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Relevant academic research and scientific papers

π-Conjugated polymer-Eu3+ complexes: Versatile luminescent molecular probes for temperature sensing

We report π-conjugated polymer-Eu3+ ion complexes as new potential luminescent thermo-sensitive molecular probes. Carboxylic acid functionalized segmented π-conjugated polymers having oligophenylenevinylene (OPV) chromophores in the poly(ethyleneoxide) or polymethylene backbones were custom designed, synthesized and utilized as efficient photosensitizers for Eu3+ ions. These π-conjugated polymer-Eu3+ ion complexes were found to be thermo-sensitive and behaved as reversible 'turn-on' or 'turn-off' luminescent switches in solution and in solid state. Luminescent decay studies revealed that the red-emission from the Eu3+ ion excited state was highly sensitive to temperature which drove the functioning of optical switches. The decay rate constants followed a typical Arrhenius trend over a wide temperature range having similar activation energies. Both the nature as well as length of the segmented polymer chain that tied the OPV optical chromophores in the backbone determine the temperature range of the luminescent on-off process. The emission characteristics of the oligomer-Eu 3+ ion complex were found to be non-thermosensitive which emphasized the need for the segmented π-conjugated polymer ligand structure for the probes based on Eu3+ ion complexes. The present strategy opens up new concept and molecular design principles for π-conjugated polymer-lanthanide ion complexes as potential candidates for temperature sensitive luminescent molecular probes. The Royal Society of Chemistry 2013.

Color-Tunable Amphiphilic Segmented π-Conjugated Polymer Nano-Assemblies and Their Bioimaging in Cancer Cells

We report a unique color tunable amphiphilic segmented π-conjugated polymer design and their π-stack driven diverse self-assembled nanostructures and demonstrate their application as a new classes of aqueous luminescent nanoparticle probes for bioimaging in cervical and breast cancer cells. Oligo-phenylenevinylene (OPV) was employed as rigid luminescent π-core and oligo-ethyleneoxy chains were used as flexible spacers to construct new amphiphilic segmented π-conjugated polymers by Witting-Horner polymerization route. The rigidity of the π-core was varied using tricyclodecanemethyleneoxy, 2-ethylhexyloxy or methoxy pendants and appropriate π-core geometry was optimized to achieve maximum aromatic π-stacking interactions. Solvent-induced chain aggregation of the polymers exhibited a morphological transition from one-dimensional helical nanofibrous to three-dimensional spherical nanoassemblies in good/bad solvent combinations. This morphological transformation was accompanied by the fluorescence color change from blue-to-white-to-yellow. CIE color coordinates exhibited x = 0.25 and y = 0.32 for the white light followed by the collective emission from aggregated and isolated OPV chromophores. Electron and atomic microscopes, steady state photophysical studies, time-resolved fluorescent decay analysis, and dynamic light scattering method enabled us to establish the precise mechanism for the self-assembly of segmented OPV polymers. The polymers produced stable and luminescent aqueous nanoparticles of 200 nm diameter in water. Cytotoxicity studies in cervical and breast cancer cells revealed that these new aqueous luminescent polymer nanoparticles are highly biocompatible and nontoxic to cells up to 60 μg/mL. Cellular uptake studies by confocal microscope further exposed that these nanoparticles were internalized in the cancer cells and they were predominantly accumulated in the nucleus. The present investigation opens up new amphiphilic segmented π-conjugated polymer design for producing diverse supramolecular assemblies and also demonstrates their new application as biocompatible fluorescent nanoprobes for imaging in cancer cells.

Crystallization-driven constitutional changes of dynamic polymers in response to neat/solution conditions

Dynamic polymers (dynamers) based on reversible imine interactions were generated and found to respond to changes in neat/solution environment, thus displaying adaptive behavior through modification of their constitution in order to maximize the stability