Effect of Spacer Length and Solvent on the Concentration-Driven Aggregation of Cationic Hydrogen-Bonding Donor Polythiophenes

Abstract

Aggregation of cationic isothiouronium polythiophenes with alkoxy-spacers of different lengths at the 3-position of the thiophene ring was studied in solvents of different polarities. Hydrogen-bonding capacity was assessed by steady-state absorption and fluorescence spectroscopy, whereas the aggregation in aqueous solutions was studied by electron paramagnetic resonance spectroscopy, using paramagnetic probes of different polarities. The two polymers displayed similar features in respect to conformation, effect of cosolvents on aggregation, unstructured absorption–fluorescence spectra, Stokes shifts when aggregated, solvatochromic effect, and self-quenching concentration. However, these polymers also showed different specific interactions with water, Stokes shifts in water, effect of the solvent on the extent of dominant state of the S1 level, and also different inner cavities and hydrophobic–hydrophilic surface area in aqueous solution aggregates. Water maximized the difference between the polymers concerning the effect of specific increases in concentration, whereas the presence of 1,4-dioxane generated almost identical effects on both polymers.

Cationic Imidazolium Polythiophenes: Effects of Imidazolium-Methylation on Solution Concentration-Driven Aggregation and Surface Free Energy of Films Processed from Solvents with Different Polarity

“…A previous study from our group using steady-state fluorescence on solutions of cationic isothiouronium polythiophenes also showed aggregation of the polymers around a polymer concentration of 0.2 mM. 34 …”

“…This behavior is opposite to that observed during the concentration-driven aggregation of isothiouronium polythiophenes with spacers of different lengths, under identical experimental conditions to the present work. 34 …”

“… 35 , 36 These spin probes have also been used in our previous EPR study on the concentration-driven aggregation of cationic polythiophenes. 34 …”

Outer‐Membrane Protease (OmpT) Based E. coli Sensing with Anionic Polythiophene and Unlabeled Peptide Substrate

“…[21,22] Av ariety of environmental factors can cause the conjugated backbone to transition from ap lanar to nonplanar conformation including temperature,solvent, an electric field, and dissolved ions. [17,[23][24][25] In the case of PTAA-peptide interactions,t he principal molecular forces influencing the conformational change of the polymer backbone are electrostatic interactions,hydrogen bonding,and to asmaller extent nonpolar interactions. [26][27][28][29] LL37 FRRV carries two arginines Figure 2.…”

Enhancement of charge-assisted hydrogen bond capabilities due to O-alkylation proximity in alkoxy cationic polythiophenes: solution- and solid-state evidence via EPR, AFM and surface free energy

“…[13][14][15][16] Also, their solubility in polar media allows environmentally friendly processing and use in biological environments, 17 while their conjugated backbone provides information about excited states, [17][18][19][20] which change in response to temperature (thermochromism), 21,22 solvent (solvatochromism), 23,24 surfactants (surfactochromism), [25][26][27] irradiation, 8 other chemical species (affinitychromism), 18,28 and/or concentration. 19,29 Such polythiophenes' conformational changes can be detected by absorption, emission, and circular dichroism (CD) spectroscopic methods. 30 Also, as shown in our previous works, 19,31 electron paramagnetic resonance (EPR) spectroscopy allows the tracking of conformational changes of CPTs via spin-probing.…”