Synthesis, photophysical properties, and computational studies of benzothiadiazole and/or phenothiazine based donor/acceptor π-conjugated copolymers

The benzothiadiazole/hexylthiophene, benzothiadiazole/hexylthiophene/N–hexylphenothiazine, benzothiadiazole/N-hexylphenothiazine alternating π-conjugated copolymers were synthesized via Pd-catalyzed cross-coupling reaction. The main structural differences among the three copolymers are the type of donor moiety (hexylthiophene and/or hexylphenothiazine). The polymer structures and photophysical properties were characterized by 1H NMR, 13C NMR, GPC, TGA, DSC, UV–vis absorption spectroscopy, PL spectroscopy, CV, and XRD measurement. The work is aimed at exploring the structural factors that could control the photophysical properties of copolymers in order to help in the rational design of polymers having specific physical properties used in optoelectronic devices. XRD of all copolymers showed a d-spacing range of 4.04 ~ 3.91 Å, reflecting the π-π stacking and some degree of crystallinity in their structure. Their PL spectra showed red and near infrared light, which nominates them as potential red and near infrared light-emitting materials for PLEDs. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were employed in an attempt to supplement and explained the experimental measurement. The preliminary photovoltaic prediction of the studied copolymers was also reported.