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.