Long‐Lived Circularly Polarized Phosphorescence in Helicene‐NHC Rhenium(I) Complexes: The Influence of Helicene, Halogen, and Stereochemistry on Emission Properties

Abstract

The first enantiopure chiral‐at‐rhenium complexes of the form fac‐ReX(CO)3(:C^N) have been prepared, where :C^N is a helicene‐N‐heterocyclic carbene (NHC) ligand and X=Cl or I. These have complexes show strong changes in the emission characteristics, notably strongly enhanced phosphorescence lifetimes (reaching 0.7 ms) and increased circularly polarized emission (CPL) activity, as compared to their parent chiral models lacking the helicene unit. The halogen along with its position within the dissymmetric stereochemical environment strongly affect the photophysics of the complexes, particularly the phosphorescence quantum yield and lifetime. These results give fresh insight into fine tuning of photophysical and chiroptical properties of Re‐NHC systems.

Beyond Chiral Organic (p-Block) Chromophores for Circularly Polarized Luminescence: The Success of d-Block and f-Block Chiral Complexes

“…More recently, the complex 43 was obtained through the coordination of a helicenic ligand to a Re I metal center with intrinsic achiral coordination sphere (Saleh et al, 2015b ). Although this straightforward method provides enantiopure complexes, the associated dissymmetry factors remain weak, and only few further synthesis were performed for CPL application (Gauthier et al, 2020 ). Finally ligand-centered CPL were casually tuned or switched by a closed shell d-block metal like Ag I or Au I .…”

Recent progress on NHC-stabilized early transition metal (group 3–7) complexes: Synthesis and applications

“…191 First examples of chiral-at-rhenium complexes have been prepared and fully characterized through the introduction of a chiral enantiopure NHC-helicene of the form fac-ReX(CO)3(NHC) 167. 192 These compounds exhibit strong chiroptical activities, especially intense circularly polarized phosphorescence and also phosphorescence lifetimes that are > 4000 times longer than other NHC and helicene-based rhenium complexes (up to 0.7 ms). .…”

Bright Long‐Lived Circularly Polarized Luminescence in Chiral Chromium(III) Complexes

“…Thus,l arge g lum and high quantum yields should be concomitantly increased to rise B CPL ,w hich is rather challenging since it is common to observe large g lum values accompanied by low luminescence efficiencies. [12] Major activity in this field is currently focused on the development of chiral materials including organic dyes, [13][14][15][16][17] 3d, 4d and 5d complexes, [16][17][18] and lanthanides complexes. [19][20][21] Thet wo former systems are not particularly promising for maximizing g lum because of the weak magnitude of the magnetic dipole compared to electric dipole transition moment (j m j 2 % 75 000 j m j 2 ) [22] but usually provide high luminescence brightness (e lexc f)associated with allowed charge transfers (metal-to-ligand charge transfer or ligand-to-metal charge transfer) and p*!p transitions.Despite their low g lum , some strategies such as encapsulation of organic molecules into chiral liquid crystals, [23] formation of intramolecular excimers, [24,25] molecular aggregation, [26,27] synthesis of cyclic aromatic structures, [28] or supramolecular assemblies [29] and phenomena such as Fçrster resonance energy transfer (FRET), [30][31][32] or triplet-triplet annihilation (TTA)-based upconversion [33,34] could provide large dissymmetry factor in these materials.…”