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Issue 4, 2017
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Push–pull pyropheophorbides for nonlinear optical imaging

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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.

Graphical abstract: Push–pull pyropheophorbides for nonlinear optical imaging

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Supplementary files

Article information

24 Oct 2016
20 Dec 2016
First published
20 Dec 2016

Org. Biomol. Chem., 2017,15, 947-956
Article type

Push–pull pyropheophorbides for nonlinear optical imaging

A. Khadria, Y. de Coene, P. Gawel, C. Roche, K. Clays and H. L. Anderson, Org. Biomol. Chem., 2017, 15, 947
DOI: 10.1039/C6OB02319C

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