Fluorinated Arylethynyl Substituents in Zn(II) Complexes of Azadipyrromethene Guide Self-Assembly in Crystals
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Updated: Nov 3, 2026

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
Published on: March 24, 2018
David A Raufman1, Neha Jadhav1, Shashika A Arachchige1
1Department of Chemistry, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio44106, United States.
Abstract:
Zn(II) complexes of 2,8-arylethynyl 1,3,7,9-tetraphenyl azadipyrromethenes are promising molecular semiconductors with strong visible-NIR absorption and a nonplanar distorted tetrahedral geometry around the Zn(II) center, but their charge transport properties are limited by the orientation and strength of intermolecular π-π stacking interactions. To optimize their intermolecular π-π stacking interactions, we explored substitution of the pyrrolic phenylethynyl groups in Zn(L1)2 at the phenyl meta positions with either fluorines (Zn(L1-m-2F)2) or trifluoromethyls (Zn(L1-m-2CF3)2). Fluorination had minimal effects on optical properties and slightly deepened frontier orbital energy levels. On the other hand, fluorination strongly affected the complexes' molecular packing: while Zn(L1-m-2F)2 had the same C2/c space group as Zn(L1)2, the -CF3 groups in Zn(L1-m-2CF3)2 promoted a higher ordered space group of Fddd. Further, in Zn(L1)2 and Zn(L1-m-2F)2, the phenylethynyl groups stack with the core phenyls of neighboring molecules, whereas in Zn(L1-m-2CF3)2, the bis(trifluoromethyl)-substituted phenylethynyl groups of neighboring molecules stack with each other with a shorter π-π stacking distance than in the other two molecules. Computations revealed that fluorination decreases the internal reorganization energy for electron transfer and increases overlap integrals for charge transfer. Fluorination is thus a promising strategy to tune molecular packing and parameters relevant to charge transport.
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