The synthesis and crystal structure of pH-sensitive fluorescent pyrene-based double aza- and diaza[4]helicenes

Org Biomol Chem. 2022 Mar 30;20(13):2704-2714. doi: 10.1039/d2ob00204c.

Abstract

Novel pyrene-based double aza- and diaza[4]helicenes have been prepared through a five-step synthetic sequence in overall good yields. Commercially available 2,3-dihaloazines (2,3-dibromopyridine, 2,3-dichloropyrazine and 2,3-dichloroquinoxaline) were used as starting materials. The synthesis employs electrophile-induced cyclizations of ortho-alkynyl bihetaryls as the key steps, leading to the formation of a helical skeleton. To discern the effect of merging azine and pyrene moieties within a helical skeleton, the X-ray structures, UV-vis absorption and fluorescence spectra of the helicenes were investigated and compared with those of the parent [4]helicene, aza- and diaza[4]helicenes. It was found that the emission properties of the synthesized helicenes can be modulated as a function of pH. The basicity of pyrene-based double aza[4]helicenes was estimated by the direct fluorimetric titration method; the pKa value was found to be equal to 1.4.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Hydrogen-Ion Concentration
  • Models, Molecular
  • Polycyclic Compounds* / chemistry
  • Pyrenes

Substances

  • Polycyclic Compounds
  • Pyrenes
  • helicenes
  • pyrene