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.

Photophysical, thermal, and DFT studies on a tetraaryl-azadipyrromethene ligand and its zinc(II) complex

“…The −1 and −7 hydroxymethyl-substituted azadipyrromethene ligand ( H1 ) and corresponding zinc(II) complex ( H1-Zn ) were synthesized over a sequence of steps as shown in the Scheme . The ligand was synthesized in three steps [ 8 – 10 ]. The aldol condensation of the corresponding 4-(hydroxymethyl)benzaldehyde with acetophenone resulted in the formation of chalcone, which is a β -unsaturated carbonyl compound, and then the addition of nucleophilic nitromethane to it by Michael addition reaction followed by a condensation reaction with an ammonium source in refluxing n -BuOH afforded the corresponding azadipyrromethene.…”

“…The presence of π-interactions is also expected to increase the rigidity of the complex [ 7 ]. When the ligand and complex were compared with their analogs in the literature [ 6 , 8 – 10 ], there were similarities in absorption wavelengths and molar absorbances. In this respect, it can be stated that the hydroxymethyl groups in the −1 and −7 positions of the indacene structure practically do not alter the photophysical behaviors in terms of absorption profiles.…”