3,4-Ethylenedioxythiophene in planarizable push-pull oligothiophenes

Light-Responsive Oligothiophenes Incorporating Photochromic Torsional Switches

We present a quaterthiophene and sexithiophene that can reversibly change their effective π-conjugation length through photoexcitation. The reported compounds make use of light-responsive molecular actuators consisting of an azobenzene attached to a bithiophene unit by both direct and linker-assisted bonding. Upon exposure to 350 nm light, the azobenzene undergoes trans-to-cis isomerization, thus mechanically inducing the oligothiophene to assume a planar conformation (extended π-conjugation). Exposure to 254 nm wavelength promotes azobenzene cis-to-trans isomerization, forcing the thiophenic backbones to twist out of planarity (confined π-conjugation). Twisted conformations are also reached by cis-to-trans thermal relaxation at a rate that increases proportionally with the conjugation length of the oligothiophene moiety. The molecular conformations of quaterthiophene and sexithiophene were characterized by using steady-state UV-vis spectroscopy, X-ray crystallography and quantum-chemical modeling. Finally, we tested the proposed light-responsive oligothiophenes in field-effect transistors to probe the photo-induced tuning of their electronic properties.

The Synthesis and Photophysical Properties of Weakly Coupled Diketopyrrolopyrroles

Three centrosymmetric diketopyrrolopyrroles possessing either two 2-(2′-methoxyphenyl)benzothiazole or two 2-(2′-methoxyphenyl)benzoxazolo-thiophene scaffolds were synthesized in a straightforward manner, and their photophysical properties were investigated. Their emission was significantly bathochromically shifted as compared with that of simple DPPs reaching 650 nm. Judging from theoretical calculations performed with time-dependent density functional theory, in all three cases the excited state was localized on the DPP core and there was no significant CT character. Consequently, emission was almost independent of solvents’ polarity. DPPs possessing 2,5-thiophene units vicinal to DPP core play a role in electronic transitions, resulting in bathochromically shifted absorption and emission. Interestingly, as judged from transient absorption dynamics, intersystem crossing was responsible for the deactivation of the excited states of DPPs possessing para linkers but not in the case of dye bearing meta linker.

Conjugated Polymers for Assessing and Controlling Biological Functions

The field of organic bioelectronics is advancing rapidly in the development of materials and devices to precisely monitor and control biological signals. Electronics and biology can interact on multiple levels: organs, complex tissues, cells, cell membranes, proteins, and even small molecules. Compared to traditional electronic materials such as metals and inorganic semiconductors, conjugated polymers (CPs) have several key advantages for biological interactions: tunable physiochemical properties, adjustable form factors, and mixed conductivity (ionic and electronic). Herein, the use of CPs in five biologically oriented research topics, electrophysiology, tissue engineering, drug release, biosensing, and molecular bioelectronics, is discussed. In electrophysiology, implantable devices with CP coating or CP-only electrodes are showing improvements in signal performance and tissue interfaces. CP-based scaffolds supply highly favorable static or even dynamic interfaces for tissue engineering. CPs also enable delivery of drugs through a variety of mechanisms and form factors. For biosensing, CPs offer new possibilities to incorporate biological sensing elements in a conducting matrix. Molecular bioelectronics is today used to incorporate (opto)electronic functions in living tissue. Under each topic, the limits of the utility of CPs are discussed and, overall, the major challenges toward implementation of CPs and their devices to real-world applications are highlighted.

The impact of interplay between electronic and steric effects on the synthesis and the linear and non-linear optical properties of diketopyrrolopyrrole bearing benzofuran moieties

Benzofuran has been proven to be the versatile substituent for tuning the optics of diketopyrrolopyrroles.

Design and Synthesis of Mixed Oligomers with Thiophenes, Dithienothiophene S,S-Dioxides, Thieno[3,4]pyrazines and 2,1,3-Benzothiadiazoles: Flipper Screening for Mechanosensitive Systems

Monomers with large surface area and high quantum yield, that is fluorescent flippers, have been engineered into twisted push–pull oligomers to create membrane probes with high mechanosensitivity and long fluorescence lifetime. Here, the synthesis and characterization of thieno[3,4]pyrazines and 2,1,3-benzothiadiazoles are described in comparison with the original dithienothiophene S,S-dioxides. Dithienothiophene S,S-dioxide flippers are confirmed as the best reported so far, and poor results with single flipper probes support that two flippers are needed for the probe to really “swim”, that is, for high mechanosensitivity.

Planarizable push–pull oligothiophenes: in search of the perfect twist

The “twistome” of push–pull oligothiophenes is covered comprehensively. Particular emphasis is on the development of conceptually innovative fluorescent membrane probes.

The structural basis for optimal performance of oligothiophene-based fluorescent amyloid ligands: conformational flexibility is essential for spectral assignment of a diversity of protein aggregates

Protein misfolding diseases are characterized by deposition of protein aggregates, and optical ligands for molecular characterization of these disease-associated structures are important for understanding their potential role in the pathogenesis of the disease. Luminescent conjugated oligothiophenes (LCOs) have proven useful for optical identification of a broader subset of disease-associated protein aggregates than conventional ligands, such as thioflavin T and Congo red. Herein, the molecular requirements for achieving LCOs able to detect nonthioflavinophilic Aβ aggregates or non-congophilic prion aggregates, as well as spectrally discriminate Aβ and tau aggregates, were investigated. An anionic pentameric LCO was subjected to chemical engineering by: 1) replacing thiophene units with selenophene or phenylene moieties, or 2) alternating the anionic substituents along the thiophene backbone. In addition, two asymmetric tetrameric ligands were generated. Overall, the results from this study identified conformational freedom and extended conjugation of the conjugated backbone as crucial determinants for obtaining superior thiophene-based optical ligands for sensitive detection and spectral assignment of disease-associated protein aggregates.