Photocatalytic H2 production using a hybrid assembly of an [FeFe]-hydrogenase model and CdSe quantum dot linked through a thiolato-functionalized cyclodextrin

It is a great challenge to develop iron-based highly-efficient and durable catalytic systems for the hydrogen evolution reaction (HER) by understanding and learning from [FeFe]-hydrogenases. Here we report photocatalytic H-2 production by a hybrid assembly of a sulfonate-functionalized [FeFe]-hydrogenase mimic (1) and CdSe quantum dot (QD), which is denoted as 1/beta-CD-6-S-CdSe (beta-CD-6-SH = 6-mercapto-beta-cyclodextrin). In this assembly, thiolato-functionalized beta-CD acts not only as a stabilizing reagent of CdSe QDs but also as a host compound for the diiron catalyst, so as to confine CdSe QDs to the space near the site of diiron catalyst. In addition, another two reference systems comprising MAA-CdSe QDs (HMAA = mercaptoacetic acid) and 1 in the presence and absence of beta-CD, denoted as 1/beta-CD/MAA-CdSe and 1/MAA-CdSe, were studied for photocatalytic H-2 evolution. The influences of beta-CD and the stabilizing reagent beta-CD-6-S- on the stability of diiron catalyst, the fluorescence lifetime of CdSe QDs, the apparent electron transfer rate, and the photocatalytic H-2-evolving efficiency were explored by comparative studies of the three hybrid systems. The 1/beta-CD-6-SCdSe system displayed a faster apparent rate for electron transfer from CdSe QDs to the diiron catalyst compared to that observed for MAA-CdSe-based systems. The total TON for visible-light driven H-2 evolution by the 1/beta-CD-6-S-CdSe QDs in water at pH 4.5 is about 2370, corresponding to a TOF of 150 h(-1) in the initial 10 h of illumination, which is 2.7- and 6.6-fold more than the amount of H-2 produced from the reference systems 1/beta-CD/MAA-CdSe and 1/MAA-CdSe. Additionally, 1/beta-CD-6-S-CdSe gave 2.4-5.1 fold enhancement in the apparent quantum yield and significantly improved the stability of the system for photocatalytic H-2 evolution.