Exciton Relaxation in Highly Rigid Conjugated Polymers: Correlating Radiative Dynamics with Structural Heterogeneity and Wavefunction Delocalization

Conjugated polymers are promising materials for solar cells and other electronic applications due to facile charge and electronic energy migration along the conjugated backbone. Torsional defects due to rotation around single bonds on the backbone are known to decrease the effective conjugation length of these materials, limiting their ability to shuttle charge and electronic energy. We investigated the radiative emission dynamics of a recently synthesized rigid conjugated ladder polymer ( LP1 ) and nonrigid control ( CP1 ) with a similar carbazole backbone moiety. LP1 was prepared using a recently reported synthesis under thermodynamic control, leading to a low backbone defect density. We find that the singlet emission lifetime of LP1 is longer than that of any previously reported ladder conjugated polymer, which we attribute to its low defect density. Further, the emission contains a large-amplitude long component with a lifetime that lasts as long as 5 ns. Our results imply that careful control of defects at the synthesis level can lead to processable polymers with large electronic wavefunction delocalization and correspondingly long fluorescence lifetimes. This indicates an avenue to further tune the rapid solid-state energy transport rate along the polymer backbone.