Understanding solid-state photoswitching in [Re(OMe₂-bpy)(CO)₃(η¹-NO₂)] crystals via in situ photocrystallography

Abstract

Single-crystal-to-single-crystal nitro → nitrito isomerism is reported for the novel rheniumIJI)-bipyridine complex [ReIJOMe 2 -bpy)IJCO) 3 IJη 1 -NO 2 )], achieving a maximum conversion of 66% to a photoinduced nitrito-(η 1 -O _NO) isomer under continuous illumination. The 3D X-ray structure of the photoinduced isomer is determined by steady-state and psuedo-steady-state photocrystallographic methods, providing insight into the structural changes required to accommodate photoswitching. Photocrystallographic kinetic studies follow the progress of photoswitching with time, determining a reaction rate constant of k = 0.38(2) min −1 at 150 K. Linkage isomerism is fully-reversible on warming, and pseudo-steady-state experiments confirm that the photoexcited state is retained, at measurable occupancy, up to a temperature of 240 K. These results confirm the validity of combining photoactive linkage isomer and ReIJI) photocatalyst chemistries, and the detailed determination of the photoexcited state structure will facilitate the future design of new photoactive ReIJI) crystals for a range of applications.5990 | CrystEngComm, 2018, 20, 5990-5997 This journal is Fig. 1 Single-crystal X-ray structure of the GS of 1 at 150 K. (a) Atomic connectivity in the asymmetric unit, ellipsoids at 50% probability, hydrogen atoms removed for clarity; (b) crystal packing arrangement; (c) C-H⋯O interactions involving the nitro-NO 2 ligand. CrystEngComm Paper

Exploring the influence of polymorphism and chromophore co-ligands on linkage isomer photoswitching in [Pd(bpy4dca)(NO2)2]

“…An increase in the unit cell volume of 1.93% was found on excitation, which is a fairly large change compared with other photoactive linkage isomers. 36,38,43,45 The excitation profiles for both ligands in Fig. 4(b) are sigmoidal, as seen for similar linkage isomer crystals.…”

“…An increase in the unit cell volume of 1.93% was found on excitation, which is a fairly large change compared with other photoactive linkage isomers. 36,38,43,45…”

“…A moderate increase of 0.93% in the unit cell volume between the GS and photostationary ES was observed, which is considerably smaller than that seen for form II and is more in-line with other nitrite linkage isomers that display incomplete photoswitching in the single-crystal. 43,45 The excitation profiles for all four nitrite ligands were fitted to the JMAK model, providing kinetic information (Fig. 6).…”

“…Anecdotal evidence from our research over the last 10 years indicates that compounds having co-ligands with extended pi-systems (bipyridine, biquinoline, phenanthroline etc. ) led to crystals with lower, 43 or even no photoswitching capability under the typical conditions used by us to study linkage isomers of this type ( e.g. T = 100–150 K, λ = 390–450 nm).…”

Uncovering the role of non-covalent interactions in solid-state photoswitches by non-spherical structure refinements with NoSpherA2

“…21 The LED wavelength used varied for the sample under study according to their solid-state absorption profiles and was chosen in-line with previous literature. 16,18,22 For all samples, the crystal was rotated about the φ-axis during the illumination period, to ensure even illumination across its bulk.…”