Synthesis, Photophysical, and (Spectro)Electrochemical Properties of New Benzo[1,2-c][1,2,5]thiadiazoles and Benzo[1,2-d][1,2,3]triazoles Fused with Two Thiazole Rings.

Acylation of benzo[c][1,2,5]thiadiazole-4,7-diamine and 2-hexyl-2H-benzo[d][1,2,3]triazole-4,7-diamine with aromatic acid halides furnished the corresponding N,N'-diamides, which were converted into N,N'-dithioamides by reacting with Lawesson's reagent. A method was developed for the preparation of previously unknown fused systems, dithiazolobenzo[1,2-c][1,2,5]thiadiazoles and dithiazolobenzo[1,2-d][1,2,3]triazoles, by oxidative photochemical cyclization of N,N'-dithioamides. The photophysical and (spectro)electrochemical properties of the obtained compounds and their polymer films electrochemically deposited on ITO were studied. The optical contrast and response time of the synthesized oligomers were determined. The results obtained allow us to consider these substances as promising candidates for electrochromic devices.

Photochemical Synthesis and Electrochemical and Photophysical Properties of 2,7-Diarylbenzo[1,2-d:4,3-d']bis(thiazoles).

This article focuses on the development of practical approaches to the preparation of benzo[1,2-d:4,3-d']bis(thiazoles) using blue light-induced photochemical cyclization of N,N'-(1,4-aryl)dithioamides in the presence of p-chloranil as a mild oxidant. The proposed method allows to obtain benzo[1,2-d:4,3-d']bis(thiazoles) containing donor substituents in the conjugated chain. Photophysical and (spectro)electrochemical properties of 2,6-di([2,2'-bithiophen]-5-yl)benzo[1,2-d:4,3-d']bis(thiazole) and -benzo[1,2-d:4,5-d']bis(thiazole) are studied in detail. The properties of the synthesized compounds suggest their potential applications for organic electronics.

Rearrangement of 7-Aryloxazolo[5,4-b]pyridines to Benzo[c][1,7]naphthyridine-4(3H)-ones and Thieno[3,2-c][1,7]naphthyridine-6(7H)-ones.

In this work, we describe the development of the rearrangement for 7-aryl-substituted oxazolo[5,4-b]pyridines treated with aluminum chloride into synthetically hard-to-reach benzo[c][1,7]naphthyridinones. The discovered rearrangement is applied to a variety of electron-rich (hetero)arene substrates. It offers the advantages of mild conditions (90 °C temperature), fast reaction rates (<4 h), compatibility with air moisture, and the use of inexpensive commercial reagents. The proposed reaction mechanism and key elementary reaction acts were studied in detail using quantum chemical calculations. The photophysical properties of the synthesized compounds were studied by steady-state UV-vis spectroscopy.

Synthesis of Bis([2,2'-bithiophen]-5-yl)-Substituted Oligothiadiazoles: Effect of the Number of Acceptor Units on Electrochemical and Spectroscopic Properties.

1,3,4-Thiadiazole, 2,2'-bi(1,3,4-thiadiazole), 2,2':5',2″-ter(1,3,4-thiadiazole), and 2,2':5',2″:5″,2‴-quater(1,3,4-thiadiazole) symmetrically disubstituted with 3-alkyl-(2,2'-bithiophen)-5-yl were synthesized by new procedures using readily available ethyl 3-alkyl-(2,2'-bithiophene)-5-carboxylate as a convenient substrate. These new compounds with a fixed number of donor rings and increasing number of acceptor rings showed very interesting, tunable redox properties. In particular, they exhibited electron affinities (EAs) ranging from -3.06 to -3.83 eV, reaching EA values desired for air-operating n-type organic semiconductors. Their electrochemically determined ionization potentials were only moderately dependent on the number of thiadiazole rings, varying from 5.83 to 6.01 eV. Emission spectra of these compounds could also be tuned in a wide range (from 470 to 600 nm). Spectroscopic and electrochemical data were confirmed by density functional theory calculations demonstrating full consistency.

Effect of donor to acceptor ratio on electrochemical and spectroscopic properties of oligoalkylthiophene 1,3,4-oxadiazole derivatives.

A structure-property study across a series of donor-acceptor-donor structures composed of mono- and bi-(1,3,4-oxadiazole) units symmetrically substituted with alkyl functionalized bi-, ter- and quaterthiophene segments is presented. Synthetically tailoring the ratio of electron-withdrawing 1,3,4-oxadiazole to electron-releasing thiophene units and their alkyl grafting pattern permitted us to scrutinize the impact of these structural factors on the redox, absorptive and emissive properties of these push-pull molecules. Contrasting trends of redox potentials were observed, with the oxidation potential closely following the donor-to-acceptor ratio, whereas the reduction potential being tuned independently by either the number of acceptor units or the conjugation length of the donor-acceptor system. Increasing the thiophene unit contribution delivered a shift from blue to green luminescence, while the structural rigidity afforded by intramolecular non-covalent interactions between 1,3,4-oxadiazole and the thiophene moieties has been identified as the prime factor determining the emission efficiency of these molecules. All six structures investigated electro-polymerize easily, yielding electroactive and electrochromic polymers. The polymer doping process is largely influenced by the length of the oligothiophene repeating unit and the alkyl chain grafting density. Polymers with relatively short oligothiophene segments are able to support polarons and polaron-pairs, whereas those with segments longer than six thiophene units could also stabilize diamagnetic charge carries - bipolarons. Increasing the alkyl chain grafting density improved the reversibility and broadened the working potential window of the p-doping process. Stable radical anions have also been investigated, bringing detailed information about the conjugation pattern of these electron-surplus species. This study delivers interesting clues towards the conscious structural design of bespoke frontier energy level oligothiophene functional materials and their polymers by incorporating a structurally matching 1,3,4-oxadiazole unit.

Star-Shaped Conjugated Molecules with Oxa- or Thiadiazole Bithiophene Side Arms.

Star-shaped conjugated molecules, consisting of a benzene central unit symmetrically trisubstituted with either oxa- or thiadiazole bithiophene groups, were synthesized as promising molecules and building blocks for application in (opto)electronics and electrochromic devices. Their optical (Eg (opt)) as well as electrochemical (Eg (electro)) band gaps depended on the type of the side arm and the number of solubilizing alkyl substituents. Oxadiazole derivatives showed Eg (opt) slightly below 3 eV and by 0.2 eV larger than those determined for thiadiazole-based compounds. The presence of alkyl substituents in the arms additionally lowered the band gap. The obtained compounds were efficient electroluminophores in guest/host-type light-emitting diodes. They also showed a strong tendency to self-organize in monolayers deposited on graphite, as evidenced by scanning tunneling microscopy. The structural studies by X-ray scattering revealed the formation of supramolecular columnar stacks in which the molecules were organized. Differences in macroscopic alignment in the specimen indicated variations in the self-assembly mechanism between the molecules. The compounds as trifunctional monomers were electrochemically polymerized to yield the corresponding polymer network. As shown by UV/Vis-NIR spectroelectrochemical studies, these networks exhibited reversible electrochromic behavior both in the oxidation and in the reduction modes.

Synthesis of new, highly luminescent bis(2,2'-bithiophen-5-yl) substituted 1,3,4-oxadiazole, 1,3,4-thiadiazole and 1,2,4-triazole.

A new synthetic approach towards the preparation of functionalised, soluble, donor-acceptor (DA) alkylbithiophene derivatives of oxadiazole, thiadiazole and triazole is reported. Taking advantage of the Fiesselmann reaction, reactive bithiophene synthons having alkyl or alkoxy substituents at designated positions are prepared. Following a synthetic strategy, featuring the bottom-up approach, sequential structural elements are built, starting from a simple thiophene compound, until the target molecule is obtained, all in good yield. Supplementing the well established methods of oxadiazole and thiadiazole synthesis, efficient ring closure reaction affording a 4H-1,2,4-triazole unit is presented. All target ambipolar compounds display strong photoluminescence with measured quantum yields up to 0.59. Modification of the demonstrated synthetic routes may be exploited for the preparation of longer, specifically functionalised oligothiophenes, coupled to other heteroaromatic cores.

A simple and efficient synthesis of substituted 2,2'-bithiophene and 2,2':5',2″-terthiophene.

A simple and efficient approach is developed for the synthesis of substituted 2,2'-bithiophene- and 2,2':5',2″-terthiophene-5-carboxylic acids and esters which is based on thiophene ring closure in the Fiesselmann reaction. Using this method, derivatives containing a long alkyl chain with or without an end functional group or an aryl substituent can be conveniently prepared.