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Colloquium – Newton Barbosa Neto – Photon Manipulation of Molecules
April 27, 2022 @ 3:30 pm - 5:00 pm
Speaker: Newton M. Barbosa Neto (Institute of Natural Sciences, Federal University of Pará, Brasil)
Title: Photoinduced manipulation of conjugated polymers and molecules via sequential two-photon absorption
Solution processing of conjugated polymers into ordered self-assembled precursors has attracted great interest in the past years owing to the ability to manipulate their structural and physical properties. Regioregular poly(3-hexylthiophene) (P3HT) has become the benchmark polymer in this scenario, where ordered lamellar structures significantly improve carrier mobility of the thin films due to increased crystallinity, extended intrachain conjugation, and ordered interchain π-stacking. Here, a new photoinduced approach that utilizes sequential two-photon absorption, also known as excited-state absorption (ESA), to generate highly ordered P3HT lamellar precursors in solution, in a controlled way, is presented. Strong intra- and interchain interactions in the solution precursors allow for the permanent formation of localized and delocalized polarons that are stable for months. Spin-coated thin films are found to preserve, in part, the morphological and physical properties of the aggregated P3HT solution precursors with a high degree of crystallinity and short π-stack interchain distances. Beyond conjugated polymers, the use of ESA to controlled promote the protonation of porphyrin molecules is also presented. Porphyrins are highly conjugated macrocyclic molecules with great potential to be employed in molecular electronics and photonics mainly due to their unique electronic properties that can be tunned through structural manipulation. The porphyrin structure dependence for ESA-induced protonation is proved and the mechanism behind such process is presented. The case studies presented here point to the use of ESA as a versatile, precise, reproducible, and non-destructible tool to structurally manipulate conjugated species in precursor solutions.