Effects of acceptors on the electronic and optoelectronic properties of fluorene-based donor-acceptor-donor copolymers

In this study, four fluorene-based conjugated copolymers were synthesized to explore the acceptor effects on the electronic and optoelectronic properties. The studied polymers were poly{[2,7-(9,9-dihexylfluorene)]-alt-[2,2':5,2 ''-terthiophene]} (PFTT) and its derivatives of poly{ [2,7(9,9'-dihexylfluorene)]-alt-[2,3-dimethyl-5,7-dithien-2-yl-quinoxaline]} (PFDDTO), poly{[2,7-(9,9'-dihexylfluorene)]-alt-[4,7-dithien-2-yl-2,1,3-benzothiadiazole]} (PFDTBT), and poly{[2,7-(9,9'dihexylfluorene)]-alt-[2,3-dimethyl-5,7-dithien-2-yl-thieno[3,4-b]pyrazine]} (PFDDTTP) with the acceptors of quinoxaline (Q), 2,1,3-benzothiadiazole (BT), and thieno[3,4-b]pyrazine (TP), respectively. The order of the band gap was PFDTTP < PFDTBT < PFDDTO < PFTT, which was on the reverse trend of emission maximum and field-effect transistor (FET) mobility. The strong acceptor strength of the TP moiety and coplanar backbone in PFDTTP resulted in the highest intramolecular charge transfer (ICT) among the four polymers. The FET mobility of PFDTTP could be varied by two orders of magnitude through the solvent quality. The present study suggested the importance of the acceptor structure on the electronic and optoelectronic properties of semiconducting polymers.