New Conjugated Oligothiophenes Containing the Unique Arrangement of Internal Adjacent [All]-S,S-Oxygenated Thiophene Fragments

Understanding the effects of sulfur di-oxidation and side chain engineering on absorption and fluorescence of oligothiophene: A theoretical study

Oligothiophene and its derivatives have broad applications in organic electronics because of its stability, easy functionalization, and broad color adjustability, and excellent charge carrier mobility. However, the effects of sulfur di-oxidation and side alkyl chains on the absorption and fluorescence of oligothiophene are still not well understood. In this article, we have applied density functional theory (DFT) and time-dependent DFT (TDDFT) to study a series of quinquethiophene compounds functionalized with S,S-dioxide and side alkyl chains, which were experimentally synthesized. Through benchmark calculations, we have found a reliable computational method, and successfully reproduced experimental UV-Vis absorption and fluorescence emission spectra well. Furthermore, the calculated reorganization energy of these molecules could explain the energy differences between absorption and emission spectra. Last but not lease, we also have calculated the fluorescence quantum yield efficiency (Фfl) of two compounds with good planarity in this series, and the trend of calculated values is consistent with experiment. Our work gives an insight to the effects of sulfur di-oxidation and side chain engineering on absorption and fluorescence of oligothiophene.

Palladium-Catalyzed C2-Selective Direct Arylation of Benzo[b]thiophene 1,1-Dioxides with Arylboronic Acids

A novel oxidative cross-coupling of benzo[b]thiophene 1,1-dioxides with arylboronic acids was reported. The efficient reaction occurred at the C2-position via C-H activation, followed by Pd(II)-catalyzed arylation. Furthermore, a series of C2-arylated products with significant photoluminescence properties have been synthesized and characterized, which illustrates the potential applications of our method in the aggregation-induced emission field.

Palladium-Catalyzed C2-Selective Oxidative Olefination of Benzo[b]thiophene 1,1-Dioxides with Styrenes and Acrylates

Here, we disclose a novel Pd(II)-catalyzed oxidative Heck reaction of benzo[b]thiophene 1,1-dioxides with styrenes and acrylates. This transformation features broad functional group tolerance and high C2 selectivity. Furthermore, the photoluminescence properties of C-2 alkenylated products have been characterized, which illustrates the potential usefulness of our protocol in constructing π-conjugated fluorescent molecules.

Excited-state engineering of oligothiophenes via phosphorus chemistry towards strong fluorescent materials

Due to efficient intersystem crossing (ISC), combined with efficient non-radiative processes of the triplet excited state, oligothiophenes generally exhibit very weak photoluminescence. Phosphorus (P)-bridged terthiophenes (P-terThs) and phosphorus (P)-bridged bithiophenes (P-biThs) were synthesized. The diverse and well-defined P-chemistry has been applied to fine tune the photophysical properties of these materials. The asymmetric electronic coupling between the P-center and terThs suppressed the electronic interactions of two terTh and biTh moieties in the ground state S₀. Particularly, P-terThs and P-biThs having a positively charged P(+)-center induce pronounced asymmetric electronic environments on the two terThs and two biThs, respectively, which allows relaxation from the initial excited state via symmetry breaking charge transfer (SBCT) to give the charge separated state S_SBCT. P-terThs and P-biThs having a positively charged P(+)-center exhibit stronger SBCT than others, which may result in a weaker ISC of oligothiophenes, and consequently lead to the photoluminescence quantum yields (PLQYs) being as high as 71% and 39%, respectively. The current study uncovered detailed insights on the effects of phosphorus chemistry on the SBCT of oligothiophenes and their resulting effects on the photophysical properties of P-bridged oligothiophenes, which have not been previously addressed in oligothiophenes.

[All]-S,S-dioxide Oligo-Thienylenevinylenes: Synthesis and Structural/Electronic Shapes from Their Molecular Force Fields

Oligo-S,S-dioxothienylenevinylenes have been prepared by transferring oxygen atoms to the sulfur atoms using the HOF⋅CH₃ CN complex. Their photophysical properties are presented in comparison with their thiophenevinylene congeners. Together with their vibrational properties and molecular force fields, this study allows for the interpretation of the alteration of aromaticity and inter-ring exocyclic π-conjugation in this series.

HOF·CH3CN: probably the best oxygen transfer agent organic chemistry has to offer

The complex HOF·CH3CN is readily obtained by bubbling dilute fluorine into aqueous acetonitrile solution. It does not have to be purified or isolated, and its solution can react as is, after the concentration has been establish by any iodometric method. It is the only reagent possessing a distinctive positive oxygen species. This enables electrophilic oxygen transfer with results no other reagent can match. HOF·CH3CN demonstrates its ability in epoxidations that either could not be performed before or could only obtained 5 orders of magnitude slower. This complex is also an excellent tool for oxygenation of compounds at the α position of a carbonyl, including the synthesis of some hard-to-come-by indanediones, which are important for fingerprint visualization on paper. HOF·CH3CN proves itself as a very efficient reagent for oxygenating tertiary nitrogen atoms both in aliphatic (including azides) and in aromatic amines, which could not be accomplished despite many attempts in the last 50 years. Oxygenation of two tertiary nitrogen atoms in the same molecule also becomes feasible as demonstrated for various phenanthrolines, bipyridines, diazafluorenones, and quinoxalines. It was also used to oxygenate primary amines, and because of the exceptionally mild conditions, it could transform vicinal aliphatic diamines to vicinal dinitro derivatives as well as amino acids to the corresponding nitro ones, practically unknown transformations before. Its ability to react with azines and hydrazones and convert them to the original carbonyls helped to establish these groups as good protecting tools for a variety of carbonyls. HOF·CH3CN excels in oxygenation of various sulfur and selenium compounds that could not be oxygenated in the past. The selectivity of the oxidation is quite good, and if there are alcohols, double bonds, and sulfides in the same molecule, usually the sulfur atom will be attacked first. Of special interest is the reaction with oligothiophenes resulting at will in either [all]-S,S-dioxooligothiophenes or in partially oxygenated ones. Some of these last derivatives have the narrowest HOMO-LUMO gap of all oligothiophenes tested, a very desirable feature. This reagent can also oxidize thiols or disulfides to either sulfonic or sulfinic acids at will, all in seconds and in very high yields. Since the oxygen atom of HOF·CH3CN originates in water, it is very easy and relatively inexpensive to introduce the heavy oxygen isotope in many sites of a variety of molecules, some of them quite important. The (18)O tirapazamine and any desirable alcohol, R(Ar)(18)OH, are two examples.

Dearomatization-induced transannular cyclization: synthesis of electron-accepting thiophene-S,S-dioxide-fused biphenylene

The transannular cyclization of dehydroannulenes bearing several alkyne moieties in close proximity is a powerful synthetic method for producing polycyclic aromatic hydrocarbons. We report that the reactivity can be switched by the aromaticity of the ring skeletons fused with the dehydroannulene core. Thus, while thiophene-fused bisdehydro[12]annulene 1 was handled as a stable compound in the air at room temperature, the oxidation with m-chloroperbenzoic acid from the aromatic thiophene rings to the nonaromatic thiophene-S,S-dioxides induced the transannular cyclization, even at room temperature, which was completed within 1 day to produce the formal [2 + 2] cycloadduct 3. This is in stark contrast to the fact that the thermal cyclization of 1 itself required heating at 80 °C for 9 days for completion. Experimental and theoretical studies indicate that the oxidation of even one thiophene ring in 1 sufficiently decreases the activation barrier for the transannular cyclization that proceeds through the 8π and 4π electrocyclic reaction sequence. The thiophene-S,S-dioxide-fused biphenylene 3 thus produced exhibits a set of intriguing properties, such as a higher electron affinity (E1/2 = -1.17 V vs Fc and Fc(+)) and a stronger fluorescence (ΦF = 0.20) than the other relevant biphenylene derivatives, which have electron-donating and nonfluorescent characteristics.

Bandgap engineering through controlled oxidation of polythiophenes

The use of Rozen's reagent (HOF⋅CH3 CN) to convert polythiophenes to polymers containing thiophene-1,1-dioxide (TDO) is described. The oxidation of polythiophenes can be controlled with this potent, yet orthogonal reagent under mild conditions. The oxidation of poly(3-alkylthiophenes) proceeds at room temperature in a matter of minutes, introducing up to 60 % TDO moieties in the polymer backbone. The resulting polymers have a markedly low-lying lowest unoccupied molecular orbital (LUMO), consequently exhibiting a small bandgap. This approach demonstrates that modulating the backbone electronic structure of well-defined polymers, rather than varying the monomers, is an efficient means of tuning the electronic properties of conjugated polymers.

Synthesis of thiophene 1,1-dioxides and tuning their optoelectronic properties

A 2,5-bis(tributylstannyl)thiophene 1,1-dioxide was prepared from 2,5-bis(trimethylsilyl)thiophene 1,1-dioxide, bis(tributyltin) oxide, and tetrabutylammonium fluoride (TBAF). The 2,5-bis(tributylstannyl)thiophene 1,1-dioxide and a 2,5-diiodothiophene 1,1-dioxide were utilized in a series of Stille cross-coupling reactions to afford thiophene 1,1-dioxides with either electron-donating or electron-withdrawing substituents. Electron-withdrawing groups greatly facilitate the reduction of these sulfone heterocycles, and -C6H4-p-NO2 substituents produce a 510 mV shift as compared to a thiophene 1,1-dioxide with two phenyl groups.