Chiral Bis(oxazoline) Ruthenium Complexes with Bipyridyl‐Type N‐Heteroaromatics: Comparative Stereochemical and Photochemical Characterization of their Λ‐ and Δ‐Diastereomeric Geminate Isomers

Abstract

Diastereomeric geminate pairs of chiral bis(2-oxazoline) ruthenium complexes with bipyridyl-type N-heteroaromatics, Λ- and Δ-[Ru(L-L)(2)(iPr-biox)](2+) (iPr-biox=(4S,4'S)-4,4'-diisopropyl-2,2'-bis(2-oxazoline); L-L=2,2'-bipyridyl (bpy) for 1Λ and 1Δ, 4,4'-dimethyl-2,2'-bipyridyl (dmbpy) for 2Λ and 2Δ, and 1,10-phenanthroline (phen) for 3Λ and 3Δ), were separated as BF(4) and PF(6) salts and were subjected to the comparative studies of their stereochemical and photochemical characterization. DFT calculations of 1Λ and 1Δ electronic configurations for the lowest triplet excited state revealed that their MO-149 (HOMO) and MO-150 (lower SOMO) characters are interchanged between them and that the phosphorescence-emissive states are an admixture of a Ru-to-biox charge-transfer state and an intraligand excited state within the iPr-biox. Furthermore, photoluminescence properties of the two Λ,Δ-diastereomeric series are discussed with reference to [Ru(bpy)(3)](2+).

A Doubly Alkynylpyrene‐Threaded [4]Rotaxane That Exhibits Strong Circularly Polarized Luminescence from the Spatially Restricted Excimer

“…If this assumption is correct, we could predict that the two pyrenes are arranged or at least biased with a left-handed chirality because of the continuous bisignated Cotton effects with negative and positive signs ranging from 503 to 275 nm. [20] The Kobayashi and Kano research groups have also reported the same order of Cotton effects with two parent pyrenes encapsulated in g-CD, thus suggesting a left-handed chirality for the arrangement of the pyrenes in their inclusion complexes. The computational prediction of Cotton effects in the simulated core was performed by time-dependent density functional theory (TD-DFT) and proved to qualitatively agree with the experimental data (see Figure S12 in the Supporting Information).…”

A Doubly Alkynylpyrene‐Threaded [4]Rotaxane That Exhibits Strong Circularly Polarized Luminescence from the Spatially Restricted Excimer

“…The computational prediction of Cotton effects in the simulated core was performed by time-dependent density functional theory (TD-DFT) and proved to qualitatively agree with the experimental data (see Figure S12 in the Supporting Information). [20] The Kobayashi and Kano research groups have also reported the same order of Cotton effects with two parent pyrenes encapsulated in g-CD, thus suggesting a left-handed chirality for the arrangement of the pyrenes in their inclusion complexes. [7] The rotaxane architecture fixed a pair of alkynylpyrene molecules in a spatially restricted and asymmetrically twisted .…”