Copper‐Based Photosensitisers in Water Reduction: A More Efficient In Situ Formed System and Improved Mechanistic Understanding

Abstract

The reduction of water has been achieved through a non-noble-metal-based homogeneous catalyst system that is formed in situ. Optimisation of the ligand quantities increased catalyst turnover numbers compared to preformed complexes. Mechanistic studies confirm a heteroleptic Cu complex as the active photosensitiser (PS) and an in situ formed Fe-phosphido dimer complex as the water reduction catalyst. The in situ method has been used to screen a range of ligands for the active PS, which has led to the identification a number of structural features important to longevity and performance.

The effects of introducing sterically demanding aryl substituents in [Cu(N^N)(P^P)]+complexes

“…15,16 Related complexes find application in oxygen sensing, 17 CO 2 reduction, 18 and water reduction. 19,20 The N^N ligand in [Cu(N^N)(POP)] + and [Cu(N^N)(xantphos)] + is usually a 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen) derivative, and the introduction of simple substituents into the 6-and 6'-positions of bpy or 2-and 9-positions of phen modulates the emission properties of the complexes. 4,7,8 We recently demonstrated the remarkable performance of [Cu(N^N)(POP)][PF 6 ] and [Cu(N^N)(xantphos)][PF 6 ] (N^N = 6-methyl-2,2'-bipyridine, 6-ethyl-2,2'-bipyridine or 6,6'-dimethyl-2,2'-bipyridine) in LECs.…”

Designing Highly Efficient CuI Photosensitizers for Photocatalytic H2 Evolution from Water

“…[5] Many noble-metal-free complexes have been reported as photosensitizers for HER as well, buto nly few of them showedalevel of catalytic activity for HER comparable with their noble-metal-basedc ounterparts. [7][8][9] We recently reported high-performance photosensitizers consistingo fa n[ Ir III (C^N) 2 (bpy-R)] + scaffold,i nw hich C^N is am onoanionic cyclometalating ligand and bpy-R is a4 ,4'-disubstituted 2,2'-bipyridyl ligand.B ye mploying tetraphenylsilane (TPS) as ab ulky Rm oiety,s tate-of-the-artT ONs of 17 000 could be achieved with this [Ir III (C^N) 2 (bpy-R)] + photosensitizer. [7][8][9] We recently reported high-performance photosensitizers consistingo fa n[ Ir III (C^N) 2 (bpy-R)] + scaffold,i nw hich C^N is am onoanionic cyclometalating ligand and bpy-R is a4 ,4'-disubstituted 2,2'-bipyridyl ligand.B ye mploying tetraphenylsilane (TPS) as ab ulky Rm oiety,s tate-of-the-artT ONs of 17 000 could be achieved with this [Ir III (C^N) 2 (bpy-R)] + photosensitizer.…”

“…It is notable that the tert-amine-containing complexes,C u-TPAPhen and Cu-DMAPhen, showedp eculiar photophysical properties totally different from the other Cu I complexes.T hese two complexes showedo ne order of magnitude higher molar absorptivities (e)i nt he visible region and significantly higherP LQYs compared to the other complexes (see Figure 1a nd Ta ble 1). [7][8][9][12][13][14] In contrast, the HOMO of Cu-TPAPheni sl ocalizedi nt he amine moieties, and the electronic transition can be assigned to intra-ligand charge-transfer (ILCT). Although such long PL lifetimes of [Cu I (P^P)(N^N)] + complexes have been attributed to the thermally activated delayedf luorescence( TADF), [11] the significantly different absorption and emission behaviors of tert- amine-containing complexes compared to those of other Cu I complexes should be rationalized.…”

“…To evaluatet he intrinsic efficacy of the [Cu I (P^P)(N^N)] + photosensitizer in addition to excluding complicated side effects of other components, [9,13] ah ighly efficient Scheme1.Chemical structures of photosensitizers. To evaluatet he intrinsic efficacy of the [Cu I (P^P)(N^N)] + photosensitizer in addition to excluding complicated side effects of other components, [9,13] ah ighly efficient Scheme1.Chemical structures of photosensitizers.…”

Structure‐Activated Copper Photosensitisers for Photocatalytic Water Reduction

“…Previously, we reported the successful application of a series of heteroleptic copper(I) complexes with the general formula [Cu(N^N)(P^P)]PF 6 as photosensitisers . In our recent mechanistic studies, we demonstrated that the dominant species observed in solution is the heteroleptic complex [Cu(P^P)(N^N)]PF 6 . Indeed, this was found to be the active PS species, rather than the homoleptic species [Cu(N^N) 2 ] + (or [Cu(P^P) 2 ] + ), which was only formed initially in very low quantities and its growth over time correlated to the H 2 production rate decay.…”