N-Doped π-Extended Coumarins: Synthesis and Photophysical Properties of Isoquinoline and Pyrimidine-Fused Coumarins

We present here a novel series of N-doped π-extended coumarins derived from 4-aminocoumarin. Lewis and Bronsted acids mediated synthetic processes have been adopted for their synthesis, enabling the formation of C-C and C-N bonds under transition-metal-free conditions. This previously unexplored process delivers the target π-extended coumarins in good yields and provides access to isoquinoline- and pyrimidine-fused ring systems. Photophysical properties of the resulting compounds were investigated using UV-vis absorption and fluorescence emission spectroscopy. The synthesized compounds exhibit good fluorescence properties, highlighting their potential application for optoelectronic devices and as probes for bioimaging.