Bistable Charge-Transfer Complex Formation of Redox-Active Organic Molecules Based on Intermolecular HOMO−LUMO Interaction Controlled by the Redox Reactions

Abstract

Bistable complex formation systems consisting of biphenylene (BP) and redox-active organic molecules such as chloranil (CL) and TCNE have been experimentally and theoretically investigated, based on an intermolecular interaction which characteristically occurs in the electrogenerated dianions forming a π-π type chargetransfer (CT) complex. Initially, we examined the CT complex formation of CL 2and TCNE 2with hydrocarbons (BP, hexamethylbenzene (HMB), and anthracene (AN)). Spectroelectrochemistry evidently gave the intermolecular CT spectra in the CL 2--BP and TCNE 2--BP systems at 500 and 550 nm, respectively. The CT interaction between the dianions and BP was measured as the positive shift of the second reduction potential with increasing concentrations of BP. This behavior allowed the formation constants to be estimated as 33.9 and 20.3 dm 3 mol -1 at 25 °C for the CL 2and TCNE 2complexes in CH 2 Cl 2 containing 0.5 mol dm -3 tetrabutylammonium perchlorate, respectively. Temperature dependence of the formation constants yielded the formation energy as 31.6 and 39.8 kJ mol -1 for the CL 2--BP and TCNE 2--BP systems, respectively. However, the CT spectra and the marked behavior in the voltammograms were not observed in the dianion systems involving HMB and AN. The RHF/6-31G(d) calculations reveal that the CL 2--BP and TCNE 2--BP complex formations are due to molecular recognition based on the favorable intermolecular HOMO-LUMO interaction of the dianions with BP, and the geometries of the dianion complexes differ from those of the neutral complexes. This background led to the development of redox-mediated bistable complex formation systems characterized by the geometrical alteration and the chromatic change. The interconversion of the bistable complex formation in the systems is modulated through redox control of the intermolecular HOMO-LUMO interaction, with trichromic change arising from the neutral complex formation, the anion radical generation, and the dianion complex formation.

Acid/base and hydrogen bonding effects on the proton-coupled electron transfer of quinones and hydroquinones in acetonitrile: Mechanistic investigation by voltammetry, 1H NMR and computation

“…These studies clearly indicated that hydrogen bonding on its own can significantly alter the electrochemistry of quinoid compounds even though actual PT does not occur. Recently this was confirmed for several quinoid and phenolic systems that display inter-and intra-molecular hydrogen bonding [15,[17][18][19]24,[37][38][39][40][41][42]. Unlike the techniques used in such studies, 1 H NMR can provide direct evidence of hydrogen bonding, because molecular association in solution decreases the diffusion coefficient (D) of the species involved and the spatial location of hydrogen bonding within the molecules can be traced from the chemical shift in titration experiments [43].…”

“…In the past, hydrogen bonding for quinoid systems has been inferred indirectly from UV-vis and computational studies. In addition, it has been inferred from standard mathematical treatments based on the redox shift of the voltammetric peaks caused by the association with the hydroxyllic reagents [1,[15][16][17][18][19][20][21][22][23][37][38][39]. These studies clearly indicated that hydrogen bonding on its own can significantly alter the electrochemistry of quinoid compounds even though actual PT does not occur.…”

A Model for Characterization of Successive Hydrogen Bonding Interactions with Electrochemically Generated Charged Species. The Quinone Electroreduction in the Presence of Donor Protons

“…The number of DH molecules involved in association by hydrogen bonding, as well as the respective association constants determined in this work, could also be analyzed with theoretical calculations [51,52] or through experimental data obtained using techniques other than those electrochemical procedures described herein [52 ± 54], however, such evaluations are beyond the scope of this work.…”

Photophysical properties of [N]phenylenes

“…[17][18][19][20] The charge transfer properties of biphenylene have also found interest, and the structure of its radical cation, as well as inter-and intramolecular electron transfer in biphenylene-containing compounds have been studied. [21][22][23] As to the photophysical behaviour of the two [3]phenylenes, Niemeyer has revealed striking differences (in cyclohexane at room temperature): Whereas linear [3]phenylene (2a) was found to be non-fluorescent (Φ F < 10 -5 ), angular [3] 28 X-ray structure analysis data show also a strong alternance of the C-Cbond length in the central rings of the zig-zag [N]phenylenes. 5,29 In the present work, photophysical investigations of the linear and angular [3]phenylenes (2a), (3a), the zig-zag [4]-and [5]phenylenes (3b), (3c), and the triangular [4]phenylene (4) were performed (Fig.…”