Regioisomers of Organic Semiconducting Dumbbell‐Shaped Molecules: Synthesis and Structure‐Properties Relationship

Abstract

Two new dumbbell-shaped molecules based on two solubilizing and structuring triazatruxene (TAT) units linked by a central chromophore were synthesized and studied. The central chromophore was an electro-deficient fluorene-malononitrile (FM) unit, that can be functionalized symmetrically on two different positions, giving rise to two positional isomers, called TAT-pFM and TAT-mFM, when the TATs are connected to the 2,7-and 3,6-positions, respectively. The two isomers exhibited different electronic conjugation pathways that drastically affect their absorption properties and energy levels. Moreover, while TAT-pFM was organized in a stable 3D mesomorphic structure from room-temperature to the melting point, TAT-mFM remained crystalline and decomposed before melting. Finally, despite a lower hole mobility, the TAT-mFM exhibited the highest Power Conversion Efficiency (PCE) of about 2 % in organic solar cells. This higher PCE was attributed essentially to the pronounced internal charge transfer band contribution to the charge photogeneration observed in TAT-mFM solar cells.

Synthesis of 1,6/7‐(NO2)2‐Perylenediimide and 1,6/7‐(NH2)2‐Perylenediimide as Regioisomerically Pure Materials**

“…Nevertheless, similarly to the case of the spectroscopic studies, the electrochemical investigations presented here highlight the differences of electronic behaviour and properties of each distinct regioisomer. It is worth emphasizing that the optoelectronic properties of chromophores, including semiconductors, are tuned on account of their regioisomerism [50–54] . The different optoelectronic properties of the regioisomerically pure dyes are summarized in Table 1, which demonstrates and renders the separation of these regioisomers of key importance for their implementation in advanced optoelectronic devices.…”

“…It is worth emphasizing that the optoelectronic properties of chromophores, including semiconductors, are tuned on account of their regioisomerism. [50][51][52][53][54] The different optoelectronic properties of the regioisomerically pure dyes are summarized in Table 1, which demonstrates and renders the separation of Chemistry-A European Journal these regioisomers of key importance for their implementation in advanced optoelectronic devices.…”