Organic super-reducing photocatalysts generate solvated electrons via two consecutive photon induced processes.

Photocatalysts with extremely strong reducing potential are often thought to operate through a consecutive photoinduced electron transfer (ConPeT) mechanism, where a first photon generates the radical anion of the photocatalyst via electron transfer and a second photon excites the radical anion into a super-reducing agent. Among them, 4CzIPN, (2,4,5,6-tetrakis(9H-carbazol-9-yl) isophthalonitrile) and the analogous 4DPAIPN (2,4,5,6-tetrakis(diphenylamino)isophthalonitrile) are supposed to operate following this principle, but the knowledge of the photophysical properties of the photogenerated radical anions is still very limited. An in-depth spectroscopic and computational study of their radical anions demonstrates that the excited states of 4CzIPN˙- and 4DPAIPN˙- are not behaving as super-reducing agents: they are very short lived (ca. 20 ps), not emissive and not quenched by common organic substrates. Most importantly, longer lived solvated electrons are generated upon excitation of these radical anions in acetonitrile and we propose that it is the solvated electron the species responsible for the exceptional reducing capability of this photocatalytic system.

Stable Meisenheimer Complexes as Powerful Photoreductants Readily Obtained from Aza-Heteroaromatic Compounds.

Excited states of radical anions derived from the photoreduction of stable organic molecules are suggested to serve as potent reductants. However, excited states of these species are too short-lived to allow bimolecular quenching processes. Recently, the singlet excited state of Meisenheimer complexes, which possess a long-lived excited state, was identified as the competent species for the reduction of challenging organic substrates (-2.63 V vs. SCE, saturated calomel electrode). To produce reasonably stable and simply accessible different Meisenheimer complexes, the addition of nBuLi to readily available aromatic heterocycles was investigated, and the photoreactivity of the generated species was studied. In this paper, we present the straightforward preparation of a family of powerful photoreductants (*Eox<-3 V vs. SCE in their excited states, determined by DFT and time-dependent TD-DFT calculations; (DFT, density functional theory) that can induce dehalogenation of electron-rich aryl chlorides and to form C-C bond through radical cyclization. Photophysical analyses and computational studies in combination with experimental mechanistic investigations demonstrate the ability of the adduct to act as a strong electron donor under visible light irradiation.