Attaining solution processability together with elevated SWNT concentrations and high degree of individualization presents one of the greatest challenges in nanotubes Photovoltaics. While covalent functionalization can ultimately prevent phase separation, the interruption in the extended π-conjugation of SWNTs dramatically reduces both carrier mobility and uniformity of pristine SWNTs. Consequently, substantial effort has been directed towards non-covalent functionalization methods. Since these surfactants are difficult, if not impossible, to be removed from SWNT bulk heterojunctions, considerable engineering has gone to outfit them with exciton dissociation capabilities as well. Conjugated polymers are a classic example for such surfactants, whose multi-dentate attachment inhibits SWNT/surfactant dissociation. On the other hand, SWNT dispersion involving C60 and its derivatives were proven more challenging due to their single, as opposed to multi-dentate attraction, with SWNTs. Engineering multi-dentate capabilities to C60 acceptors can, in principle, address this challenge; so long that purity and band-uniformity are equally tackled. To this effect, the supramolecular organizations of flavin mononucleotide (FMN) around single walled carbon nanotubes (SWNTs) was shown to provide effective nanotube dispersions and the ability to impart selective enrichment of sem-SWNTs by recognizing the underlying nanotube helical pattern. In this work, we report the synthesis of a C60-functionalized flavin (FC60), where a PCBM moiety is attached to an isoalloxazine ring via a terminal C-12 aliphatic spacer. Unlike physical mixtures of FC12 and PCBM, their covalent coupling induces an effective photoluminescence (PL) quenching for FC60 in dilute solutions via a bended conformation that allows the C60 moiety to form charge-transfer (CT) interactions with the isoalloxazine ring. The equally strong CT interaction with the graphene sidewalls affords only a few percent FC60 incorporation within FC12-dispersed nanotubes. The incorporation of as much as 1% FC60, causes effective SWNT photo-induced CT quenching as indicated by both steady state and transient spectroscopic technique. In addition, the minimal broadening in SWNT ESii transitions by the incorporation of few percent of FC60 suggests that such a system could ultimately yield a variety of optoelectronic and electro-optic devices with spectrally sharp response in the visible and NIR.

Photoluminescence quenching of single-walled carbon nanotubes through C60: Functionalized flavin helices

251st National Meeting (2016)

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