
large facets of tris­(o-phenylenedioxy)­cyclotriphosphazene
(TPP) nanocrystals, was synthesized. A mechanochemical approach was
used to prepare corresponding host–guest surface inclusions
in a TPP matrix. Comparison of thermal steps in solution and supramolecular
surface inclusions revealed that switching of individual molecules
is not compromised by the close proximity of neighbors.

本研究首次借助固态15N核磁共振波谱法（solid-state 15N NMR spectroscopy），在表面固定偶氮苯基分子开关（azobenzene-based switches）的二维（2-D）阵列中成功检测到顺反异构化过程。为达成该观测目标，我们合成了一类新型棒状分子开关（rod-shaped molecular switches），这类开关可在三(邻苯二氧基)环三磷腈（tris(o-phenylenedioxy)cyclotriphosphazene, TPP）纳米晶体的大晶面上形成规整二维阵列。本研究采用机械化学法（mechanochemical approach），在TPP基质中制备了对应的主客体表面包合物（host–guest surface inclusions）。通过对比溶液体系与超分子表面包合物（supramolecular surface inclusions）的热致转变步骤，研究发现单个分子的开关行为并未因相邻分子的紧密排布而受到阻碍。