Despite continuous research interests in conjugated polymers (CPs) as a promising alternative to traditional inorganic semiconductors, the morphological and associated electronic properties in CPs still remain ambiguous due to their inherently heterogeneous structure. Flexible chain-linked oligomers, as a simplified model of CPs, can not only offer an insight into the interactions between chromophores in CPs but also provide a potential substitute for CPs to realize predictable and controlled nanostructures. Herein, single molecule spectroscopy and theoretical simulations were employed to study a model polymer composed of bis(2-ethylhexyl)-p-phenylene vinylene (BEH-PPV) oligomers joined with flexible linkers. It was found in our previous study that the folding order of the polymer increases with oligomer conjugation length; where PPV trimers adopt a disordered, isotropic configuration compared with the more anisotropic PPV pentamers and heptamers. To probe if the folding of even these trimer polymers could be controlled with enhanced monomer interactions, polymers with hydrogen-bonding side chains were synthesized. Two motifs were used with predicted structures: side chain stacking and backbone stacking. The otherwise isotropic structures of the PPV trimers demonstrated higher folding order induced by the hydrogen-bonding on side-chains as probed by their single molecule fluorescence excitation polarization. The influence of this chromophore ordering, as a result of different hydrogen bonding, on photophysics was also demonstrated.
[1] M. C. Traub, K. H. DuBay, S. E. Ingle, X. Zhu, K. N. Plunkett, D. R. Reichman, D. A. Vanden Bout, J. Phys. Chem Lett., 4, 2520-2524 (2013).