Open AccessThe Design of Radical Stacks: Nitronyl‐Nitroxide‐Substituted Heteropentacenes
Author(s) -
Tretyakov Evgeny,
Keerthi Ashok,
Baumgarten Martin,
Veber Sergey,
Fedin Matvey,
Gorbunov Dmitry,
Shundrina Inna,
Gritsan Nina
Publication year - 2017
Publication title -
chemistryopen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 29
ISSN - 2191-1363
DOI - 10.1002/open.201700110
Subject(s) - nitroxide mediated radical polymerization , crystallography , diradical , thiophene , chemistry , alkyl , intramolecular force , crystal structure , polymerization , stereochemistry , materials science , polymer , radical polymerization , organic chemistry , physics , nuclear physics , singlet state , excited state
The first alkyl chain‐anchored heteropentacene, dithieno[2,3‐ d ;2′,3′‐ d ′]benzo‐[1,2‐ b ;3,4‐ b ′]dithiophene (DT m BDT), mono‐ or disubstituted with a nitronyl nitroxide group has been prepared through a cross‐coupling synthetic procedure of the corresponding dibromo‐derivative (Br 2 ‐DT m BDT) with a nitronyl nitroxide‐2‐ide gold(I) complex. The synthesized nitroxides possess high kinetic stability, which allowed us to investigate their structure and thermal, optical, electrochemical, and magnetic properties. Single‐crystal X‐ray diffraction of both mono‐ and diradicals revealed that the nitronyl nitroxide group lies almost in the same plane as the nearest side thiophene ring. Such arrangement favors formation of edge‐to‐edge dimers, which then form close π‐stacks surrounded by interdigitating alkyl chains. Before melting, these nitronyl nitroxide radical substituted molecules undergo at least two different phase transitions (PTs): for the monoradical, PTs are reversible, accompanied by hysteresis, and occur near 13 and 83 °C; the diradical upon heating shows a reversible PT with hysteresis in the temperature range 2–11 °C and an irreversible PT near 135 °C. PTs of this type are absent in Br 2 ‐DT m BDT. Therefore, the step‐by‐step substitution of bromine atoms by nitronyl nitroxide groups changes the structural organization of DT m BDT and induces the emergence of PTs. This knowledge may facilitate crystal engineering of π‐stacked paramagnets and related molecular spin devices.