Selective Fluorescence Correlation Spectroscopy to Reveal Solvent Effects on P(NDI2OD-T2) Copolymers in Solutions

The performance of semiconducting polymers is strongly influenced by the structural arrangement of the polymer chains. Solvent-induced prestructuring of polymer chains may occur prior to polymer deposition, impacting device performance. We employed fluorescence techniques, including fluorescence correlation spectroscopy (FCS) and single-molecule fluorescence spectroscopy (smFS), to reveal chain conformations of P(NDI2OD-T2) in solutions and characterize aggregate types and sizes as they vary with molecular weight and solvent. The solvent quality for chloronaphthalene and toluene was then quantitatively evaluated by scaling exponents, which were found to be 0.4 for toluene and 0.6 for chloronaphthalene. Small- and wide-angle X-ray scattering were used to probe structural dimensions of the chain and to link structural information to fluorescence properties, such as emission anisotropy, revealing exciton migration and energy transfer within aggregates. The deeper understanding of the relationship between structure and spectral properties may enable the use of structural prearrangement of the polymer chains to optimize device performance.