# Hydroquinone/Quinone Cycle for Reductive Photocatalytic Transformations

## TL;DR

Scientists developed a new photocatalytic method using hydroquinone/quinone cycles to efficiently deoxygenate N-heterocyclic compounds under visible light.

## Contribution

The study introduces a novel visible-light-driven reductive photocatalytic system using hydroquinone/quinone cycles with alcohols as hydrogen sources.

## Key findings

- Phenanthrenehydroquinones act as catalytic organic photoreductants under visible light.
- The system efficiently deoxygenates N-heterocyclic N-oxides with lower reduction potentials than the catalyst.
- TD-DFT calculations show H2PQs function as both photoacids and photoreductants.

## Abstract

Phenanthrenehydroquinones
(H2PQs), generated in situ from phenanthrenequinones
under visible light using
alcohols as hydrogen sources, act as catalytic organic photoreductants.
They deoxygenate efficiently diverse N-heterocyclic N-oxides, including substrates having more negative reduction potentials
than the H2PQ excited-state reduction potential (
EH2PQ+·/H2PQ*
= −2.10 V vs SCE), suggesting
hydrogen
bonding assisted electron transfer. TD-DFT calculations indicate H2PQs act as both photoacids and photoreductants. This work
demonstrates the harnessing of the hydroquinone/quinone cycle in visible-light-driven
reductions.