Tuning and optimizing the intrinsic interactions between phthalocyanine-based PPV oligomers and single-wall carbon nanotubes toward n-type/p-type

In this work we have developed a strategy to immobilize functional groups such as ZnPc onto the surface of SWNT without, however, the needs of covalent functionalization, using substituted PPV-oligomers (1-4) with different electronic character. The complementary use of a series of microscopies and spectroscopies is central, especially to gather a comprehensive picture of the mutual interactions. Importantly, only 1, bearing electron-withdrawing CN substituents, interacts tightly with SWNT affording stable and finely dispersed SWNT suspensions. 2-4, on the other hand, fail to disperse SWNT in THF following our newly developed protocol. A likely rationale is the p-type character of PPV-oligomers 2-4, which imposes repelling forces relative to p-type SWNT, while placing CN groups yields n-type PPV-oligomer 1 and, in turn, strengthens the pi-pi interactions with SWNT. Photoexcitation of SWNT/1 hybrids generates a metastable radical ion pair state, namely oxidized ZnPc and reduced SWNT. Quite remarkable is the ratio of charge separation to charge recombination, namely nearly 3 orders of magnitude, which is encouraging to fabricate photovoltaic cells that are based, for example, on different nanocarbons.