Connecting Molecular Conformation to Aggregation in P3HT Using Near Edge X-ray Absorption Fine Structure Spectroscopy

Abstract

Carbon 1s near edge X-ray absorption fine structure (NEXAFS) and UV−vis spectroscopy are used to examine differences between highly aggregated and poorly aggregated forms of the polymer poly(3-hexylthiophene) (P3HT), based on as-cast and annealed regiorandom and regioregular P3HT samples. UV−vis spectra show characteristic signatures of unaggregated P3HT in regiorandom P3HT, and of H-aggregation in regioregular P3HT samples. Distinct spectroscopic differences, including energy shifts, are observed in the NEXAFS spectra of aggregated P3HT relative to the unaggregated forms. These differences are reproduced with transition-potential density functional theory (TP-DFT) calculations which explore aggregation and molecular conformation. Differences in the NEXAFS spectra of P3HT are assigned to thiophene backbone twisting in the unaggregated forms of P3HT, and to various degrees of chain planarization in aggregated forms of P3HT that also correlate to the exciton bandwidth. These results open up the prospect of characterizing conformation and related difficult to assess structural details through NEXAFS spectroscopy and correlative theory and electronic structure analysis.

The optical signatures of molecular-doping induced polarons in poly(3-hexylthiophene-2,5-diyl): individual polymer chainsversusaggregates

“…Yet, to further substantiate our assignment, we measured the optical absorption of BCF : ra-P3HT (1 : 4), where no aggregate formation in solution is expected due to the randomly linked hexyl side chains along the polymer (low percentage of head-to-tail linkage). 31,35 In Fig. S4a (ESI †), the optical absorption spectrum of BCF : ra-P3HT (1 : 4) in solution shows a single P2 absorption feature at 1.5 eV in addition to the P1 absorption feature at 0.6 eV in agreement with our observation in the absorption of individual chains of doped re-P3HT.…”

“…The red shift of the absorption peak is ascribed to more exciton delocalization that accompanies planarization of P3HT chains once formed into ordered aggregates, which results in decreasing its energy. 19,[30][31][32] The absorption fine structure results from the coupling between the electronic and vibrational transitions in crystalline P3HT, as well as the interchain coupling. 1,30 Increasing the temperature of re-P3HT solution in poor solvents increases solubility, and the re-P3HT aggregates transform to individual chains.…”

Predictions of Pattern Formation in Amino Acid Adlayers at the In Vacuo Graphene Interface: Influence of Termination State

“…Regarding experimental characterization, several techniques especially scanning tunneling microscopy (STM), and near edge X‐ray fine absorption structure (NEXAFS) spectroscopy have been used to study patterning formation of amino acid adlayers on various surfaces. In particular, angle‐resolved NEXAFS spectroscopy is well suited for probing the structural orientation of adsorbed organic molecules . However, spectra generated by NEXAFS are complex and typically require integration and iteration with modeling efforts to fully interpret them.…”

Spectral Analysis for Resonant Soft X-Ray Scattering Enables Measurement of Interfacial Width in 3D Organic Nanostructures

“…32 Isolating unique molecular species experimentally is facile for synthetic molecules, and incorporating additional chemistry and orientation through calculations is improving dramatically. 33,34 In this study, three domains were taken into consideration: PS, PMMA, and vacuum. Vacuum is included here to incorporate scattering from surface roughness that is often the source of background that interferes with quantifying scattering signals.…”