Synthesis and Properties of Benzodithiophene-Based Donor-Acceptor Metallo-Supramolecular Polymers

Two new conjugated donor-acceptor (D-A) supramolecular building blocks, which contain benzo[1,2-b:4,5-b']dithiophene (BDT) electron-donating cores modified with alkoxy (BDT-OR) or thiophene (BDT-Th) groups and electron-accepting 2,2':6',2"-terpyridine moieties, were synthesized via Pd-catalyzed Stille coupling. Under the introduction of transition metal ion Ru2+, the novel metallo-supramolecular polymers PBDT-OR and PBDT-Th were obtained by self-assembly polymerization of the monomeric building blocks BDT-OR and BDT-Th, respectively. The resulting polymers exhibitbroad absorption band from 300 to 600 nm. The embedding of the transition metal ions Ru2+ into the backbones of the supramolecular polymers increases the electron-withdrawing capacity of the terpyridine moieties. Consequently, the absorption bands of both PBDT-OR and PBDT-Th exhibit red-shift at the longer wavelength compared with the corresponding monomeric building blocks, 622 nm for PBDT-OR and 625 nm for PBDT-Th, which results from intramolecular charge transfer (ICT). The LUMO energy levels of PBDT-OR and PBDT-Th are similar, −3.44 and −3.43 eV, respectively, while their HOMO energy levels are different, −5.25 and 5.17 eV, respectively, due to distinct electron-donating abilities of the BDT cores modified with alkoxy and thiophene groups. PBDT-OR and PBDT-Th show reduced electrochemical energy gaps, 1.81 and 1.74 eV, respectively. Meanwhile, the resulting polymers PBDT-OR and PBDT-Th are thermally stable under 300 and 389 °C, respectively. Open image in new window