Researchers develop highly fluorescent helical quinolizinium salts via rhodium-catalyzed synthesis

A research team has successfully synthesized a new class of helical quinolizinium salts exhibiting exceptionally strong fluorescence in the orange-to-red light region (606–682 nm).

The work, published in the journal Chemical Communications, combines cutting-edge rhodium-catalyzed [2+2+2] cyclotrimerization and C–H activation strategies to efficiently build complex helical molecular architectures with remarkable optical properties.

In the first stage, appropriately substituted diynes were subjected to Rh-catalyzed cyclotrimerization with trimethylsilylethyne, yielding 1-arylisoquinolines in isolated yields of up to 61%. These intermediates then underwent C–H activation and annulation with various aryl and alkyl disubstituted alkynes, forming [7]-helical quinolizinium salts in yields reaching 93%.

The team also explored enantioselective C–H activation, achieving up to 62% enantiomeric excess (ee), marking a promising step toward chiral control in helical aromatic systems. In addition, boron and platinum complexes derived from the 1-arylisoquinolines were successfully prepared, further expanding the material’s photophysical diversity.

All synthesized compounds display strong fluorescence quantum yields (ΦF = 28–99%), making them attractive candidates for applications in organic light-emitting diodes (OLEDs), sensors, and photonic materials.