Employing Click Chemistry to Expand the Scope of the Metal-Free Donor-Acceptor-Type Photocatalyst 4CzIPN

The design of a versatile alkyne-bearing derivative of the donor-acceptor fluorophore 2,4,5,6-tetrakis(9H-carbazol-9-yl) isophthalonitrile (4CzIPN) suitable for further targeted modifications by copper-catalysed Azide Alkyne Cycloaddition (CuAAC) is reported. The newly synthesised photoredox catalyst notably exhibits analogously unique photoelectronic and steric features as the well-established carbazolyl dicyanobenzene motif and performs equally in a C-C-Coupling model reaction. Furthermore, the variability of this donor-acceptor system was demonstrated by the generation of a library of fourteen photoredox catalysts with electron-withdrawing and -donating groups as well as residues with high steric demands in one simple and selective CuAAC reaction. The modified catalysts feature a broad scope of reducing and oxidising powers in their excited states (span of reducing powers over more than 1 V) and were also successfully applied in the photoredox and nickel-catalysed decarboxylative cross coupling model reaction. This work represents a method to overcome the limitations in the flexibility of metal-free donor-acceptor fluorophores required for the targeted application in organic synthesis and paves the way for the design of customised catalysts with multiple functionalities.

Automated summary

A versatile alkyne-bearing derivative of a donor-acceptor fluorophore was designed for targeted modifications. The newly synthesised photoredox catalyst exhibited unique photoelectronic and steric features, and showed effectiveness in a C-C-Coupling model reaction. This work represents a method to overcome the limitations in the flexibility of metal-free donor-acceptor fluorophores and paves the way for the design of customised catalysts with multiple functionalities.