Shorter Alkyl Chains Enhance Molecular Diffusion and Electron Transfer Kinetics between Photosensitisers and Catalysts in CO2-Reducing Photocatalytic Liposomes |
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| Authors: | David M Klein Dr Santiago Rodríguez-Jiménez Marlene E Hoefnagel Dr Andrea Pannwitz Amrutha Prabhakaran Dr Maxime A Siegler Prof Tia E Keyes Prof Erwin Reisner Prof Albert M Brouwer Prof Sylvestre Bonnet |
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| Institution: | 1. Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands;2. Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW United Kingdom;3. School of Chemical Sciences and National Centre for Sensor Research, Dublin City University, Dublin 9, Ireland;4. John Hopkins University Department of Chemistry Maryland, 21218 Baltimore, United States of America;5. Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands |
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| Abstract: | Covalent functionalisation with alkyl tails is a common method for supporting molecular catalysts and photosensitisers onto lipid bilayers, but the influence of the alkyl chain length on the photocatalytic performances of the resulting liposomes is not well understood. In this work, we first prepared a series of rhenium-based CO2-reduction catalysts Re(4,4’-(CnH2n+1)2-bpy)(CO)3Cl] ( ReCn ; 4,4’-(CnH2n+1)2-bpy=4,4’-dialkyl-2,2’-bipyridine) and ruthenium-based photosensitisers Ru(bpy)2(4,4’-(CnH2n+1)2-bpy)](PF6)2 ( RuCn ) with different alkyl chain lengths (n=0, 9, 12, 15, 17, and 19). We then prepared a series of PEGylated DPPC liposomes containing RuCn and ReCn , hereafter noted Cn , to perform photocatalytic CO2 reduction in the presence of sodium ascorbate. The photocatalytic performance of the Cn liposomes was found to depend on the alkyl tail length, as the turnover number for CO (TON) was inversely correlated to the alkyl chain length, with a more than fivefold higher CO production (TON=14.5) for the C9 liposomes, compared to C19 (TON=2.8). Based on immobilisation efficiency quantification, diffusion kinetics, and time-resolved spectroscopy, we identified the main reason for this trend: two types of membrane-bound RuCn species can be found in the membrane, either deeply buried in the bilayer and diffusing slowly, or less buried with much faster diffusion kinetics. Our data suggest that the higher photocatalytic performance of the C9 system is due to the higher fraction of the more mobile and less buried molecular species, which leads to enhanced electron transfer kinetics between RuC9 and ReC9 . |
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| Keywords: | artificial photosynthesis CO2 reduction liposomes photocatalysis |
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