title: Fluorescent molecular rotors based on the BODIPY motif: effect of remote substituents.
abstract: The ability of an unconstrained boron dipyrromethene dye to report on changes in local viscosity is improved by appending a single aryl ring at the lower rim of the dipyrrin core. Recovering the symmetry by attaching an identical aryl ring on the opposite side of the lower rim greatly diminishes the sensory activity, as does blocking rotation of the meso-aryl group. On the basis of viscosity- and temperature-dependence studies, together with quantum chemical calculations, it is proposed that a single aryl ring at the 3-position extends the molecular surface area that undergoes structural distortion during internal rotation. The substitution pattern at the lower rim also affects the harmonic frequencies at the bottom of the potential well and at the top of the barrier. These effects can be correlated with the separation of the H1,H7 hydrogen atoms.
authors.affiliation: Molecular Photonics Laboratory, School of Chemistry, Bedson Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK. anthony.harriman@ncl.ac.uk.
authors.forename: Effat
authors.initials: E
authors.lastname: Bahaidarah
authors.forename: Anthony
authors.initials: A
authors.lastname: Harriman
authors.forename: Patrycja
authors.initials: P
authors.lastname: Stachelek
authors.forename: Sandra
authors.initials: S
authors.lastname: Rihn
authors.forename: Elodie
authors.initials: E
authors.lastname: Heyer
authors.forename: Raymond
authors.initials: R
authors.lastname: Ziessel