p-Conjugated polymers hold a great promise in photovoltaic applications. Their properties are generally believed to follow a linear 1/n trend, where n is the number of monomer units. The present study shows that the origin of 1/n dependence and the reasons for its breakdown can be related to the mechanism of hole stabilization on the example of various poly-p-phenylene (PP) cation radicals. A multi-state parabolic model (MPM), developed and validated in this study, revealed the critical role of end-capping substituents in determining the hole position within the molecule. Thus, a symmetric, bell-shaped hole in unsubstituted PPs becomes either slightly skewed and shifted towards an end of the molecule in iso-alkyl-capped PPs, or highly deformed and concentrated on a terminal unit in PPs with strongly electron-donating iso-alkoxy capping groups. Besides the end-capping groups, hole distribution and optoelectronic properties of PP cation radicals can be modulated by introducing a linker between adjacent p-phenylene units, as well as by change of the polymer topology. The obtained insights along with the readily-applicable and flexible multi-state parabolic model can guide studies of complex donor-spacer-acceptor systems and doped molecular wires to aid the design of the next generation materials for long-range charge transport and photovoltaic applications.

Multi-state parabolic model: New insights into relationships between structure and optoelectronic properties of p-conjugated polymer cation radicals

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.