Systems Approach of Photoisomerization Metrology for Single-Crystal Optical Actuators: A Case Study of [Ru(SO₂)(NH₃)₄Cl]Cl

Abstract

Chemicals that undergo photoisomerization in their single-crystal form may act as optical actuators or sensors. It is important to determine the molecular-scale characteristics of this photoisomerization as they govern the macroscopic nature of the optical phenomenon. In situ single-crystal X-ray diffraction has led the way in this field of characterization, with photoinduced crystal structures being realized via technical developments that have become known as "photocrystallography". Single-crystal optical spectroscopy methods are less well developed in this research area, even though they provide synergistic information that is crucial for optimizing photoconversion levels in single-crystal optical actuators and enabling their comprehensive photoisomerization analysis. This paper demonstrates the importance of characterizing photoisomerism in crystalline media using a systems approach to photoisomerization metrology. Therefore, single-crystal optical spectroscopy, single-crystal Raman spectroscopy, and photocrystallography are concerted. The case study on [Ru(SO 2 )(NH 3 ) 4 Cl]Cl (1) shows how this approach optimizes its photoconversion levels, using key parameters that are established by single-crystal optical absorption spectroscopy. These parameters furnish the design of single-crystal Raman spectroscopy and photocrystallography experiments which are needed for a comprehensive photoisomerization analysis of 1. Raman shifts identify photostructural changes in isolated bonds as a function of temperature. One such shift leads to the realization of a previously unidentified photoisomer in 1, which is then confirmed by photocrystallography that renders its 3-D light-induced crystal structure. Both optical-spectroscopy methods are concerted with imaging to evidence photochromic changes in single crystals that occur upon photoisomerization and upon their thermal decay, whose characteristics are realized via single-crystal Raman spectroscopy. Overall, an end-to-end operational pipeline is showcased for more optimally characterizing the light-induced optical properties and structures of single-crystal optical actuators.

Low-energy optical switching of SO2 linkage isomerisation in single crystals of a ruthenium-based coordination complex

“… 12–20 Given this history of η 1 -OSO photoisomers in similar complexes, and that the subtle and complex nature of light-induced SO 2 disorder within these [RuSO 2 ] compounds could potentially mask other minor photoisomeric components, single-crystal Raman spectroscopy of 1 was employed. This served as an independent check that the current photocrystallography study has not missed any evidence for the existence of a η 1 -OSO photoisomer at 100 K. The spectroscopy corroborated our photocrystallography results, as judged by the absence of a Raman shift at 595 cm −1 at 90 K in 1 (see ESI † ), a peak that has been attributed to this η 1 -OSO photoisomeric species in the closely related coordination complex, trans -[Ru(SO 2 )(NH 3 ) 4 Cl]Cl, at 90 K. 27 …”

“…These series of experiments largely followed the optical spectroscopy methodologies that have been developed by Cole et al to support photocrystallography. 27 The reader is referred to Experimental methods for specific technical detail about the measurements conducted herein.…”

“…A more detailed description of this custom instrument set up and its operational pipeline, as provisioned to support photocrystallography, is given elsewhere. 27 …”

Molecular engineering of single-crystal optical actuators

“…One possible material option is a series of compounds based on the generic formula, [Ru(SO2)(NH3)4X]Y, whose SO2 group manifests solid-state linkage photo-isomerization (X is the trans-ligand to SO2; Y is a counterion). This light-induced phenomenon causes these materials to act as photo-induced molecular switches [6][7][8][9][10][11][12] or molecular transducers [13][14][15][16][17]. This talk will present the development of this family of materials towards such applications, via a range of advanced in situ light-induced x-ray diffraction (now known as photo-crystallography) [18][19][20] and in-situ light-induced single-crystal optical absorption spectroscopy microscopy experiments [11] that capture the phenomenon in their light-induced state [13][14][15].…”

“…This light-induced phenomenon causes these materials to act as photo-induced molecular switches [6][7][8][9][10][11][12] or molecular transducers [13][14][15][16][17]. This talk will present the development of this family of materials towards such applications, via a range of advanced in situ light-induced x-ray diffraction (now known as photo-crystallography) [18][19][20] and in-situ light-induced single-crystal optical absorption spectroscopy microscopy experiments [11] that capture the phenomenon in their light-induced state [13][14][15]. Results are enabling our understanding of the light-induced molecular structure and physical properties of these light-induced solid-state actuators.…”