Twisted-Planar-Twisted expanded porphyrinoid dimer as a rudimentary reaction-based methanol indicator.

Directly linked porphyrin dimers have attracted considerable attention because of their intriguing electronic features. Most emphasis has been placed on either dimers with large dihedral angles between the constituent planar monomeric subunits or those with overall planarity, referred to as "Planar-Twisted-Planar" and "Planar-Planar-Planar", respectively. Herein, we report a "Twisted-Planar-Twisted" framework, the hexaphyrin dimer D that exists in a trans configuration. Treatment of D with MeOH affords two isomeric dimers, MD1 and MD2, both of which incorporate a methoxy moiety and exist in cis orientations with respect to the tethering linkage. The methanol-promoted conversion is accompanied by a readily discernible color change from green to brown and is not induced to an appreciable level by other alcohols. Dimer D thus acts as a rudimentary, albeit highly selective, reaction-based methanol indicator. This work provides a promising approach for constructing reaction-based chemosensors using porphyrinoid dimers of nonplanar subunits with biased reactivity.