Inorganic photoisomerization: the case study of rhenium(i) complexes

Abstract

The mechanism of photoisomerization of stilbene-like ligands coordinated to rhenium polypyridine or α-diimine carbonyls is deciphered in the light of recent theoretical results obtained at various levels of theory, density functional theory (DFT, time-dependent DFT) and state-of-the-art ab initio methods, complete active space self-consistent field (CASSCF) and multi-state CAS perturbation theory 2nd Order (MS-CASPT2). On the basis of the electronic absorption spectra and potential energy profiles (PEF) associated to the low-lying singlet and triplet intra-ligand (IL) and metal-to-ligand-charge-transfer (MLCT) excited states, coupled by spin-orbit interactions and calculated for the series [Re(CO)(3)(N,N)(L)](+) with N,N = bpy, phen and ph(2)phen (bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline; ph(2)phen = 4,7-diphenyl-1,10-phenanthroline) and L = stpy or bpe (stpy = 4-styrylpyridine; bpe = 1,2-bis(4-pyridylethylene) it is shown that the dynamics of the isomerization process are controlled by several features: (i) the occurrence of a (1)IL(L)/(1)MLCT(NN) conical intersection in the vicinity of the (1)MLCT(NN) absorption domain (ii) the kinetics of (1)MLCT(NN)/(3)MLCT(NN) intersystem crossings; (iii) the kinetics of (3)MLCT(NN)/(3)IL(L) internal conversion. The branching ratio between the two main isomerization pathways, namely along the (1)IL(L) PEF via(1)MLCT(NN)/(1)IL(L) internal conversion at the conical intersection or along the (3)IL(L) PEF after (3)MLCT(NN)/(3)IL(L) charge transfer is largely influenced by the nature of the N,N antenna and L isomerizable ligands.

Structural Properties and UV–Visible Absorption Spectroscopy of Retinal-pyridyl-CN Re(I) Carbonyl Bipyridine Complex: A Theoretical Study

“…The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 24 contrast to what has been found for stilbene-like substituted Re(I) carbonyl bpy complexes, [23][24][25] and makes competitive luminescent channels unlikely.…”

Photoreversible Molecular Motion of stpyCN Coordinated to fac-[Re(CO)3(NN)]+ Complexes

“…The intense band from 330 to 420 is assignedby comparison with precursor's spectra, Figures S16 and S17 in the Supporting Informationto an overlap between 1 MLCT Re→NN and 1 IL stpyCN transitions, similarly observed for other fac-[Re(CO) 3 (NN)(trans-L)] + complexes. 11,12,14,18,21,31,33,[36][37][38]41 The absorption spectra of the investigated complexes are blue-shifted in comparison to other fac-[Re(CO) 3 (NN)(trans-stpyCN)] + complexes with NN = phen 14 or ph 2 phen 31 (i.e., 1 MLCT Re→dmb > 1 MLCT Re→bpy > 1 MLCT Re→phen > 1 MLCT Re→ph2phen ) as the electron-withdrawing stabilization of π* NN orbitals is less pronounced for NN ligands. Furthermore, bipyridyl ligands have lower oscillator strengths than phenanthroline ligands, 14,31 leading to overall lower molar absorptivities for complexes 1 and 2.…”

“…Usually, trans -stilbene like ligands ( trans -L) exhibit a trans -to- cis photoisomerization in the UV region via 1 π → π* trans ‑L excited states. , The coordination of trans -L to Re­(I) extends the photoisomerization pathways to the visible, mainly via metal-to-ligand charge transfer ( 1 MLCT/ 3 MLCT) photosensitizations of the intraligand ( 3 IL trans ‑L ) 3 π → π* trans ‑L state. ,− The trans - cis photosensitization of such ligands have been successfully exploited in the photoregulation of DNA hybridizations as well as in the conversion of light into mechanical motion , and the search for new efficient trans - cis photosystems is a key element toward the development of molecular machines.…”

Electronic and Photophysical Properties of [Re (L)(CO)3(phen)]+ and [Ru(L)2(bpy)2]2+ (L = imidazole), Building Units for Long-Range Electron Transfer in Modified Blue Copper Proteins

“…The mechanism of photoinduced electron transfer through Re I -modified Pseudomonas aeruginosa Azurins has been deciphered by means of time-resolved spectroscopic measurements (fs to ns) and macromolecular X-ray crystallography. − The role of the low-lying singlet and triplet excited states of the inorganic chromophore in Re I (dmp)­(CO) 3 (His124)­(Trp122)­AzCu I at the early stage of the process corresponding to 1 MLCT→ 3 CS ultrafast decay (MLCT: metal-to-ligand-charge-transfer; CS: charge separated) either via the lowest 3 MLCT delocalized on dmp (500 ps), or directly via the 1 CS state delocalized on Trp (<1 ps) has been put in evidence by means of time-resolved infrared and luminescence spectroscopies . Likewise a number of recent experimental − and theoretical studies performed on Re­(I) α-diimine carbonyls substituted by a variety of ligand L ranging from halides and imidazole to isomerizable ligands have pointed to the importance of ultrafast excited states processes and spin–orbit effect in this class of molecules. − …”