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Influence of Hofmeister I– on Tuning Optoelectronic Properties of Ampholytic Polythiophene by Varying pH and Conjugating with RNA
journal contribution
posted on 2017-10-13, 00:00 authored by Radhakanta Ghosh, Dhruba P. Chatterjee, Sujoy Das, Titas K. Mukhopadhyay, Ayan Datta, Arun K. NandiA significant
tuning of optoelectronic properties of polythiophene
(PT) chains due to Hofmeister iodide (I–) ion is
demonstrated in ampholytic polythiophene [polythiophene-g-poly{(N,N,N-trimethylamino
iodide)ethyl methacrylate-co-methacrylic acid}, APT]
at different pHs. In acidic medium, the absorption and emission signals
of PT chromophore exhibit appreciable blue shift in the presence of
I– as counteranion only. The cooperative effect
of undissociated -COOH and quaternary ammonium groups immobilize I– near the apolar PT chain causing threading of grafted
chains and hence twisting of the backbone attributing to the blue
shift. As medium pH is increased, dethreading of the PT backbone occurs
due to ionization of -COOH group, releasing quencher iodide ions from
the vicinity of the PT chains resulting in a red shift in absorption
and a sharp hike in fluorescence intensity (390 times) for an increase
of excitons lifetime. With an increase of pH, morphology changes from
a multivesicular aggregate with vacuoles to smaller size vesicles
and finally to nanofibrillar network structure. Dethreading is also
found when APT interacts with RNA showing a significant hike of fluorescence
(22 times) for displacing iodide ions forming a nanofibrillar network
morphology. Threading and dethreading also affect the resistance,
capacitance, and Warburg impedance values of APT. Molecular dynamics
simulation of a model APT chain in a water box supports the threading
at lower pH where the iodide ions pose nearer to the PT chain than
that at higher pH causing dethreading. So the influence of Hofmeister
I– ion is established for tuning the optoelectronic
properties of a novel PT based polyampholyte by changing pH or by
conjugating with RNA.
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Keywords
quaternary ammonium groups immobilizeHofmeisterWarburg impedance valuesoptoelectronic propertiespolythiophenequencher iodide ionsCOOHshiftRNApHTuning Optoelectronic Propertiesnanofibrillar network structuremodel APT chainPT chromophore exhibitdethreadingMolecular dynamics simulationapolar PT chaindisplacing iodide ionsnanofibrillar network morphology