title: Push-pull pyropheophorbides for nonlinear optical imaging.
abstract: Pyropheophorbide-a methyl ester (PPa-OMe) has been modified by attaching electron-donor and -acceptor groups to alter its linear and nonlinear optical properties. Regioselective bromination of the terminal vinyl position and Suzuki coupling were used to attach a 4-(N,N-diethylaminophenyl) electron-donor group. The electron-acceptor dicyanomethylene was attached at the cyclic ketone position through a Knoevenagel condensation. Four different derivatives of PPa-OMe, containing either electron-donor or electron-acceptor groups, or both, were converted to hydrophilic bis-TEG amides to generate a series of amphiphilic dyes. The absorption and emission properties of all the dyes were compared to a previously reported push-pull type porphyrin-based dye and a commercial push-pull styryl dye, FM4-64. Electrochemical measurements reveal that the electron donor group causes a greater decrease in HOMO-LUMO gap than the electron-acceptor. TD-DFT calculations on optimized geometries (DFT) of all four dyes show that the HOMO is mostly localized on the donor, 4-(N,N-diethylaminophenyl), while the LUMO is distributed around the chlorin ring and the electron-acceptor. Hyper-Rayleigh scattering experiments show that the first-order hyperpolarizabilities of the dyes increase on attaching either electron-donor or -acceptor groups, having the highest value when both the donor and acceptor groups are attached. Two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) images of the bis-TEG amide attached dyes in lipid monolayer-coated droplets of water-in-oil reveal that the TPEF and SHG involve transition dipole moments in different orientations.
authors.affiliation: Department of Chemistry, Oxford University, Chemistry Research Laboratory, Mansfield Road, Oxford OX1 3TA, UK. harry.anderson@chem.ox.ac.uk.
authors.forename: Anjul
authors.initials: A
authors.lastname: Khadria
authors.affiliation: Department of Chemistry, University of Leuven, Celestijnenlaan 200 D, 3001 Leuven, Belgium. Koen.Clays@fys.kuleuven.be.
authors.forename: Yovan
authors.initials: Y
authors.lastname: de Coene
authors.affiliation: Department of Chemistry, Oxford University, Chemistry Research Laboratory, Mansfield Road, Oxford OX1 3TA, UK. harry.anderson@chem.ox.ac.uk.
authors.forename: Przemyslaw
authors.initials: P
authors.lastname: Gawel
authors.affiliation: Department of Chemistry, Oxford University, Chemistry Research Laboratory, Mansfield Road, Oxford OX1 3TA, UK. harry.anderson@chem.ox.ac.uk.
authors.forename: Cécile
authors.initials: C
authors.lastname: Roche
authors.affiliation: Department of Chemistry, University of Leuven, Celestijnenlaan 200 D, 3001 Leuven, Belgium. Koen.Clays@fys.kuleuven.be.
authors.forename: Koen
authors.initials: K
authors.lastname: Clays
authors.affiliation: Department of Chemistry, Oxford University, Chemistry Research Laboratory, Mansfield Road, Oxford OX1 3TA, UK. harry.anderson@chem.ox.ac.uk.
authors.forename: Harry L
authors.identifier: http://orcid.org/0000-0002-1801-8132
authors.initials: HL
authors.lastname: Anderson