Small internal reorganization energy is desirable for high-performance optoelectronic materials, as it facilitates both charge separation and charge transport. However, only a handful of n-type electron accepting materials are known to have small reorganization energies. Here, DFT calculations were performed to predict the reorganization energy of azadipyrromethene-based dyes and their complexes. All compounds studied were most stable in their anionic state and had high electron affinity, indicating their potential as n-type material. The homoleptic zinc(II) complexes had significantly lower reorganization energies than either the free ligands or the BF2(+) chelates. The low reorganization energies of the zinc(II) complexes are explained by the large and rigid π conjugated system that extends across the two azadipyrromethene ligands via interligand π-π interactions. This work suggests that Zn(II) complexation is a novel strategy for obtaining materials that combine low internal reorganization energy with high electron affinity for the development of novel n-type optoelectronic materials.
Azadipyrromethene (ADP) ligands substituted with thienylethynyl substituents either at the distal phenyl groups H(CD1) or the proximal phenyl groups H(CD2) were synthesized and characterized. The thienyl groups have a hexyl group at the third position to improve solubility in organic solvents and prevent homocoupling of the ethynylthiophene reactants. To further tune the opto-electronic properties, the substituted ADPs were coordinated with BF 2 + and Zn II . Absorption spectroscopy shows that the thienylethynyl substitu-
Azadipyrromethene (ADP)‐based complexes have gained interest due to their strong absorption in the visible to near‐IR region and high electron affinity. Attempts to increase their electron accepting properties by electron withdrawing group substitutions have been limited. We previously found that substitution with fluorine at the p‐distal phenyls or at the p‐pyrrolic‐phenylethynyls of ADP do not shift reduction potentials and thus have no effect on electron affinity. This could be because fluorine also acts as pi‐donor, thus, a pi‐acceptor substituent may have a greater impact on the energy levels. To test this hypothesis, we synthesized three new ADP‐based complexes with nitrile substitutions. Cyclic voltammetry shows that the nitrile substitutions indeed anodically shifts the reduction potentials, leading to increased electron affinity. The shift was ≈ 0.3 V for the p‐distal phenyl substitution and 0.16V for the p‐phenylethynyl substitution. Nitrile substitution was also found to improve electron accepting ability and electron mobility in diodes, as compared to the un‐substituted analogues.
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