Assigning Optical Absorption Transitions with Light-Induced Crystal Structures: Case Study of a Single-Crystal Nanooptomechanical Transducer

Abstract

UV/vis absorption spectroscopy affords indirect structural information about the photochemistry and photophysics of molecules by inferring types of electronic transitions from spectral features. Direct structural information would become available, though, if light-induced crystal structures could be mapped against changes in optical absorption spectra as a photochemical process evolves. We present a series of light-induced crystal structures that track real-time changes in solid-state optical absorption spectra of a crystalline nanooptomechanical transducer, while the transduction process unfolds within its crystal lattice at 100 K. Results afford a combined structural and spectral mapping of its solid-state optical absorption, from which the operational mechanism of nanooptomechanical transduction is revealed. Metal-to-ligand and metal-centered charge-transfer bands are assigned to optical absorption peaks directly from their three-dimensional (3D) light-induced crystal structures. This approach could be used to characterize many solid-state optoelectronic materials.

Structural Capture of η1-OSO to η2-(OS)O Coordination Isomerism in a New Ruthenium-Based SO2-Linkage Photoisomer That Exhibits Single-Crystal Optical Actuation

“…130 min, whereby this absorption essentially becomes saturated, as shown by its minimal further increase up to a total light-exposure time of 240 min. This sequence of changes in the single-crystal optical-absorption spectra of 1 is likewise observed in its bromo 44 and iodo 46 analogues, although the exact wavelengths and optical-absorption values differ between these studies. Such a trend is similarly observed in the 3-methylpyridine analogue of these [RuSO 2 ] complexes that also behave as a nano-optomechanical transducer.…”

“…While this photoconversion fraction is not unusual in the wider set of [RuSO 2 ] complexes, it contrasts markedly to the situation with its bromo and iodo analogues, which exhibit 100% photoconversion. 44 , 46 It should be noted that this particular comparison was not extended to the chloro analogue, as its photocrystallography results were produced using a different (white) light source, 38 cf. a 505 nm LED source was used to study the other 3-halopyridine-based complexes.…”

“…Only a small extent of arene rotation was observed in 1 within the tosylate anions that are engaged in nano-optomechanical transduction in the light-induced crystal structures of trans -3-halopyridine-based [RuSO 2 ] complexes. The SO 2 -linkage photoisomerization process caused this arene ring to rotate by 39(4), 68(3), and 77(3)° in the chloro, 38 bromo, 44 and iodo-based 46 complexes, respectively; in contrast, this rotation is too small to be quantified in the light-induced crystal structure of 1 ; it is observable by comparing the ADPs of the carbon atoms in this ring, especially C21, C22, C24, and C25, either between those of the dark-state and light-induced crystal structures or comparing these ADPs against those of the other anion in the light-induced crystal structure (i.e., C11, C12, C14, and C15). For example, the ADPs of carbon atoms in the nonrotor ring of 1 (anion 2) are pretty isotropic when viewed edge-on in its light-induced crystal structure ( Figure 1 , top right) while the carbon atoms in the rotor ring of 1 (anion 1) can be seen to be distinctly anisotropic along the direction of the crystallographic a axis, as shown in Figure 1 (bottom).…”

“…Both of these complexes were found to exhibit nano-optomechanical transduction with 100% η 1 -OSO photoisomer formation. 44 , 46 This 100% SO 2 photoconversion is important because it opens up real-world opportunities for these materials in solid-state device technologies, where clean photoswitching is a prerequisite for many photonic applications; only fractional SO 2 photoconversion levels have been realized in all other [RuSO 2 ] complexes, as well as many other linkage photoisomers in other types of compounds that have been reported to date.…”

“…As well as being the first [RuSO 2 ] complexes to show 100% SO 2 photoconversion, results on trans -[Ru(SO 2 )(NH 3 ) 4 (3-bromopyridine)]tosylate 2 44 and trans -[Ru(SO 2 )(NH 3 ) 4 (3-iodopyridine)]tosylate 2 46 are significant because they complement those of [Ru(SO 2 )(NH 3 ) 4 (3-chloropyridine)]tosylate 2 38 to form a series of photocrystallographic results on [Ru(SO 2 )(NH 3 ) 4 (3-halopyridine)]tosylate 2 complexes. In turn, these results naturally beg the question as to how the remaining complex in this halogen series behaves.…”