Biomimetic zinc chlorin-poly(4-vinylpyridine) assemblies: Doping level dependent emission-absorption regimes

Ville Pale, Taru Nikkonen, Jaana Vapaavuori, Mauri Kostiainen, Jari Kavakka, Jorma Selin, Ilkka Tittonen, Juho Helaja

    Research output: Contribution to journalArticleScientificpeer-review

    25 Citations (Scopus)

    Abstract

    To develop biomimetic dye-polymers for photonics, two different types of Zn chlorin-poly(4-vinylpyridine) (P4VP) assemblies were prepared by varying Zn pyro-pheophorbide a methylester (ZnPPME) and Zn 31-OH-pyro- pheophorbide a methylester (Zn-31-OH-PPME) doping levels. 1H NMR spectroscopy and diffusion ordered NMR spectroscopy (DOSY) studies revealed that a coordinative interaction between Zn chlorin and P4VP was predominant in solution (d5-nitrobenzene). Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) characterization of bulk samples of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) doped with variable amounts of Zn chlorin showed that the pigment doping transformed the native cylindrical block copolymer nanostructures to lamellar morphologies. The result indicates that the pyridine moiety-Zn chlorin coordination is stronger than the aggregation tendency between the pigment molecules even in the solid state. UV-Vis absorption spectroscopy studies of a Zn chlorin-P4VP thin film showed characteristic monomeric chlorin spectra, while steady-state fluorescence spectroscopy displayed quenching of fluorescence and time-resolved studies indicated shortening of fluorescence lifetimes with an increasing chlorin doping level. Notably, time-resolved fluorescence spectroscopy revealed that the lifetime decay changed from monoexponential to biexponential above 0.5 wt% (ca. 0.001 equiv.) loadings. The Förster analysis implies that excitonic chlorin-chlorin interactions are observed in the thin films when the distance between the pigment molecules is approximately 50 Å. The Zn chlorin-P4VP solid films emit strongly up to 1 wt% (ca. 0.002 equiv.) doping level above which the chlorin-chlorin interactions start to linearly dominate with an increase of doping level, while with 10 wt% (ca. 0.02 equiv.) loading less than 10% of fluorescence remains. Doping levels up to 300 wt% (0.5 equiv.) can be used in absorbing materials without the formation of chlorin aggregates. These defined optical response regions pave the way for photonic materials based on biopigment assemblies.

    Original languageEnglish
    Pages (from-to)2166-2173
    Number of pages8
    JournalJournal of Materials Chemistry C
    Volume1
    Issue number11
    DOIs
    Publication statusPublished - 21 Mar 2013
    Publication typeA1 Journal article-refereed

    ASJC Scopus subject areas

    • General Chemistry
    • Materials Chemistry

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