Preparation of n-type semiconducting polymer nanoarrays by covalent synthesis followed by crystallization†
In situ covalent synthesis followed by solution crystallization of the n-type semiconducting polymer derived from perylenediimide-bridged silsesquioxanes (PDIB-SSQ) yielded 1D-nanoarrays of 40–100 nm widths and up to 80 μm lengths. Morphologies and dimensions of nanostructures resulting from different base concentrations were characterized by SEM, fluorescence optical microscopy, SAXS, elemental analysis, MALDI-TOF-MS, and absorption and fluorescence spectroscopies. As revealed by SAXS, the nanostructures are composed of crystalline unit cells with cell parameters of d = 24.8 Å and d = 10.3 with multiple π–π stacking distances ranging from 4.71 to 2.57 Å. The ordering in polymer nanoarrays is favoured by the π–π interactions between the cofacially arranged PDI cores, resulting closely packed polymer arrays with the d-spacing ranging from 3.67 Å to 3.24 Å. The spectroscopic traces of nanoarrays in solution resembled that of the monomer except the slightly red shifted features of the emission spectrum associated with π–π stacking of polymer chains in aggregated form. Thin film emission spectra followed the similar spectral pattern with a noticeable shoulder corresponds to cofacial π–π interactions. The excited state lifetimes of aggregated polymer nanoarrays in both solution and solid phase were nearly identical. The electrical characterization of thin films made from polymer nanoarrays shows typical semiconducting behaviour with the electrical conductivity of 0.48 × 10−3 S cm−1. The covalent synthesis followed by solution-based crystallization of PDIB-SSQ reported herein provides a new synthesis path to make ordered-crystalline semiconducting polymer nanoarrays and ultimately a benefit for better understanding of their role in organic electronics.