π-Conjugated polyphenylene gels with charge transfer structures assisted by TCNQ

The reaction of π-conjugated poly(p-phenylene)s (PPPs) consisting of 2- or 3-amino-1,4-phenylene (NH2Ph) and 2,5-dioctyloxy-1,4-phenylene (OctPh) or 9,9-dihexylfluorene-2,7-diyl (HexFlu) rings [polymer-1: (NH2Ph-OctPh)n and polymer-2: (NH2Ph-HexFlu)n] with 7,7,8,8-tetracyanoquinodimethane (TCNQ) yielded gel-1 and gel-2. These gels were form through a charge transfer (CT) between the NH2 group and TCNQ, causing the gels to be linked by a TCNQ dianion. ESR measurements suggest that radical species generated by CT in the gels are delocalized in the π-conjugated polymer backbone. UV-vis measurements revealed that CT between the NH2 group and TCNQ was essential for gel formation. When a dimethyl sulfoxide (DMSO)/TCNQ solution was added to a chloroform solution of the polymers, the absorption corresponding to CT bands increased with an increasing amount of TCNQ. Photoluminescence (PL) measurements suggested that TCNQ served as a quencher for fluorescent polymer-1 and polymer-2. Quenching behavior was investigated by Stern-Volmer analysis.