Acetylene Derivatives of Cationic Diazaoxatriangulenes and Diaza [4]Helicenes - Access to Red Emitters and Planar Chiral Stereochemical Traits.
Pavol OndrisekMargaux ElieMarion PupierIgnacio Funes-ArdoizAmalia I Poblador BahamondeCéline BesnardJérôme LacourPublished in: Chemistry (Weinheim an der Bergstrasse, Germany) (2022)
Cationic triangulenes, and related helicenes, constitute a rich class of dyes and fluorophores, usually absorbing and emitting light at low energy, in the orange to red domains. Recently, to broaden the scope of applications, regioselective late-stage functionalizations on these core moieties have been developed. For instance, with the introduction of electron-donating groups (EDGs), important bathochromic shifts are observed pushing absorptions towards or in the near-infrared (NIR) spectral domain while emissive properties disappear essentially completely. Herein, to upset this drawback, acetylene derivatives of cationic diazaoxa triangulenes (DAOTA) and [4]helicenes are prepared (16 examples). Contrary to other EDG-functionalized derivatives, C≡C- functionalized products remain broadly fluorescent, with red-shifted absorptions (Δλ abs up to 25 nm) and emissions (Δλ em up to 73 nm, Φ PL up to 51 %). Quite interestingly, a general dynamic stereoisomerism phenomenon is evidenced for the compounds derived from achiral DAOTA cores. At low temperature in 1 H NMR spectroscopy (218 K), N-CH 2 protons become diastereotopic with chemical shifts differences (Δδ) as high as +1.64 ppm. The signal coalescence occurs around 273 K with a barrier of ∼12 kcal mol -1 . This phenomenon is due to planar chiral conformations (S p and R p configurations), induced by the geometry of the alkyl (n-propyl) side-chains next to the acetylenic substituents. Ion pairing studies with Δ-TRISPHAT anion not only confirm the occurrence of the chiral conformations but evidence a moderate but definite asymmetric induction from the chiral anion onto the cations. Finally, DFT calculations offer a valuable insight on the geometries, the corresponding stereodynamics and also on the very large difference in NMR for some of the diastereotopic protons.
Keyphrases
- ionic liquid
- quantum dots
- room temperature
- light emitting
- photodynamic therapy
- capillary electrophoresis
- density functional theory
- magnetic resonance
- structure activity relationship
- high resolution
- risk assessment
- fluorescent probe
- magnetic resonance imaging
- molecular dynamics
- living cells
- gene expression
- mass spectrometry
- genome wide
- computed tomography
- molecular dynamics simulations
- fluorescence imaging
- drug delivery
- drug release
- heavy metals
- tandem mass spectrometry