Tuning optical properties of poly(3-hexylthiophene) nanoparticles through hydrothermal processing

Abstract

Poly(3-hexylthiophene) (P3HT) nanoparticles (NPs) were prepared by a reprecipitation method. Hydrothermal processing applied external pressure to the pristine P3HT NPs at temperatures ranging from 60 to 150• C. Optical absorption and photoluminescence (PL) spectra for the hydrothermally treated P3HT NPs varied markedly with the processing temperature. With increasing treatment temperature, the absorption peak broadened and the peak position shifted from 510 to 623 nm; moreover, the intensity ratio of the 0-1 to 0-0 emission varied. These changes were caused by interactions between the P3HT main chains and alkyl side groups and conformational modifications induced by the high pressure during the hydrothermal process. The evolution of the optical absorption spectra of the P3HT NPs during the hydrothermal processing was strongly correlated with the variation of PL excitation spectra and with the PL emission spectra of a single NP.

Time-Resolved Raman Spectroscopy of Polaron Pair Formation in Poly(3-hexylthiophene) Aggregates

“…In contrast, Raman spectroscopy is a natural probe for interrogating the structural and morphological characteristics of conjugated polymers and their transient states and has been used extensively to characterize both amorphous and aggregated polymers and polymer-based materials. − Conjugated polymers generally have strong Raman activity along in-phase, intra-ring CC and C–C stretching modes that results from large structural displacements between the ground and excited/charged states . Raman spectroscopy has been demonstrated to be a sensitive probe of intermolecular order, particularly in conjugated materials, with a few groups reporting morphological dependencies in the steady-state Raman spectra of P3HT films. , Significant differences have been observed in the Raman spectra of P3HT films characterized by different degrees of polymer regioregularity, annealing, and doping with electron acceptors (PCBM); lower CC stretching frequencies are consistently observed with films prepared under conditions that promote assembly of ordered polymer domains (e.g., lamellar stacking). ,,− A general explanation for these variations is that higher intra molecular conformational order is obtained with higher inter molecular ordering, resulting in an overall greater delocalization within constituent polymers and corresponding softening of the CC stretch potential. , The sensitivity of this mode to variations in intermolecular order and excited-state or charge (de)­localization implies that time-resolved Raman spectroscopy should provide a valuable probe of the nature of photoinduced transient states in polymer materials.…”

Polymer Nanoparticle Assemblies: A Versatile Route to Functional Mesostructures

“…For nanoparticles prepared by the solvent evaporation method, polymer aggregation can be controlled by the choice of “oil” phase or solvent mixture . Polymer aggregation may also be adjusted postfabrication by hydrothermal annealing of the aqueous nanoparticle dispersion. , …”

Ultrafast Raman Spectroscopy as a Probe of Local Structure and Dynamics in Photoexcited Conjugated Materials

“…In our work, we have applied time-resolved Raman spectroscopy to interrogate how material microstructure impacts the dynamics of charge separation, specifically probing the dynamics of polaron-pair formation in nanoparticle aggregates of P3HT. Like P3HT films prepared for device applications through spin-coating, nanoparticles prepared by polymer reprecipitation (50–200 nm in size) have mixed microstructures that can be recognized readily from their steady-state absorption and Raman spectra. , Additionally, Clafton and Kee demonstrated that nanoparticles and films have qualitatively similar photoinduced dynamics . Given these photophysical similarities with films, suspensions of nanoparticles are convenient samples for multipulse laser experiments (such as time-resolved FSRS) as they have increased optical density compared to films and are highly robust to interactions with laser pulses with high peak powers.…”