One Well-Placed Methyl Group Increases the Solubility of Phenoxy Boronsubphthalocyanine Two Orders of Magnitude

Boronsubphthalocyanine (BsubPc) derivatives
are materials
that have recently seen an increase in attention, particularily for
application as colorants and functional materials in organic electronic
devices. However, the solubilities of most BsubPc derivatives
are too low to utilize solution-based processing techniques. Where
there are derivatives that are soluble, they rely on the addition
of large alkyl chains for solubilization the result of which is an
increase in the molecular weight and a decrease of the specific absorptivity
of the BsubPc. In this paper we disclose the identity
of two mass-efficient, highly soluble BsubPc derivatives:
3-methylphenoxy-BsubPc and 3,4-dimethylphenoxy-BsubPc. We compare their solubilities and crystal packing
structures to previously known BsubPc derivatives. We
put forward a symmetry-based argument for the reason for their surprisingly
high solubility wherein we treat the molecules as two separate fragments:
the phenoxy group and the BsubPc group. The symmetry-based
argument suggests that by ignoring the BsubPc fragment
common to each derivative a better estimate of the relative solubilities
can be estimated through previously established empirical formulas.