Conformational changes and chiroptical switching of enantiopure bis-helicenic terpyridine upon Zn 2+ binding

We report the synthesis of enantiomerically pure carbo[6]helicene oligomers with buta-1,3-diyne-1,4-diyl bridges between the helicene nuclei. The synthesis of monomeric (±)-2,15-bis[(triisopropylsilyl)ethynyl]carbo[6]helicene was achieved in 25 % yield over six steps. Pure (+)-(P)- and (-)-(M)-enantiomers were obtained by HPLC on a chiral stationary phase. The dimeric (+)-(P) - and (-)-(M) -configured and the tetrameric (+)-(P) - and (-)-(M) -configured oligomers were obtained by sequential oxidative acetylenic coupling. The ECD spectra of the tetrameric oligomers displayed large Cotton effect intensities of Δϵ=-851 m cm at λ=370 nm ((M) -enantiomer). We transformed the buta-1,3-diyne-1,4-diyl bridge in the dimeric (P) and (M) oligomer by heteroaromatization into a thiene-2,5-diyl linker. Although the resulting chromophore showed reduced ECD intensities, it exhibited a remarkably strong fluorescence emission at 450-500 nm, with an absolute quantum yield of 25 %.

Section: Racemicmentioning

confidence: 93%

Helical Threads: Enantiomerically Pure Carbo[6]Helicene Oligomers

Schaack

Sidler

Trapp

et al. 2017

“…The pyridine has high affinity not only towards H + , but also towards metal cations, especially for the terpyridine, which is a good scaffold for coordination to a variety of transition‐metal centers . The inclusion of a terpyridine unit in the enantiopure bis‐helicenic terpyridine 12 enabled the Zn 2+ ‐stimulated CPL switching . The enantiopure ( M , M ) and ( P , P )‐forms of 12 displayed a W‐shaped trans disposition of N atoms in adjacent rings.…”

Section: Cpl Switching By Changing the Conformationmentioning

confidence: 99%

Circularly Polarized Luminescence Switching in Small Organic Molecules

Peng

Zhao

2019

177

110

The circularly polarized luminescence (CPL) switching is of significant interest for applications in security technologies and sensing devices. Small organic molecules (SOMs) show severala dvantages over metal complexes, supramolecular assemblies, and polymers. Therefore, the recent progress on the CPL switching in SOMs is here reviewed. The resultsa re summarized based on the strategies used to tune factors that influence the emission properties, and thus, to realize CPL switching. The strategies that have been adopted include promoting the excimer formation of fluorescent units, changing the conformation of fluorophores,t uning the electronic structure of the p-skeleton/ substituent, and modulating the intramolecular chargetransfer dynamics.[a] J.

“…By definition, g lum =2( I L − I R )/( I L + I R ), ( I =intensity of circularly polarized light) can range from −2 (when the emitted light is totally right‐circularly polarized) to +2 (the emitted light is totally left‐circularly polarized). In most cases, the g lum factors of helicenic fluorophores are in the 10 −3 –10 −4 range, similarly to those of other non‐aggregate organic molecules . In a few remarkable cases however, helicene derivatives were found to show high g lum factors, reaching values from |0.016| to | 0.035| …”

Section: Figurementioning

confidence: 86%

Helicene Monomers and Dimers: Chiral Chromophores Featuring Strong Circularly Polarized Luminescence

Schaack

Arrico

Sidler

et al. 2019

The synthesis and chiroptical properties of a series of enantiomerically pure, C2‐symmetrical carbo[6]helicene dimers are reported. Two helicene cores are connected through a buta‐1,3‐diyne‐1,4‐diyl linker or a heteroaromatic bridge and bear arylethynyl substituents at their 15‐positions. This ensures the possibility of extended electronic communication throughout the whole molecule. The new chromophores exhibit intense ECD spectra with strong bands in the UV/Vis region well above 400 nm. The anisotropy factor gabs (defined as Δϵ/ϵ) reaches values up to 0.047, which are unusually large for single organic molecules. They also display blue fluorescence, with good quantum yields (Φf∼0.25). The emitted light is circularly polarized to an outstanding extent: in some cases, the luminescence dissymmetry factor glum=2(IL−IR)/(IL+IR) attains values of |0.025|. To the best of our knowledge, such values are among the highest ever reported for non‐aggregated organic fluorophores.