Pressure Modulation of Backbone Conformation and IntermolecularDistance of Conjugated Polymers Toward Understanding the Dynamismof π-Figuration of their Conjugated System.

Continuoustuning of the backbone conformation and interchain distanceof a π-conjugated polymer is an essential prerequisite to unveilthe inherent electrical and optical features of organic electronics.To this end, applying pressure in a hydrostatic medium or diamondanvil cell is a facile approach without the need for side-chain syntheticengineering. We report the development of high-pressure, time-resolvedmicrowave conductivity (HP-TRMC) and evaluation of transient photoconductivityin the regioregular poly(3-hexylthiophene) (P3HT) film and its bulkheterojunction blend with methanofullerene (PCBM). X-ray diffractionexperiments under high pressure were performed to detail the pressuredependence of π-stacking and interlamellar distances in P3HTcrystallites and PCBM aggregates. The HP-TRMC results were furthercorrelated with high-pressure Raman spectroscopy and density functionaltheory calculation. The increased HP-TRMC conductivity of P3HT underpressure was found to be relevant to the planarity of the backboneconformation and intramolecular hole mobility. The effects of pressureon the backbone planarity are estimated to be ∼0.3 kJ mol–1based on the compressibility derived from the X-raydiffraction under high pressure, suggesting the high enough energyto cause modulation of the planarity in terms of the Landau-de Gennesfree energy of isolated P3HT chains as 0.23 kJ mol–1. In contrast, the P3HT:PCBM blend showed a simple decrease in photoconductivityirrespective of the identical compressive behavior of P3HT. A mechanisticinsight into the interplay of intra- and intermolecular mobilitiesis a key to tailoring the dynamic π-figuration associated withelectrical properties, which may lead to the use of HP-TRMC for exploringdivergent π-conjugated materials at the desired molecular arrangementand conformation. [ABSTRACT FROM AUTHOR]