title: How mobile are dye adsorbates and acetonitrile molecules on the surface of TiO2nanoparticles? A quasi-elastic neutron scattering study.
abstract: Motions of molecules adsorbed to surfaces may control the rate of charge transport within monolayers in systems such as dye sensitized solar cells. We used quasi-elastic neutron scattering (QENS) to evaluate the possible dynamics of two small dye moieties, isonicotinic acid (INA) and bis-isonicotinic acid (BINA), attached to TiO2nanoparticles via carboxylate groups. The scattering data indicate that moieties are immobile and do not rotate around the anchoring groups on timescales between around 10 ps and a few ns (corresponding to the instrumental range). This gives an upper limit for the rate at which conformational fluctuations can assist charge transport between anchored molecules. Our observations suggest that if the conformation of larger dye molecules varies with time, it does so on longer timescales and/or in parts of the molecule which are not directly connected to the anchoring group. The QENS measurements also indicate that several layers of acetonitrile solvent molecules are immobilized at the interface with the TiO2on the measurement time scale, in reasonable agreement with recent classical molecular dynamics results.
authors.affiliation: Department of Physcis, Imperial College London, London, SW72AZ, United Kingdom.|Centre for Plastics Electronics, Imperial College London, SW72AZ, United Kingdom.
authors.forename: Valerie
authors.initials: V
authors.lastname: Vaissier
authors.affiliation: ISIS Pulsed neutron and Muon Source, Rutherford Appleton Laboratory, Didcot, OX11 0QX, United Kingdom.
authors.forename: Victoria Garcia
authors.initials: VG
authors.lastname: Sakai
authors.affiliation: Department of Chemistry, Imperial College London, London, SW72AZ, United Kingdom.
authors.forename: Xiaoe
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Chemical Engineering, Imperial College London, London, SW72AZ, United Kingdom.|Centre for Plastics Electronics, Imperial College London, SW72AZ, United Kingdom.
authors.forename: João T
authors.initials: JT
authors.lastname: Cabral
authors.affiliation: Department of Physcis, Imperial College London, London, SW72AZ, United Kingdom.|Centre for Plastics Electronics, Imperial College London, SW72AZ, United Kingdom.
authors.forename: Jenny
authors.initials: J
authors.lastname: Nelson
authors.affiliation: Department of Physcis, Imperial College London, London, SW72AZ, United Kingdom.|Centre for Plastics Electronics, Imperial College London, SW72AZ, United Kingdom.
authors.forename: Piers R F
authors.initials: PR
authors.lastname: Barnes