Single-Crystal Optical Actuation Generated by 100% SO2 Linkage Photoisomerization in a Ruthenium-Based Coordination Complex

Single-crystal
optical actuators are emerging as a new field of
materials chemistry because of their wide-ranging potential applications,
from light-induced molecular motors to photosensing technologies.
Ruthenium-based coordination complexes that contain sulfur dioxide
linkage photoisomers have shown particular promise as optical actuators,
given that they may exhibit either optical switching or nano-optomechanical
transduction in their single-crystal form. The type of single-crystal
optical actuation observed in a specific compound within this family
of complexes depends upon the nature of the ligand that lies trans to this SO2 linkage photoisomer, since
this governs the type and extent of photoisomer (η2-(OS)O or η1-OSO) that will form upon the application
of light. We report the discovery of a new complex, trans-[Ru­(SO2)­(NH3)4(3-iodo­pyridine)]­tosylate2 (1), which forms an η1-OSO
photoisomer with 100% photoconversion upon the application of 505
nm light. The photoisomerization process in the ruthenium-based cation
of 1 stimulates rotation and translation of the toluenic
constituent of its neighboring anion, thereby affording nano-optomechnical
transduction. We show that this η1-OSO photoisomer
transitions to its more thermally stable η2-(OS)­O
photoisomer with an activation energy, Ea, of 11(2) kJ/mol using thermally activated single-crystal optical
absorption spectroscopy. The application of external light with different
wavelengths to 1 is also shown to cause a variation in
its optical absorption spectral characteristics. This suggests that
the photophysical properties of 1 may be tunable with
light.

单晶光学驱动器因其在光诱导分子马达至光传感技术等众多领域的广泛潜在应用而崭露头角，成为材料化学领域的一门新兴学科。以钌为基础的含二氧化硫连接键的光异构配位复合物，因其单晶形式可能表现出光学切换或纳米光机械转换的特性，显示出特别的潜力作为光学驱动器。在此系列复合物中，特定化合物所观察到的单晶光学驱动类型取决于位于SO2连接键光异构体对侧配体的性质，因为这将决定在光照下形成的光异构体（η2-(OS)O或η1-OSO）的类型和程度。我们报道了一种新复合物，即trans-[Ru(SO2)(NH3)4(3-碘代吡啶)]-tosylate2（1），在施加505 nm光照射下，该复合物形成100%光转换的η1-OSO光异构体。复合物1中钌基阳离子光异构化过程刺激了其相邻阴离子甲苯基团的旋转和转换，从而实现了纳米光机械转换。我们通过热激活单晶光学吸收光谱学证实，此η1-OSO光异构体以11(2) kJ/mol的活化能（Ea）转变为更热稳定的η2-(OS)O光异构体。此外，向1施加不同波长的外部光也显示出其光学吸收光谱特性的变化。这表明，1的光物理性质可能通过光来调节。