Modulation of conductance using light-induced morphological change of a layered π-structure

Abstract

Photoinduced aggregation–disaggregation behaviour of a tetraphenylethene (TPE)-based molecule has been reversibly achieved upon photoisomerization of a photochromic dihydropyrene (DHP)-conjugated TPE derivative. The DHP–TPE conjugate forms planar stacks because of its aggregation. The highly conjugated π-system in the DHP form displays a high conductance. The conductance results from π-conjugation of the stacked aromatic system. Upon photoisomerization, the planar aromatic dihydropyrene (DHP) units convert to non-planar cyclophanediene (CPD) units. This DHP→CPD photoisomerization results in the disruption of the π-conjugation as well as the morphology of the well-stacked π-system. Thus, the conductance of the photoisomerized system in the CPD form drops drastically. Upon exposure to UV light or heating, the photoisomerized sample in the CPD-form reverts to the DHP form. This reversal of the CPD to the DHP re-establishes the aggregation through π-stacking and the restoration of the high conductance of the sample. This work demonstrates a light-tunable switching of bulk conductance through the aggregation–disaggregation and morphological modulation of an organic system.