Structural elaboration of dicyanopyrazine: towards push–pull molecules with tailored photoredox activity

Abstract

X-shaped push–pull molecules based on dicyanopyrazine were designed, synthesized and experimentally/theoretically investigated. They proved to be tunable photoredox catalysts in selected chemical transformations.

Recent Advances of Dicyanopyrazine (DPZ) in Photoredox Catalysis

“…In 2012, F. Bureš and co-workers [43,44] presented push-pull molecules based on 5,6-disubstituted pyrazine-2,3-dicarbonitrile (dicyanopyrazine, DPZ) and their nonlinear optical properties were investigated by Jiang group [45,46]. These organic photocatalysts can be readily prepared from available starting materials such as diaminomaleodinitrile (DAMN) in excellent yields (Scheme 1).…”

“…The photochemistry of DPZs reveals that the LUMO is localized in the pyrazine core whereas at the center of the donor groups HOMO is situated at position 5 and 6. [45,46] This polarized system exhibits an effective CT (charge transfer) character (Figure 2) and a short S1 lifetime (<1 ns) that is generated due to their weak fluorescence [47]. Therefore, DPZ photocatalyst exclusively reacts in their T1 state.…”

Selective functionalization of the 1H-imidazo[1,2-b]pyrazole scaffold. A new potential non-classical isostere of indole and a precursor of push–pull dyes

“…43 In addition, some push-pull compounds found application in metal-free photoredoxcatalysis. [44][45] The main donor-acceptor (D-A) interaction in the compounds of type 14 is presumably happening between the malononitrile group, which is widely considered one of the strongest natural electron-withdrawing groups in organic chemistry, [45][46] and the proaromatic electron-donor 2-methylene-2,3-dihydro-1H-imidazole. This group is comparable to the widely explored 1,3-dithiol-2-ylidene (dithiafulvene).…”

Small Heterocyclic D‐π‐D‐π‐A Push‐Pull Molecules with Complex Electron Donors

“…[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Despite their popularity as auxiliary donors, [32] a combination of five-membered heterocyclic and mesomeric donors has been practically realized only on thiophene. [33][34][35] Pyrrole or furan π-linkers with appended alkoxy or amino mesomeric donors are scarce. [36][37][38][39][40] However, such combination can be considered as useful approach towards tuning optoelectronic properties of D-π-A molecules, especially those based on pyrrole and furan.…”

“…On the other hand, recent theoretical and experimental studies showed that proper involvement of thiophene, pyrrole, and furan rings in the chromophore backbone may bring organic materials with advanced properties [14–21,22–31] . Despite their popularity as auxiliary donors, [32] a combination of five‐membered heterocyclic and mesomeric donors has been practically realized only on thiophene [33–35] . Pyrrole or furan π‐linkers with appended alkoxy or amino mesomeric donors are scarce [36–40] .…”