Conjugated copolymers bearing 2,7-di(thiophen-2-yl)phenanthrene-9,10-dione units and alteration of their emission via functionalization of the ortho-dicarbonyl groups into quinoxaline and phenazine derivatives

Conjugated copolymers were prepared from 2,7-di(thiophen-2-yl)phenanthrene-9,10-dione units with various polycyclic aromatic hydrocarbon moieties, namely, fluorene (PQF1-2), carbazole (PQC), and silafluorene (PQS). Employing mild condensation reaction conditions, PQF1-2 copolymers underwent post-modification of their ortho-dicarbonyl groups into quinoxaline- (PQF3-4) and phenazine- (PQF5-6) derivatives. The copolymers PQF1-6, PQC, and PQS were characterized by different analytical techniques, such as, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), H-1- and C-13 nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), UV-vis absorption, and emission spectroscopy. Post-modification of copolymers PQF1-2 led to interesting changes in the emission properties where the quinoxaline-containing copolymers PQF3-4 portrayed a 20-40 nm hypsochromic shift with a blue emission (similar to 470 nm) whereas copolymers PQF5-6 bearing the more aromatically extended phenazine-units revealed a similar to 55 nm bathochromic shift displaying a green emission (similar to 560 nm).