Completely Encapsulated Oligothiophenes: Synthesis, Properties, and Single‐Molecule Conductance

Abstract

Proper shielding: Encapsulated oligothiophenes for the investigation of single‐molecule conductance are described. UV/Vis/NIR measurements of the oxidized species show the absence of intermolecular interactions between the conjugated backbones. The conductance of a single‐molecule junction was measured by modified STM techniques (see picture), and the decay constant β was determined to be 1.9 nm−1. SMU=source meter unit.

Stabilization of Charge Carriers in Picket‐Fence Polythiophenes Using Dielectric Side Chains

“…where n ′ is the number of thiophenes in the oligomers and not the monomer units (i.e., n ′=2 n ). The coefficient of the plot (3.76) is comparable to that of unsubstituted oligothiophenes (3.73) and those of other IMWs (3.68 for P1 and 3.85 for 5 n ). TD‐DFT calculations using the DFT(M06‐2X)/6‐31G(d,p) method corroborated this result (see the Supporting Information).…”

“…However, as is often problematic with such insoluble polymeric materials, thorough characterization of the polymer was not performed. Among IMWs with a similar fluorene‐based structure, Aso, Ie, and coworkers have reported the insulated oligothiophenes 5 n and 6 n for use in single‐molecule conductance measurements . In this study, we introduce a fluorene “picket” with 2,6‐dialkoxy phenyl groups that wrap around the polythoiphene backbone (Scheme b ).…”

Synthesis, Properties, and π‐Dimer Formation of Oligothiophenes Partially Bearing Orthogonally Fused Fluorene Units

“…The p-p*t ransition energies (E)o ft he oligothiophenes,e stimated from their absorption maxima, are plotted against the inverse of the number of thiophenes (1/n)i n the inset of Figure 3a. Based on the observed linear relationship, the equation for U(TU) n is determined to be E (eV) = 2.11+ +3.83/n.I ti si mportant to notet hat its slope (3.87) is almostt he same as that for fully spiro-substituted oligothiophenes( 3.85) [34] and is slightly steeper than that of nonsubstituted oligothiophenes (3.76). [37] This result clearly indicates that, despite the installation of the bulky 2-ethylhexyl groups, effective conjugation is maintainedi nt he U(TU) n conjugated system.A ss hown in Figure 3b, the absorption coefficients derived from the transitions of the fluorene unit are similarf or UTU 2 TU and UTU 3 TU because they have the same number of Tu nits, whereas the p-p*t ransition of the oligothiophene backbonesi sr edshifted with chain lengthening.Aslight blueshift was observed for UTU 3 TU comparedw ith that of U(TU) 3 consisting of the same number of thiophener ings, which is ascribable to ad ecrease in the number of electron-donating cyclopentene units.…”

Radical Cation of Star-Shaped Condensed Oligofluorenes Having Isotruxene as a Core: Importance of Rigid Planar Structure on Charge Delocalization

“…It is also revealed from the transient absorption measurement during the pulse radiolysis that the generated radical cations of CITFn were quite stable and did not decay within a millisecond time window ( Figure S2 in the Supporting Information, lower panel), probably because the backbone of CITFn makes stable radical cation formation possible and the C 6 H 4 CH 3 substituent groups at the methylene linker, which can cover the CITF backbone, inhibited the recombination process. 22 For better understanding of these absorption bands, transition energies and oscillator strengths of CITFn radical cations were calculated using TDDFT at the B3LYP/6-31G(d) level. TDDFT calculations were limited to IT, CITF1, and CITF2 because of limitation of the present facilities.…”