Ion‐Pairing Assemblies of Porphyrin–AuIII Complexes in Combination with π‐Electronic Receptor–Anion Complexes

Anion complexes of anion‐responsive π‐electronic molecules can behave as pseudo π‐electronic anions providing various ion pairs in combination with countercations. In this study, single crystals of ion‐pairing assemblies comprising porphyrin–Au^III complexes and Cl^? complexes of dipyrrolyldiketone BF₂ complexes were prepared from 1:1 mixtures of anion receptors and the Cl^? salts of cationic porphyrins in solution. In the solid state, the ion pairs formed characteristic assemblies, depending on the substituents of the anion receptors and porphyrin–Au^III complexes. Theoretical calculations on the ion pairs revealed that the stacking structures are stabilized by compensating positive and negative charges as well as π–π interactions.     

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 %.     

π‐Electron Systems That Form Planar and Interlocked Anion Complexes and Their Ion‐Pairing Assemblies

Interactions between designed charged species are important for the ordered arrangements of π‐electron systems in assembled structures. As precursors of π‐electron anion units, new arylethynyl‐substituted dipyrrolyldiketone boron complexes, which showed anion‐responsive behavior, were synthesized. They formed a variety of receptor–anion complexes ([1+1] and [2+1] types) in solution, and the stabilities of these complexes were discussed in terms of their thermodynamic parameters. Solid‐state ion‐pairing assemblies of [1+1]‐ and [2+1]‐type complexes with countercations were also revealed by single‐crystal X‐ray analysis. In particular, a totally charge‐segregated assembly was constructed based on negatively and positively charged layers fabricated from [2+1]‐type receptor–anion complexes and tetrabutylammonium cations, respectively. Furthermore, the [1+1]‐type anion complex of the receptor possessing long alkyl chains exhibited mesophases based on columnar assembled structures with contributions from charge‐by‐charge and charge‐segregated arrangements, which exhibited charge‐carrier transporting properties.     

Ion‐Free and Ion‐Pairing Assemblies of Anion‐Responsive π‐Electronic Systems Possessing Directly Linked Alkyl Chains

Alkyl‐substituted pyrrole‐based anion‐responsive π‐electronic systems formed supramolecular gels and liquid crystals through effective π–π stacking and van der Waals interactions. The addition of chloride as a planar cation salt afforded ion‐pairing assemblies as soft materials comprising planar receptor‐Cl^? complexes and the cation.     

Toward Ultralow‐Bandgap Liquid Crystalline Semiconductors: Use of Triply Fused Metalloporphyrin Trimer–Pentamer as Extra‐large π‐Extended Mesogenic Motifs

In contrast with their dimeric homologue, triply fused zinc porphyrin trimer–pentamer, as extra‐large π‐extended mesogens, assemble into columnar liquid crystals (LCs) when combined with 3,4,5‐tri(dodecyloxy)phenyl side groups ( 3 P_Zn – 5 P_Zn , Figure 1 ). Their LC mesophases develop over a wide temperature range, namely, 41–280 °C (on heating) for 5 P_Zn , and all adopt an oblique columnar geometry, typically seen in columnar LC materials involving strong mesogenic interactions. These LC materials are characterized by their wide light‐absorption windows from the entire visible region up to a near infrared (NIR) region. Such ultralow‐bandgap LC materials are chemically stable and serve as hole transporters, in which 5 P_Zn gives the largest charge carrier mobility (2.4×10^?2 cm V^?1 s^?1) among the series. Despite a big dimensional difference, they coassemble without phase separation, in which the resultant LC materials display essentially no deterioration of the intrinsic conducting properties.     

Corannulene‐Fused Anion‐Responsive π‐Conjugated Molecules that Form Self‐Assemblies with Unique Electronic Properties

The fusion of bowl‐shaped π‐conjugated corannulene units to anion‐responsive π‐conjugated dipyrrolyldiketone‐boron complexes resulted in new molecular materials with a unique self‐assembly capability. The bowl‐fused receptor with aliphatic tails could form both supramolecular gels and mesophases through π‐stacking interactions and also exhibited anion‐responsive characteristics. The presence of the π‐bowl unit not only afforded enhanced self‐assembly capability both in solution and in the mesophases, as evidenced by gelation experiments and phase‐transition profiles, but also enhanced intrinsic charge‐carrier mobility.     

Structural Polymorphism and Thin Film Transistor Behavior in the Fullerene Framework Molecule 5,6;11,12‐di‐o‐Phenylenetetracene

The molecular structure of the hydrocarbon 5,6;11,12‐di‐o‐phenylenetetracene (DOPT), its material characterization and evaluation of electronic properties is reported for the first time. A single‐crystal X‐ray study reveals two different motifs of intramolecular overlap with herringbone‐type arrangement displaying either face‐to‐edge or co‐facial face‐to‐face packing depicting intensive π–π interactions. Density functional theory (DFT) calculations underpin that a favorable electronic transport mechanism occurs by a charge hopping process due to a π‐bond overlap in the DOPT polymorph with co‐facial arene orientation. The performance of polycrystalline DOPT films as active organic semiconducting layer in a state‐of‐the‐art organic field effect transistor (OFET) device was evaluated and proves to be film thickness dependent. For 40 nm layer thickness it displays a saturation hole mobility (μ_hole) of up to 0.01 cm² V^?1 s^?1 and an on/off‐ratio (I_on/I_off) of 1.5×10³.     

Dithieno[3,2‐b:2′,3′‐d]pyrrole Cored p‐Type Semiconductors Enabling 20 % Efficiency Dopant‐Free Perovskite Solar Cells

Organic p‐type semiconductors with tunable structures offer great opportunities for hybrid perovskite solar cells (PVSCs). We report herein two dithieno[3,2‐b:2′,3′‐d]pyrrole (DTP) cored molecular semiconductors prepared through π‐conjugation extension and an N‐alkylation strategy. The as‐prepared conjugated molecules exhibit a highest occupied molecular orbital (HOMO) level of ?4.82 eV and a hole mobility up to 2.16×10^?4 cm² V^?1 s^?1. Together with excellent film‐forming and over 99 % photoluminescence quenching efficiency on perovskite, the DTP based semiconductors work efficiently as hole‐transporting materials (HTMs) for n‐i‐p structured PVSCs. Their dopant‐free MA_0.7FA_0.3PbI_2.85Br_0.15 devices exhibit a power conversion efficiency over 20 %, representing one of the highest values for un‐doped molecular HTMs based PVSCs. This work demonstrates the great potential of using a DTP core in designing efficient semiconductors for dopant‐free PVSCs.     

Benzodifuran‐containing well‐defined π‐conjugated polymers for photovoltaic cells

Two well‐defined alternating π‐conjugated polymers containing a soluble electroactive benzo[1,2‐b:4,5‐b′]difuran (BDF) chromophore, poly(BDF‐(9‐phenylcarbazole)) (PBDFC), and poly(BDF‐benzothiadiazole) (PBDFBTD) were synthesized via Sonogashira copolymerizations. Their optical, electrochemical, and field‐effect charge transport properties were characterized and compared with those of the corresponding homopolymer PBDF and random copolymers of the same overall composition. All these polymers cover broad optical absorption ranges from 250 to 750 nm with narrow optical band gaps of 1.78–2.35 eV. Both PBDF and PBDFBTD show ambipolar redox properties with HOMO levels of ?5.38 and ?5.09 eV, respectively. The field‐effect mobility of holes varies from 2.9 × 10^?8 cm² V^?1 s^?1 in PBDF to 1.0 × 10^?5 cm² V^?1 s^?1 in PBDFBTD. Bulk heterojunction solar cell devices were fabricated using the polymers as the electron donor and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester as the electron acceptor, leading to power conversion efficiencies of 0.24–0.57% under air mass 1.5 illumination (100 mW cm^?2). These results indicate that their band gaps, molecular electronic energy levels, charge mobilities, and molecular weights are readily tuned by copolymerizing the BDF core with different π‐conjugated units. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

The Role of Torsional Dynamics on Hole and Exciton Stabilization in π‐Stacked Assemblies: Design of Rigid Torsionomers of a Cofacial Bifluorene

Exciton and charge delocalization across π‐stacked assemblies is of importance in biological systems and functional polymeric materials. To examine the requirements for exciton and hole stabilization, cofacial bifluorene ( F 2) torsionomers were designed, synthesized, and characterized: unhindered (model) ^Me F 2, sterically hindered ^tBu F 2, and cyclophane‐like ^C F 2, where fluorenes are locked in a perfect sandwich orientation via two methylene linkers. This set of bichromophores with varied torsional rigidity and orbital overlap shows that exciton stabilization requires a perfect sandwich‐like arrangement, as seen by strong excimeric‐like emission only in ^C F 2 and ^Me F 2. In contrast, hole delocalization is less geometrically restrictive and occurs even in sterically hindered ^tBu F 2, as judged by 160 mV hole stabilization and a near‐IR band in the spectrum of its cation radical. These findings underscore the diverse requirements for charge and energy delocalization across π‐stacked assemblies.     

Steric Control in the π‐Dimerization of Oligothiophene Radical Cations Annelated with Bicyclo[2.2.2]octene Units

A Two series of oligothiophenes 2 (nT) (n=4,5), annelated with bicyclo[2.2.2]octene (BCO) units at both ends, and quaterthiophenes 3 a – c , annelated with various numbers of BCO units at different positions, were newly synthesized to investigate the driving forces of π‐dimerization and the structure–property relationships of the π‐dimers of oligothiophene radical cations. Their radical‐cation salts were prepared through chemical one‐electron oxidation by using nitrosonium hexafluoroantimonate. From variable‐temperature electron spin resonance and electronic absorption measurements, the π‐dimerization capability was found to vary among the members of the 2 (nT)^{+ .} SbF₆^? series and 3 ^{+ .} SbF₆^? series of compounds. To examine these results, density functional theory (DFT) calculations at the M06‐2X/6‐31G(d) level were conducted for the π‐dimers. This level of theory was found to successfully reproduce the previously reported X‐ray structure of ( 2 (3T))₂²⁺ having a bent π‐dimer structure with cis–cis conformations. The absorption bands obtained by time‐dependent DFT calculations for the π‐dimers were in reasonable agreement with the experimental spectra. The attractive and repulsive forces for the π‐dimerization were divided into four factors: 1) SOMO–SOMO interactions, 2) van der Waals forces, 3) solvation, and 4) Coulomb repulsion, and the effects of each factor on the structural differences and chain‐length dependence are discussed in detail.     

Formation of an Isolable Divinylborinium Ion through Twofold 1,2‐Carboboration between a Diarylborinium Ion and Diphenylacetylene

Borinium ions, that is, two‐coordinate boron cations, are the most electron‐deficient isolable boron compounds. As borinium ions have only four formal valence electrons on boron, they should show a strong tendency to accept electron pairs on the boron atom to fill its valence shell. Thus chemical reactions of borinium ions are expected to give products in which the coordination number of boron is increased from two to three or four. However, contrary to this expectation, we found that the dimesitylborinium ion (Mes₂B⁺) undergoes twofold 1,2‐carboboration reactions with two equivalents of diphenylacetylene to yield an unprecedented borinium ion ( 1 ⁺) with two substituted vinyl groups on the boron center. NMR spectroscopy and X‐ray diffraction analysis of 1 ⁺, together with electronic‐structure calculations, revealed that the positive charge is delocalized over the entire π‐conjugated system. The fact that the chemical transformation of a borinium ion gives rise to a different borinium ion without a change in the coordination number is remarkable and should provide new insight into the chemistry of the Group 13 elements.     

Induced‐Fit Binding of π‐Electron‐Donor Substrates to Macrocyclic Aromatic Ether Imide Sulfones: A Versatile Approach to Molecular Assembly

Novel macrocyclic receptors that bind electron‐donor aromatic substrates through π‐stacking donor–acceptor interactions are obtained by cycloimidisation of an amine‐functionalised aryl ether sulfone with pyromellitic and 1,4,5,8‐naphthalenetetracarboxylic dianhydrides. These macrocycles can form complexes with a wide variety of π‐donor substrates, including tetrathiafulvalene, naphthalene, anthracene, pyrene, perylene and functional derivatives of these polycyclic hydrocarbons. The resulting supramolecular assemblies range from simple 1:1 complexes to [2]‐ and [3]pseudorotaxanes and even (as a result of crystallographic disorder) an apparent polyrotaxane. Direct five‐component self‐assembly of a metal‐centred [3]pseudorotaxane is also observed on complexation of a macrocyclic ether imide with 8‐hydroxyquinoline in the presence of palladium(II) ions. Binding studies in solution were carried out by using ¹H NMR and UV/Vis spectroscopy, and the stoichiometries of binding were confirmed by Job plots based on the charge‐transfer absorption bands. The highest association constants were found for strong π‐donor guests with large surface areas, notably perylene and 1‐hydroxypyrene, for which K_a values of 1.4×10³ and 2.3×10³ M ^?1, respectively, were found. Single‐crystal X‐ray analyses of the receptors and their derived complexes reveal large induced‐fit distortions of the macrocyclic frameworks as a result of complexation. These structures provide compelling evidence for the existence of strong attractive forces between the electronically complementary aromatic π systems of host and guest.     

2,3,4,5‐Tetrakis­[(2‐hydroxy­ethyl)­thio]­tetra­thia­fulvalene tetra­fluoro­borate

The title complex, C₁₄H₂₀O₄S₈^+.BF₄^?, is a charge‐transfer complex with typical charges for the donor and anion of +1 and ?1, respectively. Two centrosymmetrically related donors form a face‐to‐face π‐dimer with a strong intermolecular S?S interaction. These π‐dimers stack along the a axis to form a donor column. The structure is extensively hydrogen bonded.     

Two rhod­amine derivatives: 9‐[2‐(ethoxycarbonyl)phenyl]‐3,6‐bis(ethyl­amino)‐2,7‐di­methyl­xanthyl­ium chloride monohydrate and 3,6‐di­amino‐9‐[2‐(methoxy­carbonyl)­phenyl]xanthyl­ium chloride trihydrate

The title compounds, C₂₈H₃₁N₂O₃⁺·Cl^?·H₂O (common name rhod­amine‐6g), (I), and C₂₁H₁₇N₂O₃⁺·Cl^?·3H₂O (common name rhod­amine‐123), (II), both have planar xanthene skeletons with a formal +1 charge on the amino N atoms delocalized through the π‐electron system so that the N—Csp² bond distances indicate significant double‐bond character. The substituted planar phenyl groups make angles of 63.29 (8) and 87.96 (11)° with the xanthene planes in (I) and (II), respectively. In both mol­ecules, the carbonyl bond vectors point toward the xanthene rings. The ethyl­amine groups in (I) are oriented similarly with their CH₂–CH₃ bond vectors pointing nearly perpendicular to the xanthene plane. The chloride ions and water mol­ecules are disordered in both structures. In (I), the chloride ion and water mol­ecule are disordered between two sites. One water and chloride alternately occupy the same site with occupancy factors of 0.5. The other 0.5‐chloride and 0.5‐water occupy two distinct positions separated by 0.747 (8) Å. In (II), the chloride ion is disordered between three sites and one of the waters is disordered about two other sites. Both crystal structures are stabilized by hydrogen bonds involving the chloride ions, amino groups and water mol­ecules, as well as by π–π stacking between xanthene planes.     

Hydrogen‐bonded assemblies in the molecular crystals of 2,2′‐thiodiacetic acid with ethylenediamine and o‐phenylenediamine

Carboxylate molecular crystals have been of interest due to the presence of hydrogen bonding, which plays a significant role in chemical and crystal engineering, as well as in supramolecular chemistry. Acid–base adducts possess hydrogen bonds which increase the thermal and mechanical stability of the crystal. 2,2′‐Thiodiacetic acid (Tda) is a versatile ligand that has been widely explored, employing its multidendate and chelating coordination abilities with many metals; however, charge‐transfer complexes of thiodiacetic acid have not been reported. Two salts, namely ethylenediaminium 2,2′‐thiodiacetate, C₂H₁₀N₂²⁺·C₄H₄O₄S₂²⁻, denoted Tdaen, and 2‐aminoanilinium 2‐(carboxymethylsulfanyl)acetate, C₆H₉N₂⁺·C₄H₅O₄S⁻, denoted Tdaophen, were synthesized and characterized by IR, ¹H and ¹³C NMR spectroscopies, and single‐crystal X‐ray diffraction. In these salts, Tda reacts with the aliphatic (ethylenediamine) and aromatic (o‐phenylenediamine) diamines, and deprotonates them to form anions with different valencies and different supramolecular networks. In Tdaen, the divalent Tda²⁻ anions form one‐dimensional linear supramolecular chains and these are extended into a three‐dimensional sandwich‐type supramolecular network by interaction with the ethylenediaminium cations. However, in Tdaophen, the monovalent Tda⁻ anions form one‐dimensional zigzag supramolecular chains, which are extended into a three‐dimensional supramolecular network by interaction with the 2‐aminoanilinium cations. Thus, both three‐dimensional structures display different ring motifs. The structures of these diamines, which are influenced by hydrogen‐bonded assemblies in the molecular crystals, are discussed in detail.     

Thienoacene‐Fused Pentalenes: Syntheses,Structures, Physical Properties and Applications for Organic Field‐Effect Transistors

Three soluble and stable thienoacene‐fused pentalene derivatives ( 1 – 3 ) with different π‐conjugation lengths were synthesized. X‐ray crystallographic analysis and density functional theory (DFT) calculations revealed their unique geometric and electronic structures due to the interaction between the aromatic thienoacene units and antiaromatic pentalene moiety. As a result, they all possess a small energy gap and show amphoteric redox behaviour. Time dependent (TD) DFT calculations were used to explain their unique electronic absorption spectra. These new compounds exhibited good thermal stability and ordered packing in solid state and thus their applications in organic field‐effect transistors (OFETs) were also investigated. The highest field‐effect hole mobility of 0.016, 0.036 and 0.001 cm² V^?1 s^?1 was achieved for solution‐processed thin films of 1 – 3 , respectively.     

N‐Annulated Perylene‐Substituted and Fused Porphyrin Dimers with Intense Near‐Infrared One‐Photon and Two‐Photon Absorption

Fusion of two N‐annulated perylene (NP) units with a fused porphyrin dimer along the S₀–S₁ electronic transition moment axis has resulted in new near‐infrared (NIR) dyes 1 a / 1 b with very intense absorption (ε>1.3×10⁵ M ^?1 cm^?1) beyond 1250 nm. Both compounds displayed moderate NIR fluorescence with fluorescence quantum yields of 4.4×10^?6 and 6.0×10^?6 for 1 a and 1 b , respectively. The NP‐substituted porphyrin dimers 2 a / 2 b have also been obtained by controlled oxidative coupling and cyclodehydrogenation, and they showed superimposed absorptions of the fused porphyrin dimer and the NP chromophore. The excited‐state dynamics of all of these compounds have been studied by femtosecond transient absorption measurements, which revealed porphyrin dimer‐like behaviour. These new chromophores also exhibited good nonlinear optical susceptibility with large two‐photon absorption cross‐sections in the NIR region due to extended π‐conjugation. Time‐dependent density functional theory calculations have been performed to aid our understanding of their electronic structures and absorption spectra.     

Synthesis and photovoltaic investigation of dithieno[2,3‐d:2′,3′‐d′]‐benzo[1,2‐b:3,4‐b′:5,6‐d″]trithiophene‐based conjugated polymer with an enlarged π‐conjugated system

Compared with benzo[1,2‐b:3,4‐b′:5,6‐d″]trithiophene (BTT), an extended π‐conjugation fused ring derivative, dithieno[2,3‐d:2′,3′‐d′]benzo[1,2‐b:3,4‐b′:5,6‐d″]trithiophene (DTBTT) has been designed and synthesized successfully. For investigating the effect of extending conjugation, two wide‐bandgap (WBG) benzo[1,2‐b:4,5‐b′]dithiophene (BDT)‐based conjugated polymers (CPs), PBDT‐DTBTT, and PBDT‐BTT, which were coupled between alkylthienyl‐substituted benzo[1,2‐b:4,5‐b′]dithiophene bistin (BDT‐TSn) and the weaker electron‐deficient dibromides DTBTTBr₂ and BTTBr₂ bearing alkylacyl group, were prepared. The comparison result revealed that the extending of conjugated length and enlarging of conjugated planarity in DTBTT unit endowed the polymer with a wider and stronger absorption, more ordered molecular structure, more planar and larger molecular configuration, and thus higher hole mobility in spite of raised highest occupied molecular orbital (HOMO) energy level. The best photovoltaic devices exhibited that PBDT‐DTBTT/PC₇₁BM showed the power conversion efficiency (PCE) of 2.73% with an open‐circuit voltage (V_OC) of 0.82 V, short‐circuit current density (J_SC) of 6.29 mA cm^?2, and fill factor (FF) of 52.45%, whereas control PBDT‐BTT/PC₇₁BM exhibited a PCE of 1.98% under the same experimental conditions. The 38% enhanced PCE was mainly benefited from improved absorption, and enhanced hole mobility after the conjugated system was extended from BTT to DTBTT. Therefore, our results demonstrated that extending the π‐conjugated system of donor polymer backbone was an effective strategy of tuning optical electronic property and promoting the photovoltaic property in design of WBG donor materials.     

Reverse Arene Sandwich Structures Based upon π‐Hole⋅⋅⋅[MII] (d8 M=Pt,Pd) Interactions,where Positively Charged Metal Centers Play the Role of a Nucleophile

The complexes [Pt(tpp)] (H₂tpp=tetraphenylporphyrin), [M(acac)₂] (M=Pd, Pt, Hacac=acetylacetone), and [Pd(ba)₂] (Hba=benzoylacetone) were co‐crystallized with highly electron‐deficient arene systems to form reverse arene sandwich structures built by π‐hole???[M^II] (d⁸M=Pt, Pd) interactions. The adduct [Pt(tpp)]?2 C₆F₆ is monomeric, whereas the diketonate 1:1 adducts form columnar infinity 1D‐stack assembled by simultaneous action of both π‐hole???[M^II] and C???F interactions. The reverse sandwiches are based on noncovalent interactions and calculated ESP distributions indicate that in π‐hole???[M^II] contacts, [M^II] plays the role of a nucleophile.