Protonation‐Induced Cyclocondensation of 1‐Aryl Ethynylanthraquinones: Expanding the π Conjugation

Benzo[e]pyrene Skeleton Dipyrylium Dication with a Strong Donor–Acceptor–Donor Interaction, and Its Two‐Electron Reduced Molecule

“…As shown in Figure 1, the spectrum changed in two steps, indicating that two protonation reactions occurred sequentially. First, the band corresponding to the anthraquinone moiety at 455 nm decreased, and the band characteristic of the pyrylium ring at 540 nm grew along with a broad donor-acceptor CT band [6][7][8][9][10] at 650-1450 nm with l max = 850 nm (vide infra). Subsequently, the band characteristic of the pyrylium ring at 540 nm decreased slightly with a shift in l max to 535 nm, and the broadness and intensity of the CT band increased further over the range 660-1560 nm along with a shift in l max to 960 nm .…”

“…[4] Heteroatom-containing PAHs, particularly six-membered ring structures with oxygen, are scarce [5] because of their instability. In our recent studies, we have developed a new class [6][7][8][9][10] of donoracceptor (D-A) and D-A-D molecules, in which D (ferrocenyl (Fc), diarylaminophenyl (Am), phenyldithiolene (Pdt), phenyl, m-tolyl, or p-tolyl) and A (ethynylanthraquinone (Aq)) undergo mono and double intramolecular cyclization, respectively, to give pyrylium cations. The monoprotonated pyrylium cation [1-RPyl] + has a tetracyclic structure in which oxygen is in cationic form in the p-conjugated aromatic six-membered ring.…”

“…This phenomenon can be used to lower the energy of the lowest unoccupied molecular orbital (LUMO) to allow intramolecular electron transfer. When R is a strong donor such as Fc, Am, or Pdt, a strong and broad band ascribed to charge transfer (CT) between R and Pyl + appears in the Vis/NIR region, [6][7][8][9][10] and thereby valence tau-tomers [11] are generated. The electronic structure of D-A and D-A-D molecules directly influences the molecular physical properties by controlling the electronic communication between two redox active centers in the presence of external stimuli [12][13][14] such as protons, photons, magnetic fields, or electrons, to produce molecular devices.…”

Thioacetyl-Terminated Ferrocene-Anthraquinone Conjugates: Synthesis, Photo- and Electrochemical Properties Triggered by Protonation-Induced Intramolecular Electron Transfer

“…To date, a large number of donor-acceptor assemblies with photo- and electro-active units have been constructed to study their structure-property relationships for a better understanding of the electron-transfer reactions between the donor and acceptor moieties [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ]. Recently, a π-conjugated donor-acceptor system, in which ferrocene (Fc) was used as the donor, anthraquinone (Aq) as the acceptor, and ethynylene as the π-conjugated linker, has been studied in detail in solution and solid form by our group [ 22 , 23 , 24 , 25 , 26 , 27 ]. It is interesting that the conjugated Fc-Aq compounds are sensitive to the external stimulus of protonation, leading to an expanded π-conjugated system formed by a cyclocondensation reaction and simultaneously displaying significant changes in their optical, structural, and magnetic properties.…”

“…It is interesting that the conjugated Fc-Aq compounds are sensitive to the external stimulus of protonation, leading to an expanded π-conjugated system formed by a cyclocondensation reaction and simultaneously displaying significant changes in their optical, structural, and magnetic properties. Moreover, the expanded π-conjugation promotes intramolecular electron transfer from donor to acceptor and results in a temperature-dependent valence tautomerization (VT) between two redox-active sites ( Scheme 1 ) [ 26 , 27 ].…”