Catalytic C-C/C-H Bond Activation Relay for Synthesis of Fluorescent Naphthoquinolizinium Salts

Herein, we report the design and synthesis of a series of novel cationic nitrogen-embedded polyaromatic hydrocarbons with a planar geometry. The synthetic pathway is based on catalytic C-C/C-H bond activation relay that enabled preparation of regioselectively 5,6,10,11-tetrasubstituted naphtho[2,1,8-ija]quinolizinium salts bearing various types of substituents. Single-crystal X-ray analyses of selected compounds confirmed planarity of the quinolizinium core. Most of the prepared compounds exhibited strong fluorescence (f(s) up to >99 %) ranging from 420-600 nm depending on the substitution pattern. According to DFT calculations LUMO is always distributed over the quinolizinium framework regardless of the attached substituents, whereas delocalization of HOMO is related to the substitution pattern. Electrochemical measurements show irreversible reduction of all compounds, which is supported by the calculated location of LUMO orbitals.

Automated summary

Here, the design and synthesis of a series of novel cationic nitrogen-embedded polyaromatic hydrocarbons with a planar geometry are reported. The synthesis pathway is based on catalytic C-C/C-H bond activation relay, enabling the preparation of selectively-regioselective 5,6,10,11-tetrasubstituted naphtho[2,1,8-ija]quinolizinium salts with various substituents. Single-crystal X-ray analysis confirmed the planarity of the quinolizinium core. Most of the synthesized compounds exhibited strong fluorescence, ranging from 420-600 nm, depending on the substitution pattern. DFT calculations revealed that the LUMO is always distributed over the quinolizinium framework while the delocalization of HOMO is related to the substitution pattern. Electrochemical measurements showed irreversible reduction of all compounds, which is consistent with the calculated location of LUMO orbitals.