Laser flash photolysis (LFP) and time-resolved infrared spectroscopy (TRIR) techniques and density function theory (DFT) calculations were used to investigate the electron-transfer chemistry of the triplet excited states of isoquinoline N-oxide (1), benzocinnoline N-oxide (2), and 4-nitroquinoline N-oxide (3). It was found that neither triplet I nor triplet 2 undergoes electron-transfer reactions with typical donors. Rather, they undergo net hydrogen atom transfer (proton-coupled electron transfer) with hydroquinone. Triplet 4-nitroquinoline N-oxide readily undergoes electron-transfer reactions as previously reported, to form the analogous radical anion and hydroradical. The structures of these species were identified by UP and TRIR techniques with the aid of DFT calculations. The oxygen atom on the N-oxide group was found to be the protonation site of the radical anion of 3.