Chemistry Reference
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Figure 11.46 Typical structures of amphiphilic fullerene dendritic derivatives that form
Langmuir-Blodgett films.
Cardullo et al. 1998). These conjugates formed stable monomolecular films
exhibiting reversibility under repeated compression-expansion cycles (Maierhofer
et al. 2000). Although these monolayers could be transferred onto quartz slides,
the transfer ratios were low (0.7), suggesting that the hydrophobic/hydrophilic
balance was not optimal. Nierengarten's group explored a series of dendritic C
60
derivatives displaying both a polar head group to anchor the molecule in the
aqueous phase and hydrophobic poly(benzyl ether) dendrons with terminal alkyl
chains (Felder et al. 2002; Gallani et al. 2002; Hahn et al. 2007) to reduce
fullerene-fullerene interactions (Fig. 11.46b; Nierengarten 2004). Varying the
hydrophilic/hydrophobic balance by increasing the size of the polar head profoundly
improved the stability and transfer properties of the monolayers. The molecular areas
of the amphiphiles decreased with increasing size of the polar head. This behavior
was attributed to a deeper anchoring of the molecules in the aqueous phase, which
forces the hydrophobic dendron branches to collapse upon the fullerene. This confor-
mational change reduces the measured molecular area and inhibits the fullerene-
fullerene interactions that complicate the transfer of the monolayers to solid substrates
(Zhang et al. 2003). Alternatively, the same group demonstrated that dendrons dis-
playing multiple fullerenes at the periphery and a small, focal carboxylic acid were
able to form Langmuir films (Fig. 11.46c; Felder et al. 2000; Hahn et al. 2005).
