190723-14-9Relevant articles and documents
Oligothiophene-Bridged Conjugated Covalent Organic Frameworks
Keller, Niklas,Bessinger, Derya,Reuter, Stephan,Calik, Mona,Ascherl, Laura,Hanusch, Fabian C.,Auras, Florian,Bein, Thomas
, p. 8194 - 8199 (2017/06/27)
Two-dimensional covalent organic frameworks (2D-COFs) are crystalline, porous materials comprising aligned columns of π-stacked building blocks. With a view toward the application of these materials in organic electronics and optoelectronics, the construction of oligothiophene-based COFs would be highly desirable. The realization of such materials, however, has remained a challenge, in particular with respect to laterally conjugated imine-linked COFs. We have developed a new building block design employing an asymmetric modification on an otherwise symmetric backbone that allows us to construct a series of highly crystalline quaterthiophene-derived COFs with tunable electronic properties. Studying the optical response of these materials, we have observed for the first time the formation of a charge transfer state between the COF subunits across the imine bond. We believe that our new building block design provides a general strategy for the construction of well-ordered COFs from various extended building blocks, thus greatly expanding the range of applicable molecules.
Alternating donor/acceptor repeat units in polythiophenes. Intramolecular charge transfer for reducing band gaps in fully substituted conjugated polymers
Zhang, Qing T.,Tour, James M.
, p. 5355 - 5360 (2007/10/03)
This paper describes a method to limit the band gap widening that occurs in fully substituted conjugated polymers. This is done by constructing step growth [AB] polymers where the A-units are electron rich and the B-units are electron deficient. The thiophene-based polymers were prepared by modified Stille polymerizations using Pd(0)/CuI catalyst systems in which aryldibromides were coupled with aryldistannanes. The donor units were N,N′-(bis-tert-butoxycarbonyl)-3,4-diaminothiophene, N,N′-(bis-tert-butoxycarbonyl)-N,N′-(dimethyl)-3,4-diaminothiophene, 3,4-diaminothiophene, or 3,4-dialkoxythiophenes while the acceptor units were 3,4-dinitrothiophene, 3,4-(N-n-butylimido)thiophene, or 3,4-diketone-containing thiophenes. The optical spectra showed λmax values ranging from 400 to 676 nm (solution) and 400-768 (film) for these fully substituted polythiophenes, consistent with significant decreases in the band gaps. Intramolecular charge transfer character between the consecutive units explained the lowering of the band gaps. Two polymer systems based solely on electron deficient thiophenes were prepared via an Ullmann coupling which had optical absorption maxima that were in the range of 300-340 nm; considerably smaller than the λmax values for the donor/acceptor systems. Several model trimers were prepared which had significantly shorter wavelength optical absorptions than their corresponding polymers, thus confirming the need for the extended polymeric backbones.
