One-pot Synthesis of Highly Fluorescent Pyrido[1,2-a]indole Derivatives via C-H/N-H Activation: Photophysical Investigations and Application in Cell Imaging

Abstract

We describe a simple strategy for the synthesis of strongly fluorescent pyridoindoles by Pd catalyzed oxidative annulations of internal alkynes with C-3 functionalized indoles via C-H/N-H bond activation in a one-pot tandem process. Mechanistic investigations reveal the preferential activation of N-H indole followed by C-H activation during the cyclization process. Photophysical properties of pyridoindoles exhibited highest fluorescence quantum yield of nearly 80% with emission color varying from blue to green to orange depending on the substructures. Quantum mechanical calculations provide insights into the observed photophysical properties. Strong fluorescence of pyrido[1,2-a]indole derivative has been employed in sub-cellular imaging which unveils its localization in the cell nucleus.