The study of regioselectively introducing functional groups into pyridine derivatives has been considered important from the past. Various photochemical reactions using the special properties of pyridinium salts have been developed. In this dissertation, catalyst-free photochemical cross-coupling reaction between N-amidopyridinium salts and various radicals was described exploiting the photochemical activity of electron donor-acceptor complex. Chapter 1 introduces catalyst- and additive-free C4 selective alkylation, acylation, and carbamoylation of pyridnium derivatives by electron donor-acceptor complex between N-amidopyridinium salts and 1,4-DHPs. Chapter 2 presents a divergent reaction system of the set of N-amidopyridinium salts and sulfinates to enable the sulfonative pyridylation of alkenes under visible-light irradiation and direct C4-sulfonylation of pyridines using base through two distinct pathways.