Local Atomic Structure in Photoisomerized Ruthenium Sulfur Dioxide Complexes Revealed by Pair Distribution Function Analysis

Abstract

SO2 linkage photoisomerization in crystalline ruthenium-based complexes has demonstrated nanophotonic phenomena such as optical switching and nano-optomechanical transduction. Molecular insights into these materials have been explored largely via the characterization of their photoinduced crystal structures via in situ single-crystal X-ray diffraction, known as photocrystallography. Photoinduced molecular disorder is present, which photocrystallography can model to the extent that it is confined within the periodic boundary of a unit cell. However, non-periodic molecular disorder is suspected to exist as well. In situ total scattering experiments were therefore carried out on finely powdered crystals of four ruthenium–sulfur dioxide complexes. Data were modeled using ‘light-minus-dark’ difference pair distribution function analysis, which afforded photoinduced structural changes exclusively. This revealed structural features that were first compared against models of photoinduced crystal structures known a priori from photocrystallography. Statistical inference was then employed, which evidenced generally good agreement between the total scattering data and the photocrystallographic models, while revealing real differences that are indicative of a structure with only a short-range order. Overall, our findings demonstrate that in situ light-induced total scattering experiments on finely powdered crystals are able to reveal the photoinduced structure. The evidence suggests that such structure could include a short-range order as well as photocrystallographic content. Our demonstration experiment offers a pathway to develop studies that capture the short-range order in linkage photoisomers, while we have outlined the procedure for testing the validity of associated structural models.

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

“…However, this conguration has been observed in 1 via a different photocrystallography study on 1 that was conducted previously at a much lower temperature (13 K); 10 moreover, h 1 -OSO congurations have been found at 100 K in other members of this [RuSO 2 ] family of complexes. [12][13][14][15][16][17][18][19][20] Given this history of h 1 -OSO photoisomers in similar complexes, and that the subtle and complex nature of lightinduced 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 h 1 -OSO photoisomer at 100 K. The spectroscopy corroborated our photocrystallography results, as judged by the absence of a Raman shi at 595 cm À1 at 90 K in 1 (see ESI †), a peak that has been attributed to this h 1 -OSO photoisomeric species in the closely related coordination complex, trans-[Ru(SO 2 )(NH 3 ) 4 Cl]Cl, at 90 K. 27 The single-crystal Raman spectroscopy results also complemented the photocrystallography results in that they evidenced a range of vibrational modes that are due to local photostructural changes in 1.…”

“…The coordination complex, trans-[Ru(SO 2 )(NH 3 ) 4 (H 2 O)]tosylate 2 , (1) is one in a family of ruthenium sulfur-dioxide based (hereaer denoted [RuSO 2 ]) materials that exhibit SO 2 linkage photoisomerisation. [8][9][10][11][12][13][14][15][16][17][18][19][20] Photocrystallography [21][22][23][24][25] studies have shown that 11.1(1)% of an h 2 -(OS)O photoisomer can be generated within the crystal structure of 1 at 90 K, 9 while 36% of the less thermally stable h 1 -OSO photoisomer can form at 13 K, albeit split over two disordered orientations with 24% and 12% photoconversion. 10 Scheme 1 illustrates these photoisomerisation processes.…”

“…Indeed, the originally reported 11.1(1)% photoconversion fraction of 1 to its h 2 -(OS)O isomer at N 2 -based cryogenic temperatures is anomalously low when compared with lightinduced crystal structures of more recently determined [RuSO 2 ] complexes. [8][9][10][11][12][13][14][15][16][17][18][19][20] We will show how almost double the photoconversion fraction of h 2 -(OS)O isomer can be achieved in 1 through this work. We then present a fundamental demonstration of the optical read and write capabilities in a singlecrystal of 1 via its display of photochromism.…”

Advances in Diffraction Studies of Light-Induced Transient Species in Molecular Crystals and Selected Complementary Techniques

“…This allows examination of relatively shorterlived species, which would otherwise relax back to the ground state. Since these two methods do not require any specific and advanced experimental setups, they have been used extensively to study structural dynamics of a variety of systems, with particular emphasis on photo-switchable materials undergoing for example photoisomerization or reversible photolysis [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46].…”

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].…”