Molecular engineered rhenium(i) carbonyl complexes to promote photoisomerization of coordinated stilbene-like ligands in the visible region

Abstract

Novel fac-[Re(CO)3(dmcb)(trans-stpyR)]+ complexes, dmcb = 4,4'-dimethoxycarbonyl-2,2'-bipyridine, have been judiciously engineered to absorb at lower energies and sensitize trans-4-styrylpyridine (trans-stpy) or trans-4-(4-cyano)styrylpyridine (trans-stpyCN) photoisomerizable ligands up to 436 nm of irradiation. Moreover, these complexes exhibit remarkable photoreversibility, in particular fac-[Re(CO)3(dmcb)(trans-stpyCN)]+ (Φ255 nmcis→trans = 0.26 ± 0.02). Their distinct and noteworthy photochemical and photophysical behavior are described in this work. The main emphasis of this study is that the complexes efficiently sensitize stilbene-like ligand isomerization toward use in potential solar device applications.

Spectroscopic Study of the E/Z Photoisomerization of a New Cyrhetrenyl Acylhydrazone: A Potential Photoswitch and Photosensitizer†

“…For example, fac ‐tricarbonyl Re(I) fragments have been used to promote the photoisomerization of stilbene‐like and azobenzene ligands in the visible spectral region (29‐34). These compounds showed a remarkable cis ⇌ trans photoreversibility with quantum yield values as high as Φ trans→cis = 0.17‐0.65 range and Φ cis→trans = 0.16‐0.26 range, offering a new strategic approach to designing molecular switches (32,33).…”

“…The singlet MLCT excited state ( 1 MLCT) undergoes a fast intersystem crossing to the triplet excited state ( 3 MLCT) (27), which can transfer its energy to a triplet intraligand excited state ( 3 IL) localized on the photoswitchable fragment, finally producing a photoisomerization reaction (28). For example, fac-tricarbonyl Re(I) fragments have been used to promote the photoisomerization of stilbene-like and azobenzene ligands in the visible spectral region (29)(30)(31)(32)(33)(34). These compounds showed a remarkable cis ⇌ trans photoreversibility with quantum yield values as high as Φ trans?cis = 0.17-0.65 range and Φ cis?trans = 0.16-0.26 range, offering a new strategic approach to designing molecular switches (32,33).…”

Visible Photosensitization of trans-Styrylpyridine Coordinated to fac-[Re(CO)3(dcbH2)]+: New Insights

“…The coordination of trans -stpy to fac -[Re­(CO) 3 (dmcb)­Cl] shifts trans -stpy hydrogen signals to lower δ and dmcb hydrogen signals to higher δ because of the magnetic anisotropy from the ring-current effect . As is typically observed for fac -[Re­(CO) 3 (NN)­( trans -L)] + complexes, trans -stpy deshields the hydrogen atoms of dmcb, while dmcb shields the hydrogen atoms of trans -stpy. ,,,,,, The hydrogen coupling constant between H c and H d ( J 3 ≈ 16 Hz) is characteristic of trans -olefin isomers. ,,, …”

“…The photoisomerization of rhenium­(I) carbonyl complexes with stilbene-like ligands has been investigated extensively, − with a special focus on compounds that extend their absorption to the visible to create photochemical and photophysical properties suitable for applications in molecular devices. ,,,,, These studies, and an understanding of their properties, allow modulation and control of key roles into the development of photoinduced devices, such as photosensitizers, photoswitches, and photoresponsive devices. ,,− …”

“…Coordination also improves the versatility and variety of synthetic tools that can be conveniently employed to design new compounds with desired characteristics to tune excited-state properties through changes in polypyridyl and photoisomerizable ligands . As a result of a series of studies, the best results reported so far achieved up to 404 nm sensitization, but usually with a lower quantum yield. ,,− ,, Only recently, our group succeeded in synthesizing new complexes fac -[Re­(CO) 3 (dmcb)­( trans -stpy)] + and fac -[Re­(CO) 3 (dmcb)­( trans -stpyCN)] + [dmcb = 4,4′-dimethoxycarbonyl-2,2′-bipyridine, trans -stpy = trans -4-styrylpyridine, trans -stpyCN = trans -4-(4-cyano)­styrylpyridine], which are capable of initiating photoisomerization in a lower-energy spectral region …”