Reduction of dipyrido-[3,2-a:2′,3′-c]-phenazine (dppz) by photolysis in ethanol solution

Abstract

Photolysis of dipyrido-[3,2-a:2',3'-c]-phenazine (dppz) (1) in ethanol solution leads to the formation of 9,14-dihydrodipyridophenazine (2), which has been characterised by detailed NMR analysis, UV/VIS absorption spectroscopy, and theoretical calculations which reveal that its red colour is due to a low-lying intramolecular charge transfer state.

Photoinduced Ligand Transformation in a Ruthenium Polypyridophenazine Complex

“…Illumination of 3 in acetonitrile under aerobic conditions does not lead to any observable oxidation of the central tatpp ligand structure. Even prolonged irradiation over 72 h did not result in the formation of detectable amounts of the corresponding oxidation product [(tbbpy) 2 Ru(tatpq)Ru(tbbpy) 2 ](PF 6 ) 4 . It should be noted that peroxy disulfate oxidation of 3 and related bpy and phen analogues quantitatively yields the quinone (tatpq) products.…”

“…[10,11] To the best of our knowledge, this is the first time that such a product has been isolated in good yield and the structure was confirmed by X-ray crystallography. [3,4]phenazine-11,16-quinone, dpbqz. [8] We postulate that the oxidation process involves singlet oxygen which is created by triplet sensitisation from the excited ruthenium 3 MLCT state.…”

“…[3] For example the redox activity of dipyridophenazine has recently been employed for photochemical reduction of the central pyrazine moiety to dihydropyrazine in various alcohols. [4] The capacity of the dinuclear ruthenium complexes of 9,11,20,22-tetraazatetrapyrido[3,2-a:2Ј,3Ј-c:3ЈЈ,2ЈЈ-l:2ЈЈЈ,3ЈЈЈ-n]pentacene (tatpp) and its related quinone 9,11,20,22-tetraazatetrapyrido[3,2-a:2Ј,3Ј-c:3ЈЈ,2ЈЈ-l:2ЈЈЈ,3ЈЈЈ-n]pentacene-10,21-quinone (tatpq) derivative to reversibly store up to four electrons using directional photoelectron transfer has been reported. [5] The investigation of related ligand systems, tetrapyridophenazine, has recently let to a report on the light driven catalytic production of hydrogen using a heterodinuclear ruthenium palladium complex.…”

Unraveling the Light‐Activated Reaction Mechanism in a Catalytically Competent Key Intermediate of a Multifunctional Molecular Catalyst for Artificial Photosynthesis

“…[24] Theinvestigations towards the effect of blue-light irradiation of the catalytic reaction mixture containing BNA + clearly showed that once the doubly reduced Ru-(tpphz)RhCp* state is formed, photoexcitation impedes the catalytic hydrogenation of BNA + to BNAH. To the best of our knowledge,wepresented, for the first time,the results of in-situ early-time photodynamics of an isolated, molecular photocatalyst in its active electronic configuration.…”

An Experimental and Computational Study on Intramolecular Charge Transfer: A Tetrathiafulvalene‐Fused Dipyridophenazine Molecule

“…[11] In addition, a recent report by Kelly et al highlights its specific photochemical behavior. [12] The herein reported novel organic compound TTF-dppz (1), which emerges from the annulation of sulfur-and nitrogen-containing polycycles, allows a thorough experimental and theoretical study of photoinduced charge transfer (CT) in a single D-A molecule. In fact, this transfer occurs between spatially separated electron-rich and electron-deficient fragments within the extended polycyclic system.…”