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Thin films of poly(arylene ethynylene) conjugated polymers, including low-energy-gap donor–acceptor polymers, can be prepared via stepwise polymerization utilizing surface-confined Sonogashira cross-coupling. This robust and efficient polymerization protocol yields conjugated polymers with a precise molecular structure and with nanometer-level control of the organization and the uniform alignment of the macromolecular chains in the densely packed film. In addition to high stability and predictable and well-defined molecular organization and morphology, the surface-confined conjugated polymer chains experience significant interchain electronic interactions, resulting in dominating intermolecular π-electron delocalization which is primarily responsible for the electronic and spectroscopic properties of polymer films. The fluorescent films demonstrate remarkable performance in chemosensing applications, showing a turn-off fluorescent response on the sub-ppt (part per trillion) level of nitroaromatic explosives in water. This unique sensitivity is likely related to the enhanced exciton mobility in the uniformly aligned and structurally monodisperse polymer films. 

This work establishes a correlation between the selectivity of hydrogen-bonding interactions and the functionality of micelle-containing layer-by-layer (LbL) assemblies. Specifically, we explore LbL films formed by assembly of poly(methacrylic acid) (PMAA) and upper critical solution temperature block copolymer micelles (UCSTMs) composed of poly(acrylamide- co -acrylonitrile) P(AAm- co -AN) cores and polyvinylpyrrolidone (PVP) coronae. UCSTMs had a hydrated diameter of ∼380 nm with a transition temperature between 45 and 50 °C, regardless of solution pH. Importantly, micelles were able to hydrogen-bond with PMAA, with the critical interaction pH being temperature dependent. To better understand the thermodynamic nature of these interactions, in depth studies using isothermal titration calorimetry (ITC) were conducted. ITC reveals opposite signs of enthalpies for binding of PMAA with micellar coronae vs. with the cores. Moreover, ITC indicates that pH directs the interactions of PMAA with micelles, selectively enabling binding with the micellar corona at pH 4 or with both the corona and the core at pH 3. We then explore UCSTM/PMAA LbL assemblies and show that the two distinct modes of PMAA interaction with the micelles ( i.e. whether or not PMAA binds with the core) had significant effects on the film composition, structure, and functionality. Consistent with PMAA hydrogen bonding with the P(AAm- co -AN) micellar cores, a significantly higher fraction of PMAA was found within the films assembled at pH 3 compared to pH 4 by both spectroscopic ellipsometry and neutron reflectometry. Selective interaction of PMAA with PVP coronae of the assembled micelles, achieved by the emergence of partial ionization of PMAA at pH 4 was critical for preserving film functionality demonstrated as temperature-controlled swelling and release of a model small molecule, pyrene. The work done here can be applied to a multitude of assembled polymer systems in order to predict suppression/retention of their stimuli-responsive behavior.