From DPZ to DTQ: Organic Catalysts for Homo- and Heterogeneous Photoredox Processes

Photoredox catalysis has emerged as a powerful strategy for driving redox reactions under exceptionally mild conditions by using light as a clean and controllable energy source. A suitable photocatalyst capable of harvesting light energy and promoting electron-transfer processes is essential for this methodology.¹ Common classes of purely organic photocatalysts include xanthene, acridinium dyes, perylenediimides, and cyanoarenes.²

In 2014, dicyanopyrazine DPZ was introduced as organic photocatalyst, which has been employed in numerous photoredox transformations so far.³ Its mechanism of action and catalytic activity were investigated,⁴ while a recent study revealed that, under blue-light irradiation, DPZ undergoes a Mallory-type photocyclization to dithienoquinoxaline (DTQ).⁵ Its double excited DTQ⁻^· proved to be an exceptionally strong organic reductant capable of chemodivergently reducing nitroaromatics. Hence, utilizing ³DTQ or *DTQ⁻^· and a single blue light source, diethienoquinoxaline can be employed either as a one-electron oxidant or reductant via PET and conPET processes.

DTQ was further immobilized through copolymerization with styrene, generating a polymer-bound photocatalyst (iDTQ). Both powdered material and a flexible monolithic column based on iDTQ were prepared, each retaining the key photophysical and catalytic features of the homogeneous DTQ. iDTQ was successfully applied in both batch and continuous-flow heterogeneous photocatalytic processes.⁶

1 N. A. Romero, D. A. Nicewicz, Chem. Rev. 2016, 116, 10075.

2 H. Wang, C. Zhao, Z. Burešová, F. Bureš, J. Liu, J. Mater. Chem. A 2023, 11, 3753.

3 Z. Burešová, F. Bureš, Chem. Rec. 2025, 25, e202500134.

4 Z. Burešová, H. B. Gobeze, M. Grygarová, O. Pytela, M. Klikar, R. Obertík, R. Cibulka, T. Islam, K. S. Schanze, F. Bureš, J. Catal. 2024, 430, 115348.

5 Z. Burešová, M. Grygarová, E. Prokopová, M. Klikar, O. Pytela, J. Váňa, A. M. M. Fahim, K. Jana, E. Zubova, J. Bartáček, J. Tydlitát, Z. Růžičková, R. Cibulka, K. S. Schanze, F. Bureš, J. Catal. 2025, 445, 116033.

6 M. Klikar, Z. Burešová, J. Bartáček, E. Prokopová, M. Grygarová, J. Svoboda, R. Bulánek, F. Bureš, J. Catal. 2025, 450, 116323.