Verdazyls as Possible Building Blocks for Multifunctional Molecular Materials: A case Study on 1,5-Diphenyl-3-(p-iodophenyl)-verdazyl Focusing on Magnetism, Electron Transfer and the Applicability of the Sonogashira-Hagihara Reaction

Abstract

This work explores the use of Kuhn verdazyl radicals as building blocks in multifunctional molecular materials in an exemplary study, focusing on the magnetic and the electron transfer (ET) characteristics, but also addressing the question whether chemical modification by cross-coupling is possible. The ET in solution is studied spectroscopically whereas solid state measurements afford information about the magnetic susceptibility or the conductivity of the given samples. The observed results are rationalized based on the chemical structures of the molecules, which have been obtained by X-ray crystallography. The crystallographically observed molecular structures as well as the interpretation based on the spectroscopic and physical measurements are backed up by DFT calculations. The measurements indicate that only weak, antiferromagnetic coupling is observed in Kuhn verdazyls owed to the low tendency to form face-to-face stacks, but also that steric reasons alone are not sufficient to explain this behavior. Furthermore, it is also demonstrated that ET reactions proceed rapidly in verdazyls/verdazylium redox couples and that Kuhn verdazyls are suited as donor molecules in ET reactions.

Influence of the Increasing Number of Organic Radicals on the Structural, Magnetic, and Electrochemical Properties of the Copper(II)–Dioxothiadiazole Family of Complexes

“…Even though the library of organic radicals is enormous, 3 , 20 , 37 − 40 only a few classes dominate the field of molecular magnetism, and these are verdazyls, 41 , 42 nitronyl nitroxides, 43 , 44 semiquinones, 45 , 46 and TTF, TCNE, and TCNQ derivatives. 47 − 52 The popularity of these four groups is dictated by their stability, chemical tunability, coordination abilities promoting strong magnetic interactions, and electrochemical properties providing electron transfer and enabling various types of switching properties.…”

“…5 Among many different functionalities of radical-based magnetic compounds, the following seem to be the most popular: electronic conductivity, 12−14 long-range magnetic ordering, 15−19 valence tautomerism, 6,20−22 photomagnetism, 20,23−28 luminescence, 29−32 and single molecule and single chain magnet behavior (SMM and SCM). 3,33−36 Even though the library of organic radicals is enormous, 3,20,37−40 only a few classes dominate the field of molecular magnetism, and these are verdazyls, 41,42 nitronyl nitroxides, 43,44 semiquinones, 45,46 and TTF, TCNE, and TCNQ derivatives. 47−52 The popularity of these four groups is dictated by their stability, chemical tunability, coordination abilities promoting strong magnetic interactions, and electro- chemical properties providing electron transfer and enabling various types of switching properties.…”