Shorter Alkyl Chains Enhance Molecular Diffusion and Electron Transfer Kinetics between Photosensitisers and Catalysts in CO2‐Reducing Photocatalytic Liposomes

Chemistry - A European Journal, vol. 27, pp. 17203–17212

Abstract

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.

Authors 9

1. Santiago Rodríguez‐Jiménez

   University of Cambridge

   Affiliation as printed

   Yusuf Hamied Department of Chemistry University of Cambridge Lensfield Road Cambridge CB2 1EW United Kingdom

   Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW United Kingdom

2. Marlene E. Hoefnagel Aachen

   Leiden University

   Affiliation as printed

   Leiden Institute of Chemistry Leiden University Einsteinweg 55 2333 CC Leiden The Netherlands

   Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands

3. Andrea Pannwitz Aachen

   Leiden University · Universität Ulm

   Affiliation as printed

   Institute of Inorganic Chemistry I Ulm University Albert-Einstein-Allee 11 89081 Ulm Germany

   Leiden Institute of Chemistry Leiden University Einsteinweg 55 2333 CC Leiden The Netherlands

   Institute of Inorganic Chemistry I, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm, Germany

   Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands

4. Amrutha Prabhakaran

   Dublin City University

   Affiliation as printed

   School of Chemical Sciences and National Centre for Sensor Research Dublin City University Dublin 9 Ireland

   School of Chemical Sciences and National Centre for Sensor Research, Dublin City University, Dublin 9, Ireland

5. Maxime A. Siegler

   Johns Hopkins University

   Affiliation as printed

   John Hopkins University Department of Chemistry Maryland 21218 Baltimore United States of America

   John Hopkins University Department of Chemistry Maryland, 21218 Baltimore, United States of America

6. Tia E. Keyes

   Dublin City University

   Affiliation as printed

   School of Chemical Sciences and National Centre for Sensor Research Dublin City University Dublin 9 Ireland

   School of Chemical Sciences and National Centre for Sensor Research, Dublin City University, Dublin 9, Ireland

7. Erwin Reisner

   University of Cambridge

   Affiliation as printed

   Yusuf Hamied Department of Chemistry University of Cambridge Lensfield Road Cambridge CB2 1EW United Kingdom

   Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW United Kingdom

8. Albert Manfred Brouwer

   University of Amsterdam

   Affiliation as printed

   Van 't Hoff Institute for Molecular Sciences University of Amsterdam Science Park 904 1098 XH Amsterdam The Netherlands

   Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands

9. Sylvestre A. Bonnet corresponding Aachen

   Leiden University

   Affiliation as printed

   Leiden Institute of Chemistry Leiden University Einsteinweg 55 2333 CC Leiden The Netherlands

   Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands