The Photophysics of Polythiophene Nanoparticles for Biological Applications

Abstract

In this work the photophysics of poly(3-hexylthiophene) nanoparticles (NPs) is investigated in the context of their biological applications. The NPs, made as colloidal suspensions in aqueous buffers, present a distinct absorption band in the low-energy region. On the basis of systematic analysis of absorption and transient absorption (TA) spectra taken under different pH conditions, this band is associated with charge-transfer states generated by the polarization of loosely bound polymer chains and originating from complexes formed with electron-withdrawing species. Importantly, the ground-state depletion of these states upon photoexcitation is active even on microsecond timescales, thus suggesting that they act as precursor states for long-living polarons; this could be beneficial for cellular stimulation. Preliminary transient absorption microscopy results for NPs internalized within the cells reveal the presence of long-living species, further substantiating their relevance in biointerfaces.

Charge-Transfer Intermediates in the Electrochemical Doping Mechanism of Conjugated Polymers

“…This assignment is in agreement with a previous study on the photo-physics of P3HT nanoparticles (NPs) in aqueous buffers. 63 In the case of P3HT NPs dispersed in ultrapure water, the linear absorption showed a spectral component at low energies (~1.8 eV) that is not present or appreciable in thin films of the same material. This component was enhanced in acidic aqueous buffers (pH values from 3 to 11 were tested).…”

“…Because CT states of this nature are mainly non-radiative, the photoluminescence measurements of these NPs were shown to be insensitive to pH variations. 63 Here, in the case of electrochemically addressed ProDOT(OE3)-DMP, the polarization of the excitation could most likely arise from the applied bias and associated ion infiltration into the film.…”

A Polymer Blend Substrate for Skeletal Muscle Cells Alignment and Photostimulation

“…[ 57–61 ] The optical features of the three blends are very similar to that of the neat film suggesting that: a) the fabrication process has a minor effect onto the P3HT photophysics and b) P3HT successfully phase separates from HDPE in the blend. We selected a deposition temperature of 100 °C, in a range in which P3HT is known to phase separate and crystallize [ 62–64 ] prior the HDPE crystallization during the solvent evaporation, [ 40 ] leading to an unperturbed UV‐Vis absorption of the semiconductor.…”

Synthesis, characterization, and biological applications of semiconducting polythiophene‐based nanoparticles

“…Knowing the optical properties of NPs is of great relevance for their application in photobiology and photobiochemistry. Absorption and photoluminescence (PL) spectroscopies allow to study and characterize the absorption and emission of PT‐NPs, the nature of the elementary photoexcitations, and their dynamics in the NPs in different media relevant to biology, as well as to evaluate the stability of the suspension 84 . Furthermore, from the optical properties, it is possible to achieve information on NPs size, shape, concentration, aggregation state, and surface modification.…”