Synthesis and Properties of Azadipyrromethene-Based Complexes with Nitrile Substitution

Abstract

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.