Planar, Twisted, or Curved Extended Tetrathiafulvalenes with Polycyclic Aromatic Hydrocarbon Cores Featuring Five-Membered Rings

Tetrathiafulvalene (TTF) and polycyclic aromatic hydrocarbons (PAHs) represent two distinct classes of redox-active chromophores. By merging these two classes in so-called extended tetrathiafulvalenes, new physico-chemical characteristics emerge. Here in this study, we summarize the properties of such PAH-extended TTFs for which the PAH core incorporates five-membered carbo-cyclic rings together with six-, seven-, and/or eight-membered rings. A key structural motif of these molecules is the planar 2-(1H-inden-1-ylidene)-1,3-dithiole unit. Fusing two such units directly together or via various one- or two-dimensional PAH scaffolds has during the past decade provided a large selection of planar, twisted, or curved extended TTFs. Strong associations of radical cations are in some cases obtained, corresponding to redox-controlled self-assembly in solution, and these associations have allowed for the ready generation of semi-conducting salts by electrocrystallization. Some molecules exhibit remarkable multiredox behavior and can reversibly reach high cationic states, and, in some cases, also anionic states. Several structural examples also reveal how closed-shell versus open-shell characters of the dication states can be controlled by the nature of the PAH core, particularly by the number of Clar sextets within the core.

Phenyldithiafulvene-Substituted Ferrocene Derivatives as Redox-Regulated Molecular Switches

We designed a new type of redox-active molecular triad in which two electron-donating dithiafulvene (DTF) groups are connected to a central ferrocene (Fc) hinge unit through phenylene linkers. Three structural isomers of the (DTF)2-Fc system were synthesized through Suzuki-Miyaura cross-coupling followed by phosphite-promoted olefination reactions. The molecular structures and solid-state properties of these compounds were investigated by X-ray single-crystallographic analysis. Their electronic absorption and electrochemical properties in the solution phase were examined using UV-vis spectroscopy and cyclic voltammetry. Our studies showed that these compounds possess multistage redox activities due to the presence of electron-donating DTF and Fc groups, while detailed redox behaviors are dependent on the substitution patterns and steric crowdedness of each compound. To gain deeper insight, we performed density functional theory (DFT) and molecular dynamics (MD) simulations to examine the conformational and electronic properties of these compounds in neutral and different oxidation states. Furthermore, the para-substituted (DTF)2-Fc was found to show intriguing supramolecular interactions with γ-cyclodextrin.

DFT investigations of phenyldithiafulvene dimers at different oxidation states

Oxidative dimerization of aryl-substituted dithiafulvenes (Ar-DTFs) presents an efficient C-C bond forming method for the preparation of diverse redox-active π-conjugated molecules and conductive polymers. Previous experimental data indicated a reaction pathway in which direct combination of two Ar-DTF radical cations is a key step. However, mechanistic details about how Ar-DTF dimers are formed under different oxidation states have not yet been clearly established prior to this work. The assembly of two Ar-DTF molecules generates a vast conformational and configurational landscape, which is quite complex but fundamentally important for understanding the dimerization mechanism. To cast a deep insight into this aspect, we have performed density functional theory (DFT) calculations at the M06-2X/Def2-SVP level of theory to thoroughly investigate the potential energy surfaces (PESs) of various dimers of a phenyl-substituted dithiafulvene (Ph-DTF) in the mixed-valence radical cation and dication states. Key stationary points in these PESs, including minimum-energy conformers (π-dimers and σ-dimers) as well as the transition states connected to them, were examined and compared. We have also calculated the binding energies of these dimers to evaluate the energetic driving forces for their formation. Based on our computational results, the roles that various Ph-DTF dimers play in different pathways of oxidative dimerization have been clarified.

Donor-Acceptor Fluorophores and Macrocycles Built Upon Wedge-Shaped π-Extended Phenanthroimidazoles

A class of wedge-shaped organic π-fluorophores featuring a 6,9-diphenyl-substituted phenanthroimidazole (PI) core was designed, synthesized, and characterized. Among them, a π-extended PI derivative containing two electron-withdrawing aldehyde groups was found to exhibit versatile solid-state packing properties as well as strong solvatofluorochromism in different organic solvents. Another PI derivative that was functionalized with two electron-donating 1,4-dithiafulvenyl (DTF) end groups showed versatile redox reactivities and quenched fluorescence. Treatment of this wedge-shaped bis(DTF)-PI compound with iodine resulted in oxidative coupling reactions, leading to the formation of intriguing macrocyclic products that carry redox-active tetrathiafulvalene vinylogue (TTFV) moieties in their structures. Mixing the bis(DTF)-PI derivative with fullerene (C₆₀ or C₇₀) in an organic solvent resulted in substantial fluorescence enhancement (turn-on). In this process, fullerene acted as a photosensitizer to generate singlet oxygen, which in turn induced oxidative C = C bond cleavages and converted nonfluorescent bis(DTF)-PI into highly fluorescent dialdehyde-substituted PI. Treatment of TTFV-PI macrocycles with a small amount of fullerene also led to a moderate degree of fluorescence enhancement, but this is not because of photosensitized oxidative cleavage reactions. Instead, competitive photoinduced electron transfer from TTFV to fullerene can be attributed to their fluorescence turn-on behavior.

Studies of a bola-type bis(dithiafulvene) molecular system: synthesis, crystal structure, and electrochemical properties

A bis(dithiafulvene) compound that contains a 1,3-diphenoxypropane central unit was designed and investigated in this work.

An Active Catalyst System Based on Pd (0) and a Phosphine-Based Bulky Ligand for the Synthesis of Thiophene-Containing Conjugated Polymers

To address the limitations of conventional Pd catalysts in the polymerization of thiophene-containing conjugated polymers, an active catalyst system based on Pd (0) and a phosphine-based bulky ligand, L1, is explored systematically in Suzuki–Miyaura polymerizations using thiophene boronic acid pinacol ester as one of the monomers. This active catalyst is found very efficient in synthesizing a series of thiophene-containing linear and hyperbranched conjugated polymers. First, as a model example, coupling reactions between electron-rich/moderately hindered aryl or thienyl halides and thiophene boronic acid pinacol ester give excellent yields with lower catalyst loading and can be completed in a shorter reaction time relative to Pd(PPh₃)₄. Notably, high molecular weight thiophene-containing polymers are successfully synthesized by Suzuki–Miyaura polycondensation of 2,5-thiophene bis(boronic acid) derivatives with different dibromo- and triple bromo-substituted aromatics in 5–15 min.

A Comparative Study of Redox-Active Dithiafulvenyl-Functionalized 1,3,6,8-Tetraphenylpyrene Derivatives

A series of 1,3,6,8-tetraphenylpyrene (TPPy) derivatives substituted with redox-active 1,4-dithiafulvenyl (DTF) groups was synthesized and characterized. The conformational properties of these DTF-TPPys and their TPPy precursors were assessed by X-ray single-crystal and nuclear magnetic resonance analyses. Their electronic and redox properties were examined by ultraviolet-visible absorption, fluorescence, and cyclic voltammetric analyses. The DTF substitution was found to strongly modify the absorption, emission, and electrochemical properties, while detailed effects can be linked to substitution patterns and alkyl side chains attached to the DTF groups. Furthermore, the DTF-TPPy derivatives showed sensitivity to acids; in particular, the vinylic proton of DTF group could undergo efficient proton/deuterium exchange with D₂O in an acidic medium.

Donor/acceptor substituted dithiafulvenes and tetrathiafulvalene vinylogues: electronic absorption, crystallographic, and computational analyses

The structural, electronic, and crystallographic properties of nitrophenyl and methoxyphenyl-substituted dithiafulvenes and tetrathiafulvalene vinylogues were systematically investigated by experimental and computational approaches.

Synthesis and characterization of bis(dithiafulvenyl)-substituted fluorenones and fluorenylidene-1,3-dithioles

A series of π-conjugated oligomers containing redox-active dithiafulvenyl (DTF) end groups and fluorenone/fluorenylidene-1,3-dithiole central units was synthesized and their structural, electronic, and electrochemical properties were investigated.