Ion-Pairing-Modulated Diradical Properties in Partially Conjugated Negatively Charged π-Electronic Systems
Hiroto Kobayashi1, Takashi Kubo2, Shinya Sugiura1
1Department of Applied Chemistry, College of Life Sciences, Ritsumeikan University, Kusatsu, 525-8577, Japan.
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A quinonoidal dipyrrolyldiketone catecholate-boron complex, with two pyrrole-quinonemethide moieties bridged by a six-membered cross-conjugated unit, was synthesized to modulate the diradical character of the dianion formed upon deprotonation. The dianionic species exhibited near-infrared absorption and electron spin resonance (ESR) signals, confirming the diradical properties. Variable-temperature (VT) ESR spectra suggest the thermal excitation from the ground-state singlet diradical to the triplet diradical, providing singlet-triplet energy gaps modulated by coexisting cations and bridging boron moieties.
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