Radical Cation π‐Dimers of Conjugated Oligomers as Molecular Wires: An Analysis Based on Nitronyl Nitroxide Spin Labels

Abstract

Nitronyl nitroxide (NN)-substituted conjugated oligomers, which were expected to self-associate in biradical cation states, were designed to analyze the capability of π-dimers as molecular wires. The oligomer moieties were composed of dithienyl-N-methylpyrrole with methoxy substituents at the inner β-position of thiophene rings (DTP-NN ) and its propylenedioxythiophene (ProDOT) inserted derivative (DTP-P-NN ), or two ethylenedioxythiophene (EDOT) and two ProDOT units (E P -NN ). Among them, chemical one-electron oxidation gave biradical cations (DTP-P) -NN and (E P ) -NN that formed π-dimers (DTP-P-NN ) and (E P -NN ) in dichloromethane at low temperatures. ESR studies of (DTP-P-NN ) and (E P -NN ) showed the presence of a relatively strong exchange interaction between two NN radicals through the radical cation π-dimer moieties. DFT calculations supported these experimental results and predicted that exchange interactions between two NN radicals were comparable or stronger than those through covalently linked quaterthiophene. Thus, the conjugated oligomer radical cation π-dimers acted as efficient molecular wires for electronic communication.

Dithienopyrrole Derivatives with Nitronyl Nitroxide Radicals and Their Oxidation to Cationic High‐Spin Molecules

“…The new EPR line appeared during addition of AgSbF 6 along with MeSTh 2 DTP‐Ph‐NN (5 line) but the spectra are not resolved, as demonstrated in Figure S8d. The π‐dimerization of dithienylpyrrole radical cation molecules is known from the literature . Further addition of one more equivalent of the AgSbF 6 , kept at −10 °C for 6 h, five‐line EPR spectra were retained for Ph 2 DTP‐Ph‐NN and MeSTh 2 DTP‐Ph‐NN , the spectra for which are given in Figure S8e,f.…”

“…The p-dimerization of dithienylpyrrole radical cation molecules is known from the literature. [13,22] Further addition of one more equivalent of the AgSbF 6 ,k ept at À10 8Cf or 6h,f ive-line EPR spectra were retained for Ph 2 DTP-Ph-NN and MeSTh 2 DTP-Ph-NN,t he spectra for which are given in FigureS8e,f. These results indicate the dicationf ormation on the DTP core without decompositionoft he NN radical.…”

“…A series of nitronyl nitroxide (NN) substituted triarylamine ( TAA‐NN ), fused arylamine ( FTAA‐NN ), pyrazine ( NNDPP ), thianthrene ( TA‐NN ) phenothiazine ( PTZ‐NN ) and pyrrole‐based molecules and their radical‐cationic forms were reported (Figure S1, Supporting Information (SI)), most of them afforded ground‐state triplet diradicals upon one electron oxidation. In particular, 1‐phenyl NN 4‐substituted‐2,5‐di(thiophen‐2‐yl)‐1 H ‐pyrrole derivatives ( TPT‐Ph‐NN ), and NN‐substituted conjugated oligomers of dithienyl‐ N ‐methylpyrrole with methoxy substituents at the inner β‐position of thiophene rings type of molecules ( DTP‐P‐NN ), were utilized for the synthesis of cationic high‐spin molecules. Therefore our interest focused on the synthesis of stable‐radical species substituted with π‐conjugated electron donor systems and their radical cation formation for high‐spin formation.…”

π‐Dimerization ability of conjugated oligomer dication diradicaloids composed of dithienylpyrrole and benzodithiophene units

“…In the case of 1 2+ and 2 2+ , the VT measurements showed quite similar changes upon lowering the temperature as shown in Figure A,B, indicating that the similar π‐dimerization took place. These results suggested that supramolecular wires based on π‐dimerization between dication diradicaloids in a slipped stack manner were formed at the lower temperatures. Unfortunately, no farther evidence could not be obtained for the formation of supramolecular polymer, partly because the π‐dimerization was observed only at low temperatures in solution phase.…”

Synthesis, Structure, and π-Donor Properties of Tris(ethylenedioxy)benzene and Bis(ethylenedioxy)thiophene

“…5 3,4-Ethylenedioxythiophene 7 and 4,5-ethylenedioxytetrathiafulvalene 8 have been investigated to obtain widely applicable donor molecules, because ethylenedioxy-substituted donors are endowed with enhanced donor ability, stability of radical cations, and moderate solubility in common organic solvents. In the course of our studies on ethylenedioxy-substituted molecules, [9][10][11] we are interested in the synthesis and donor properties of tris(ethylenedioxy)benzene (3) and bis(ethylenedioxy)thiophene (4) (Figure 1). Here, we report an improved synthesis of 3 by using cyclotrimerization of organotin molecules in a one-pot procedure as well as the first synthesis of 4 with insertion of sulfur to 1,4-dilithio-1,3-butadiene unit.…”