Phenanthrothiophene-Triazine Star-Shaped Discotic Liquid Crystals: Synthesis, Self-Assembly, and Stimuli-Responsive Fluorescence Properties.

Lipophilic biphenylthiophene- and phenanthrothiophene-triazine compounds, BPTTn and CPTTn, respectively, were prepared by a tandem procedure involving successive Suzuki-Miyaura coupling and Scholl cyclodehydrogenation reactions. These compounds display photoluminescence in solution and in thin film state, solvatochromism with increasing solvent's polarity, as well as acidochromism and metal ion recognition stimuli-responsive fluorescence. Protonation of BPTT10 and CPTT10 by trifluoroacetic acid results in fluorescence quenching, which is reversibly restored once treated with triethylamine (ON-OFF switch). DFT computational studies show that intramolecular charge transfer (ICT) phenomena occurs for both molecules, and reveal that protonation enhances the electron-withdrawing ability of the triazine core and reduces the band gap. This acidochromic behavior was applied to a prototype fluorescent anti-counterfeiting device. They also specifically recognize Fe3+ through coordination, and the recognition mechanism is closely related to the photoinduced electron transfer between Fe3+ and BPTT10/CPTT10. CPTTn self-assemble into columnar rectangular (Colrec) mesophase, which can be modulated by oleic acid via the formation of a hydrogen-bonded supramolecular liquid crystal hexagonal Colhex mesophase. Finally, CPTTn also form organic gels in alkanes at low critical gel concentration (3.0 mg/mL). Therefore, these star-shaped triazine molecules possess many interesting features and thus hold great promises for information processing, liquid crystal semiconductors and organogelators.

Mesomorphism Modulation of Perfluorinated Janus Triphenylenes by Inhomogeneous Chain Substitution Patterns.

Two isomeric series of compounds with "inverted" chains' substitution patterns, 7,10-dialkoxy-1,2,3,4-tetrafluoro-6,11-dimethoxytriphenylene and 6,11-dialkoxy-1,2,3,4-tetrafluoro-7,10-dimethoxytriphenylene, labelled respectively p-TPFn and m-TPFn, and two non-fluorinated homologous isomers, 3,6-dibutoxy-2,7-dimethoxytriphenylene and 2,7-dibutoxy-3,6-dimethoxytriphenylene, p-TP4 and m-TP4, respectively, were synthesized in three steps and obtained in good yields by the efficient transition-metal-free, fluoroarene nucleophilic substitution via the reaction of appropriate 2,2'-dilithium biphenylenes with either perfluorobenzene, C6 F6 , to yield p-TPFn and m-TPFn, or o-difluorobenzene, C6 H4 F2 , for p-TP4 and m-TP4, respectively. The single-crystal structures of p-TPF4, m-TPF4 and p-TP4, unequivocally confirmed that the cyclization reactions occurred at the expected positions, and that the fluorinated molecules stack up into columns with short separation, a propitious situation for the emergence of columnar mesophases. The mesomorphous properties were found to be greatly affected by both chains' length and positional isomerism: a Colhex phase is found for p-TPF4 and m-TPF4, but mesomorphism vanishes in p-TPF6, and changes for the isomeric homologs m-TPFn, with the induction for n≥6 of a lamello-columnar phase, LamColrec . As expected, both non-fluorinated compounds are deprived of mesomorphism. These compounds emit blue-violet colour in solution, independently of the chains' substitution pattern, and the absolute fluorescence quantum yields can reach up to 46 %. In thin films, fluorescence is slightly redshifted.

Synthesis and mesomorphic properties of "side-on" hybrid liquid crystalline silsesquioxanes.

Novel hybrid silsesquioxane-based liquid crystalline derivatives with varied lengths of spacers and tails have been synthesized by hydrosilylation reactions of octakis(dimethylsiloxy)silsesquioxane and side-on mesogens via a platinum catalyst. The thermal behavior of three types of silsesquioxane-based liquid crystals (LCs), differentiated by the molecular structure of mesogens, was investigated by differential scanning calorimetry (DSC) and polarising optical microscopy (POM). Temperature-dependent small and wide-angle X-ray scattering was used to verify liquid crystalline phases, revealing that the silsesquioxane-based derivatives formed hexagonal columnar and nematic mesophases, and the effect of the molecular structure of the mesogens and the spacer length on the formation of LC phases is discussed. This investigation demonstrated that the choice of the "side-on" attachments plays a crucial role in enhancing the emergence of the nematic phase.

Bimetallic liquid crystal blends based on structurally related 3d-metal coordination complexes.

Hetero-bimetallic liquid crystalline materials, exhibiting a single Colhex mesophase, were obtained by simple chemical blending between two structurally-related Cu(II) and Zn(II) metallomesogens based on 1,10-phenanthroline and two chelating gallate ligands. Mesomorphous and optical properties were modified upon their relative respective proportions. This study highlights the numerous possibilities for the fabrication of new multifunctional polymetallic materials, with the possibility of tuning the properties and controlling supramolecular interactions between metal centres and corresponding synergistic effects.

Induction and Stabilization of Columnar Mesophases in Fluorinated Polycyclic Aromatic Hydrocarbons by Arene-Perfluoroarene Interactions.

The straightforward synthesis of several Fluorinated Polycyclic Aromatic Hydrocarbons by the efficient, transition-metal-free, arene fluorine nucleophilic substitution reaction is described, and the full investigation of their liquid crystalline and optical properties reported. The key precursors for this study, i. e. 2,2'-dilithio-4,4',5,5'-tetraalkoxy-1,1'-biphenyl derivatives, were obtained in two steps from the highly selective Scholl oxidative homo-coupling of 3,4-dialkoxy-1-bromobenzene, followed by quantitative double-lithiation. In situ room temperature nucleophilic annulation with either perfluorobenzene or perfluoronaphthalene leads to 1,2,3,4-tetrafluoro-6,7,10,11-tetraalkxoytriphenylenes and 9,10,11,12,13,14-hexafluoro-2,3,6,7-tetraalkoxybenzo[f]tetraphenes, respectively, in good yields. Exploiting the same strategy, subsequent double annulations resulted in the formation of 9,18-difluoro-2,3,6,7,11,12,15,16-octa(alkoxy)tribenzo[f,k,m]tetraphenes and 9,10,19,20-tetrafluoro-2,3,6,7,12,13,16,17-octakis(hexyloxy)tetrabenzo[a,c,j,l]tetracenes, respectively. Despite the presence of only four alkoxy chains, the polar "Janus" mesogens display a columnar hexagonal mesophase over broad temperature ranges, with higher mesophase stability than the archetypical 2,3,6,7,10,11-hexa(alkoxy)triphenylenes and their hydrogenated counterparts. The improvement or induction of mesomorphism is attributed to efficient antiparallel face-to-face π-stacking driven by the establishment of non-covalent perfluoroarene-arene intermolecular interactions. The larger lipophilic discotic π-extended compounds also exhibit columnar mesomorphism, over similar temperature ranges and stability than their hydrogenated homologs. Finally, these fluorinated molecules form stringy gels in various solvents, and show interesting solvatochromic emission properties in solution as well as strong emission in thin films and gels.

Pyrene-Fused Poly-Aromatic Regioisomers: Synthesis, Columnar Mesomorphism, and Optical Properties.

π-Extended pyrene compounds possess remarkable luminescent and semiconducting properties and are being intensively investigated as electroluminescent materials for potential uses in organic light-emitting diodes, transistors, and solar cells. Here, the synthesis of two sets of pyrene-containing π-conjugated polyaromatic regioisomers, namely 2,3,10,11,14,15,20,21-octaalkyloxypentabenzo[a,c,m,o,rst]pentaphene (BBPn) and 2,3,6,7,13,14,17,18-octaalkyloxydibenzo[j,tuv]phenanthro [9,10-b]picene (DBPn), is reported. They were obtained using the Suzuki-Miyaura cross-coupling in tandem with Scholl oxidative cyclodehydrogenation reactions from the easily accessible precursors 1,8- and 1,6-dibromopyrene, respectively. Both sets of compounds, equipped with eight peripheral aliphatic chains, self-assemble into a single hexagonal columnar mesophase, with one short-chain BBPn homolog also exhibiting another columnar mesophase at a lower temperature, with a rectangular symmetry; BBPn isomers also possess wider mesophase ranges and higher mesophases' stability than their DBPn homologs. These polycyclic aromatic hydrocarbons all show a strong tendency of face-on orientation on the substrate and could be controlled to edge-on alignment through mechanical shearing of interest for their implementation in photoelectronic devices. In addition, both series BBPn and DBPn display green-yellow luminescence, with high fluorescence quantum yields, around 30%. In particular, BBPn exhibit a blue shift phenomenon in both absorption and emission with respect to their DBPn isomers. DFT results were in good agreement with the optical properties and with the stability ranges of the mesophases by confirming the higher divergence from the flatness of DBPn compared with BBPn. Based on these interesting properties, these isomers could be potentially applied not only in the field of fluorescent dyes but also in the field of organic photoelectric semiconductor materials as electron transport materials.

Design of Nanostructured Hybrid Electrodes Based on a Liquid Crystalline Zn(II) Coordination Complex-Carbon Nanotubes Composition for the Specific Electrochemical Sensing of Uric Acid.

A metallomesogen based on an Zn(II) coordination complex was employed as precursor to obtain a complex matrix nanoplatform for the fabrication of a high-performance electrochemical hybrid sensor. Three representative paste electrodes, which differ by the weight ratio between Zn(II) metallomesogen and carbon nanotubes (CNT), i.e., PE_01, PE_02 and PE_03, were obtained by mixing the materials in different amounts. The composition with the largest amount of CNT with respect to Zn complex, i.e., PE_03, gives the best electrochemical signal for uric acid detection by cyclic voltammetry in an alkaline medium. The amphiphilic structure of the Zn(II) coordination complex likely induces a regular separation between the metal centers favoring the redox system through their reduction, followed by stripping, and is characterized by enhanced electrocatalytic activity towards uric acid oxidation. The comparative detection of uric acid between the PE_03 paste electrode and the commercial zinc electrode demonstrated the superiority of the former, and its great potential for the development of advanced electrochemical detection of uric acid. Advanced electrochemical techniques, such as differential-pulsed voltammetry (DPV) and square-wave voltammetry (SWV), allowed for the highly sensitive detection of uric acid in aqueous alkaline solutions. In addition, a good and fast amperometric signal for uric acid detection was achieved by multiple-pulsed amperometry, which was validated by urine analysis.

[4]Cyclo-N-alkyl-2,7-carbazoles: Influence of the Alkyl Chain Length on the Structural, Electronic, and Charge Transport Properties.

Macrocycles possessing radially oriented π-orbitals have experienced a fantastic development. However, their incorporation in organic electronic devices remains very scarce. In this work, we aim at bridging the gap between organic electronics and nanorings by reporting the first detailed structure-properties-device performance relationship study of organic functional materials based on a nanoring system. Three [4]cyclo-N-alkyl-2,7-carbazoles bearing different alkyl chains on their nitrogen atoms have been synthesized and characterized by combined experimental and theoretical approaches. This study includes electrochemical, photophysical, thermal, and structural solid-state measurements and charge transport properties investigations. An optimized protocol of the Pt approach has been developed to synthesize the [4]cyclocarbazoles in high yield (52-64%), of great interest for further development of nanorings, especially in materials science. The charge transport properties of [4]cyclocarbazoles and model compound [8]cycloparaphenylene ([8]CPP) have been studied. Although no field effect (FE) mobility was recorded for the benchmark [8]CPP, FE mobility values of ca. 10-5 cm2·V-1·s-1 were recorded for the [4]cyclocarbazoles. The characteristics (threshold voltage VTH, subthreshold swing SS, trapping energy ΔE) recorded for the three [4]cyclocarbazoles appear to be modulated by the alkyl chain length borne by the nitrogen atoms. Remarkably, the space-charge-limited current mobilities measured for the [4]cyclocarbazoles are about 3 orders of magnitude higher than that of [8]CPP (1.37/2.78 × 10-4 cm2·V-1·s-1 for the [4]cyclocarbazoles vs 1.21 × 10-7 cm2·V-1·s-1 for [8]CPP), highlighting the strong effect of nitrogen bridges on the charge transport properties. The whole study opens the way to the use of nanorings in electronics, which is now the next step of their development.

Butterfly-like Shape Liquid Crystals Based Fused-Thiophene as Unidimensional Ambipolar Organic Semiconductors with High Mobility.

Mesomorphous butterfly-like shape molecules based on benzodithiophene, benzodithiophene-4,8-dione and cyclopentadithiophen-4-one core moieties were efficiently synthesized by the Suzuki-Miyaura coupling and Scholl oxidative cyclo-dehydrogenation reactions' tandem. Most of the butterfly molecules spontaneously self-organize into columnar hexagonal mesophase. The electron-deficient systems possess strong solvent-gelling ability but are not luminescent, whereas the electron-rich terms do not form gels but strongly emit light between 400 and 600 nm. The charge carrier mobility was also measured by time-of-flight transient photocurrent technique in the mesophases for some of the compounds. They display hole-transport performances with positive charge mobility in the 10-3  cm-2 V-1 s-1 range, consistent with the high degree of ordering and stability of the columnar superstructures. In particular, the mesogen with a benzodithiophen-4,8-dione core shows ambipolar charge carrier transport with both high electron (µe =6.6×10-3  cm-2 V-1 s-1 ) and hole (µh =4.5×10-3  cm-2 V-1 s-1 ) mobility values.

Playing with PtII and ZnII Coordination to Obtain Luminescent Metallomesogens.

Blue-green luminescent terpyridine-containing PtII and ZnII complexes are reported. Equipped with lipophilic gallate units, which act as monodentate ancillary coordinating ligands and/or as anions, they display low-temperature mesomorphic properties (lamello-columnar and hexagonal mesophases for PtII and ZnII complexes, respectively). The mesomorphic properties were investigated by polarised optical microscopy, differential scanning calorimetry, thermogravimetric analysis and X-ray scattering of bulk materials and oriented thin films. The model of self-assembly into the lamello-columnar phase of the PtII complex has been described in detail. The optical properties of the complexes were investigated in the liquid and condensed liquid crystalline states, highlighting the delicate balance between the role of the metal in determining the type of excited state responsible for the emission, and the role of the ancillary ligand in driving intermolecular interactions for proper mesophase formation.

Plasmonic Elastic Capsules as Colorimetric Reversible pH-Microsensors.

There is a crucial need for effective and easily dispersible colloidal microsensors able to detect local pH changes before irreversible damages caused by demineralization, corrosion, or biofilms occur. One class of such microsensors is based on molecular dyes encapsulated or dispersed either in polymer matrices or in liquid systems exhibiting different colors upon pH variations. They are efficient but often rely on sophisticated and costly syntheses, and present significant risks of leakage and photobleaching damages, which is detrimental for mainstream applications. Another approach consists of exploiting the distance-dependent plasmonic properties of metallic nanoparticles. Still, assembling nanoparticles into dispersible colloidal pH-sensitive sensors remains a challenge. Here, it is shown how to combine optically active plasmonic gold nanoparticles and pH-responsive thin shells into "plasmocapsules." Upon pH change, plasmocapsules swell or shrink. Concomitantly, the distance between the gold nanoparticles embedded in the polymeric matrix varies, resulting in an unambiguous color change. Billions of micron-size sensors can thus be easily fabricated. They are nonintrusive, reusable, and sense local pH changes. Each plasmocapsule is an independent reversible microsensor over a large pH range. Finally, their potential use for the detection of bacterial growth is demonstrated, thus proving that plasmocapsules are a new class of sensing materials.

From Chains to Monolayers: Nanoparticle Assembly Driven by Smectic Topological Defects.

In this Letter, we show how advanced hierarchical structures of topological defects in the so-called smectic oily streaks can be used to sequentially transfer their geometrical features to gold nanospheres. We use two kinds of topological defects, 1D dislocations and 2D ribbon-like topological defects. The large trapping efficiency of the smectic dislocation cores not only surpasses that of the elastically distorted zones around the cores but also surpasses the one of the 2D ribbon-like topological defect. This enables the formation of a large number of aligned NP chains within the dislocation cores that can be quasi-fully filled without any significant aggregation outside of the cores. When the NP concentration is large enough to entirely fill the dislocation cores, the LC confinement varies from 1D to 2D. We demonstrate that the 2D topological defect cores induce a confinement that leads to planar hexagonal networks of NPs. We then draw the phase diagram driven by NP concentration, associated with the sequential confinements induced by these two kinds of topological defects. Owing to the excellent large-scale order of these defect cores, not only the NP chains but also the NP hexagonal networks can be oriented along the desired direction, suggesting a possible new route for the creation of either 1D or 2D highly anisotropic NP networks. In addition, these results open rich perspectives based on the possible creation of coexisting NP assemblies of different kinds, localized in different confining areas of a same smectic film that would thus interact thanks to their proximity but also would interact via the surrounding soft matter matrix.

Nonlinear Phase Imaging of Gold Nanoparticles Embedded in Organic Thin Films.

The phase detection in the dynamic mode of the atomic force microscopes is a known technique for mapping nanoscale surface heterogeneities. We present here an additional functionality of this technique, which allows high-resolution imaging of embedded inorganic nanoparticles with diameter and interparticle distances of a few nanometers. The method is based on a highly nonlinear tip-sample interaction occurring markedly above the nanoparticles, giving thus a high phase contrast between zones with and without nanoparticles. A relationship between the tip-sample interaction strength and the phase signal is established in experiments and from calculations conducted with the model developed by Haviland et al. [ Soft Matter 2016 , 12 , 619 ], which is based on solving a combined equation of motion for both the cantilever and surface while taking into account the time-varying interaction forces. The nonlinear phase behavior at the origin of the subnanometer spatial resolution is found by numerical analyses to be the result of a local mechanical stiffening of the zone containing nanoparticles, which is enhanced by 2 orders of magnitude or more.

Supramolecular Arene-Ruthenium Metallacycle with Thermotropic Liquid-Crystalline Properties.

Functionalization of 1,4-di(4-pyridinyl)benzene with poly(arylester) dendrimers bearing cyanobiphenyl end-groups gives a bidentate dendromesogenic ligand (L) that exhibits thermotropic liquid-crystalline properties. Combination of the diruthenium complex [Ru2(p-cymene)2(donq)][DDS]2 (M) with L, by coordination-driven self-assembly, affords the discrete and well-defined metallacycle M2L2. Like L, this supramolecular dendritic system displays mesomorphic properties above 50 °C. Both compounds L and M2L2 show smectic phases, characterized by a multilayered organization of the multiple components.

Thermotropic Liquid-Crystalline and Light-Emitting Properties of Poly(pyridinium) Salts Containing Various Diamine Connectors and Hydrophilic Macrocounterions.

A set of poly(pyridinium) salts containing various diamine moieties, as molecular connectors, and poly(ethyleneglycol)-4-nonylphenyl-3-sulfopropyl ether, thereafter referred to as "Macroion", as the hydrophilic counterion, were prepared by metathesis reaction from the respective precursory tosylated poly(pyridinium)s in methanol. The structure of these ionic polymers was established by spectroscopy and chromatography techniques. The shape-persistent ionic poly(pyridinium) materials, inserting rigid or semi-rigid diamine spacers, display thermotropic liquid-crystalline properties from room-temperature up to their isotropization (in the temperature range around 160-200 °C). The nature of the LC phases is lamellar in both cases as identified by the combination of various complementary experimental techniques including DSC, POM and variable-temperature SAXS. The other polymers, inserting bulky or flexible spacers, only form room temperature viscous liquids. These new macromolecular systems can then be referred to as polymeric ionic liquid crystals (PILCs) and or polymeric ionic liquids (PILs). All the ionic polymers show excellent thermal stability, in the 260-330 °C temperature range as determined by TGA measurements, and a good solubility in common organic solvents as well as in water. Their optical properties were characterized in both solution and solid states by UV-Vis and photoluminescent spectroscopies. They emit blue or green light in both the states and exhibit a positive solvatochromic effect.

Nonlinear Nonacenes with a Dithienothiophene Substructure: Multifunctional Compounds that Act as Columnar Mesogens, Luminophores, π Gelators, and p-Type Semiconductors.

Board-like liquid-crystalline semiconductors based on the dithieno[3,2-b;2',3'-d]thiophene (DTT) substructure were synthesized and their thermal, self-assembly, optical, and semiconducting properties investigated. These sanidic compounds, bearing eight peripheral chains, are mesomorphic and spontaneously self-assemble into columnar hexagonal mesophases (Colhex ) over broad temperature ranges, as confirmed by polarized optical microscopy, differential scanning calorimetry, and small-angle X-ray scattering. Strong blue photoluminescence with absolute quantum yields up to 33 % were measured. These compounds also form blue-light emitting gels in various organic solvents. The fibrillar-like morphology of these gels, reminiscent of the columnar structure, and stabilized by efficient intermolecular interactions, was characterized by scanning electron microscopy. The charge carrier mobility of these π-extended mesogens was measured by time-of-flight transient photocurrent technique in the Colhex mesophase, and showed good hole-transport performance with charge carrier mobility of 10-3  cm2  V-1 s-1 .

Board-like Fused-Thiophene Liquid Crystals and their Benzene Analogs: Facile Synthesis, Self-Assembly, p-Type Semiconductivity, and Photoluminescence.

Fused-thiophene discotic liquid crystals were designed and easily synthesized by Suzuki coupling and FeCl3 oxidized tandem cyclodehydrogenation reactions, including homo- and cross-coupling reactions. The resulting hexagonal and rectangular columnar mesomorphic supramolecular structures formed were characterized by polarizing optical microscopy, differential scanning calorimetry, and small-angle X-ray scattering. The charge carrier transport properties in the mesophases of two of the synthesized fused-thiophene discogens were measured by transient photocurrent time-of-flight (TOF) technique, revealing fast hole transport values in the range of 10-3 to 10-2  cm2 V-1 s-1 , thus demonstrating potential applications in electronic devices. The luminescent sanidic mesogens, with different extended π-conjugated systems, also emit blue, green, or red light, with absolute photoluminescent quantum yields as high as 18 %.

Triphenylene-Imidazolium Salts and Their NHC Metal Complexes, Materials with Segregated Multicolumnar Mesophases.

Two imidazolium salts containing one or two pentadodecyloxytriphenylene units linked through a hexyloxy chain and Br-, [AuBr mCl4- m]-, or [PtBr mCl4- m]2- ( m = 0-3) as counterion have been prepared. Reaction of the imidazolium bromides with M2O (M = Cu, Ag), or carbene transmetalation from the silver product, leads to N-heterocyclic carbene complexes [MX(NHC)] (M = Cu, X = Br; M = Au, X = Cl, C≡CPh), [Ag(NHC)2][AgBr2], and [PtCl2(NHC)2], with NHC bearing one or two triphenylene fragments. Except for the gold derivatives and one Cu complex, the rest of them behave as liquid crystals organized in columnar mesophases (rectangular c2 mm or p2mg or hexagonal p6mm symmetries) with melting points in the range 30 to 60 °C and clearing points in the range 57-112 °C. The mesophase structures were determined by small-angle X-ray scattering. Structural studies and models point to nanosegregation of triphenylene columns and imidazolium/metal carbene moieties, separated by alkoxy chains, leading to multicolumnar systems. The compounds display emission spectra related to the triphenylene core in solution, in the mesophase, in the isotropic liquid, and in the solid state.

Liquid-Crystalline Tris[60]fullerodendrimers.

Liquid-crystalline tris[60]fullerodendrimers based on first- and second-generation poly(arylester)dendrons carrying cyanobiphenyl mesogens were synthesized for the first time by the olefin cross-metathesis reaction between type I (terminal) and type II (α,ß-unsaturated carbonyl) olefinic precursors, using a second-generation Grubbs or Hoveyda-Grubbs catalyst. The modular synthetic approach developed here also allowed the selective preparation of the [60]fullerene-free, mono[60]fullerodendrimer, and bis[60]fullerodendrimer derivatives from the appropriate precursors. As revealed by polarized optical microscopy, differential scanning calorimetry, and small-angle X-ray scattering, all of the materials displayed liquid-crystalline properties. In agreement with the nature of the dendritic building blocks, the emergence of lamellar mesophases (smectic C and/or smectic A phases), with the segregation of the various constitutive parts, was systematically observed. The small variation of the mesomorphic temperature range and of the mesophase stability suggested that the mesomorphism is essentially dominated by the dendrimer itself and is regulated by a subtle adaptive mechanism, in which the proportion of monolayering and bilayering arrangements of the multisegregated lamellar mesophases is modified in order to compensate the space requirements of each of the elementary building blocks, namely, the [60]fullerene units, the cyanobiphenyl mesogens, and the dendritic matrix.

Modulating the Physical and Electronic Properties over Positional Isomerism: The Dispirofluorene-Dihydroindacenodithiophene (DSF-IDT) Family.

We report the first studies on the intrinsic properties of a meta-substituted dihydroindacenodithienyl fragment and more generally the strong impact of positional isomerism on dihydroindacenodithiophene derivatives. The influence of the para and meta linkages has notably been highlighted not only for the electronic properties in solution (electrochemical properties, anodic polymerization, HOMO/LUMO energy levels, optical transitions, fluorescence spectra) but also on the physical properties in the solid state (molecular organization, crystallinity, and phase transitions). The positional isomerism hence appears to be a very efficient tool to drastically tune the properties of dihydroindacenodithiophene derivatives.