Selective tuning of the band gap of pi-conjugated dithieno[3,2-b:2',3'-d]phospholes toward different emission colors

The systematic extension of the pi-conjugated system of strongly blue-luminescent dithieno[3,2-b:2',3'-d]phospholes has been investigated with the goal of obtaining different emission colors. Functionalization of the 2- and 6-position of the dithienophosphole scaffold with halogen substituents provided functional building blocks for subsequent cross-coupling experiments with various homo- and heteroaryls to selectively decrease the band gap of the materials. By this strategy materials with different emission colors ranging from green via yellow to orange could be obtained. This feature supports their suitability for organic light-emitting diodes with respect to an application in full-color flat-panel displays. The experimental results were nicely supported by theoretical DFT calculations providing a deeper understanding of the electronic structure in the extended materials, and also allowing for the design of future materials based on a dithienophosphole core. Furthermore, the phosphorus center in the extended molecular materials can efficiently be fine-tuned in subsequent simple chemical functionalizations. This allows for a tailoring of the optoelectronic properties of the extended dithienophospholes to suit the requirements of potential applications.     

Synthesis and unexpected reactivity of Si-H functionalized dithieno[3,2-b:2',3'-d]phospholes

[reaction: see text]. Si-H functionalized, blue light-emitting dithieno[3,2-b:2',3'-d]phospholes are accessible by reaction of an appropriate bithiophene precursor with a dichlorophosphane. Subsequent functionalization of the central phosphorus center allows for a fine-tuning of the optoelectronic properties of the material. Pt-catalyzed reaction of the Si-H functionalities with alkynes affords the hydrosilation products including a polymer by reaction with 1,7-octadiyne. By contrast, the absence of any substrate leads to the exclusive formation of a polymer via dehydrogenative homocoupling.     

Cationic dithieno[3,2-b:2',3'-d]phospholes: a new building block for luminescent, conjugated polyelectrolytes

Cationic dithieno[3,2-b:2',3'-d]phospholes are accessible very efficiently by methylation of the phosphorus center. Further functionalization with bromo substituents in 2,6-positions affords a polymerizable monomer that can be copolymerized with a difunctionalized fluorene in a Suzuki-Miyaura-type cross-coupling protocol. The monomers as well as the resulting conjugated polyelectrolyte based on the phospholium units show very intriguing photoluminescence properties, even in the solid state. [structure: see text]     

Solution and solid-state properties of highly fluorescent dithieno[3,2-b:2',3'-d]pyrrole-based oligothiophenes

Dithieno[3,2-b:2',3'-d]pyrrole-based terthiophene and quaterthiophene analogues have been prepared from N-functionalized dithieno[3,2-b:2',3'-d]pyrroles (DTPs) via Stille coupling. In order to thoroughly study the structure-function property relationships within these DTP-based oligothiophenes, an oligomer series was prepared that allows for the investigation of a number of structural effects including chain length, thiophene functionalization, and pyrrole N-functionalization. As pyrrole N-functionalization allows the incorporation of solubilizing side chains without the unwanted steric interactions that typically reduce backbone planarity, the effect of the bulk of these side chains on the optical properties in both solution and the solid state has been carefully investigated. The DTP-based quaterthiophene, N-tert-butyl-2,6-bis(2'-thienyl)dithieno[3,2-b:2',3'-d]pyrrole was characterized via X-ray crystallography and was found to crystallize in the monoclinic space group P2(1)/c with a = 17.489(4) ?, b = 7.8855(16) ?, c = 14.540(3) ?, β = 108.37(3)°, and Z = 4. The effect of side chains on the solid-state packing of the DTP-based quaterthiophenes was further investigated through X-ray diffraction of solution processed thin films. In comparison to the parent oligothiophenes, the resulting DTP-based systems exhibit enhanced fluorescence efficiencies in solution (up to 66%) and measurable solid-state emission from thin films.     

Planar beta-linked oligothiophenes based on thieno[3,2-b]thiophene and dithieno[3,2-b:2',3'-d]thiophene fused units

A series of planar beta-linked oligothiophenes based on thieno[3,2-b]thiophene and dithieno[3,2-b:2',3'-d]thiophene fused units were synthesized. The optical data indicate a blue shift of the absorption maximum in comparison to the alpha-linked analogues due to cross-conjugation between fused rings. The crystal structures of 3,3'-bi(thieno[3,2-b]thiophene) and 3,3';6',3"-ter(thieno-[3,2-b]thiophene) reveal edge-to-face pi-stacked dimer motifs, whereas the crystal structure of 3,3'-bis(dithieno[3,2-b:2',3'-d]thiophene) consists of face-to-face pi-stacked molecules. [structure: see text]     

Synthesis and optoelectronic properties of transition metal complexes incorporating dithieno[3,2-b:2',3'-d]phosphole ligands

A series of dithieno[3,2-b:2',3'-d]phosphole-based transition metal complexes, including Au, Fe, Pt, Rh and W as central metals have been synthesised and characterised. Structural investigations by X-ray single crystal crystallography supported the high degree of pi-conjugation in the dithienophosphole ligands. This essential requirement for potential applications in molecular electronics and optoelectronics provides small band gaps for the materials. Investigations toward the optoelectronic properties of the respective complexes by fluorescence spectroscopy indicated that systematic alterations of the electronic structure are connected to different variables such as transition metal employed, functionalisation of the dithienophosphole ligands as well as complex geometries. The investigated Pt-based complexes exhibit only poor photoluminescence whereas Rh-, W- and Fe-based species with silyl functionalised dithienophosphole ligands show appreciable photophysical properties. The Au complexes investigated exhibit strong photoluminescence properties with very intriguing features in terms of excitation and emission wavelengths, intensity as well as selectivity.     

Improved synthesis of dithieno[3,2-b:2',3'-d]thiophene (DTT) and derivatives for cross coupling

An improved synthesis of dithieno[3,2-b:2',3'-d]thiophene (DTT) and its 2,6- and 3,5-dibromo derivatives has been devised; Stille cross coupling of 2,5-(bistrimethylstannyl)-DTT afforded the oligomer 12.     

Polymer solar cells based on copolymers of dithieno[3,2-b:2',3'-d]silole and thienopyrroledione

Novel low band gap copolymers based on dithienosilole and thienopyrroledione units were synthesized. Copolymer P1 with branched side chains on the TPD units demonstrated a PCE of 4.4% with a high V(oc) of 0.89 V for OPV applications while OTFT devices fabricated from a copolymer containing linear side chains (P2) performed better in OTFT device configurations.     

Dendrimeric Oligo(phenylenevinylene)‐Extended Dithieno[3,2‐b:2′,3′‐d]phospholes—Synthesis,Self‐Organization,and Optical Properties

A boost from the branches : Incorporation of the dithieno[3,2‐b:2′,3′‐d]phosphole system as a core in oligo(phenylenevinylene) dendrimers (an example is shown here) provides materials that exhibit energy‐transfer features relaying incoming photons from the dendrons towards the core, which in turn shows enhanced emission intensity. The optical properties and self‐assembly features of the dendrimers can be impacted by the terminal groups (‐H, ‐CF₃, or ‐NPh₂) employed.

     

Highly fluorescent oligothiophenes through the incorporation of central dithieno[3,2-b:2',3'-d]pyrrole units

[structures: see text] Dithieno[3,2-b:2',3'-d]pyrrole-based terthiophene (2a-c) and quaterthiophene (3a-c) analogues have been prepared from dithieno[3,2-b:2',3'-d]pyrrole (1) via Stille coupling utilizing a one-pot method. In comparison to the parent oligothiophenes (T(n), where n = 2-4), the resulting dithieno[3,2-b:2',3'-d]pyrrole-based systems exhibit enhanced fluorescence efficiencies in solution (up to 53%). These new oligomeric systems also allow the incorporation of solubilizing side chains without the negative steric interactions that typically reduce backbone planarity.     

两种非对称芳基二噻吩并[2,3-b:3',2'-d]噻吩的合成与光谱特性

合成了两种非对称芳基取代的并三噻吩化合物.以2-溴-5-三甲基硅-二噻吩并[2,3-b:3′,2′-d]噻吩为原料,经脱除四甲基硅烷(TMS)和Suzuki偶联两步反应制备了2-噻吩基二噻吩并[2,3-b:3′,2′-d]噻吩,总产率为67.4%;以2-苯基二噻吩并[2,3-b:3′,2′-d]噻吩为原料,经N-溴代琥珀酰亚胺(简称NBS)溴代和Suzuki偶联两步反应制备了2-苯-5-噻吩基二噻吩并[2,3-b:3′,2′-d]噻吩,总产率为27.8%.产物经核磁共振谱(1H NMR,13C NMR)和质谱(MS)分析确认;利用紫外-可见分光光度法(UV-Vis)分析了合成产物的荧光特性.结果表明,由于苯基的存在,2-噻吩-5-苯基二噻吩并[2,3-b:3′,2′-d]噻吩分子的共轭体系增大,导致其吸收峰红移、发光能力减弱.     

Reduced band gap dithieno[3,2-b:2',3'-d]pyrroles: new n-type organic materials via unexpected reactivity

Direct addition of tetracyanoethylene to N-(p-hexylphenyl)dithieno[3,2-b:2',3'-d]pyrrole yields not only the aromatic mono- and bis-tricyanovinyl-substituted products but also a quinoidal product with dicyanomethylene groups. The analogous reaction with dithieno[3,2-b:2',3'-d]thiophene yields exclusively the aromatic mono-tricyanovinyl product. The aromatic and quinoidal products possess red-shifted absorptions, increased electron affinities, and favorable pi-stacking motifs in comparison to the unsubstituted oligomers.     

Highly sensitive sensory materials for fluoride ions based on the dithieno[3,2-b:2',3'-d]phosphole system

[structure: see text]. The newly developed functionalization of an unsubstituted dithieno[3,2-b:2',3'-d]phosphole at the 5,5'-positions gives access to bis(pinacoleboryl) species that can be utilized as sensory materials for fluoride ions. The fluoride-triggered response of the air- and moisture-stable boryl-functionalized dithienophosphole oxide manifests itself in the generation of a new fluorescence emission that can be detected at very low analyte concentrations (ppm) or even with the naked eye upon irradiation with UV light (366 nm).     

A simple and efficient route to N-functionalized dithieno[3,2-b:2',3'-d]pyrroles: fused-ring building blocks for new conjugated polymeric systems

A general synthetic route has been developed for the simple and efficient preparation of N-functionalized dithieno[3,2-b:2',3'-d]pyrroles. These synthetic methods utilize N-functionalized N-(3'-thienyl)-3-aminothiophenes produced from the Pd-catalyzed amination of 3-bromothiophene with primary amines, followed by a one-pot bromination/cyclization process. This combination allows the convenient preparation of a variety of N-functionalized dithieno[3,2-b:2',3'-d]pyrroles (where substituent = hexyl, octyl, decyl, tert-butyl, and p-hexylphenyl) in good yield (65-82%). Characterization of the structure and reactivity of this class of compounds is also described, including electrochemical and photophysical data for all compounds and X-ray structural data for the octyl-, tert-butyl-, and p-hexylphenyl-functionalized compounds.     

Synthesis of dithieno[2,3-b:3',2'-d]thiophenes-building blocks for cross-conjugated beta-oligothiophenes

Syntheses of annelated and functionalized beta-trithiophenes (dithieno[2,3-b:3',2'-d]thiophenes), building blocks for the helically annelated, cross-conjugated beta-oligothiophenes, are reported. UV-vis spectra reveal that the effect of octyl substituents on the onset of electronic absorption in annelated beta-trithiophenes is negligible compared to the effect of helical distortion in the higher beta-oligothiophenes.     

Synthesis of dithieno[2,3-b:4',3'-d]siloles and their selective bromination

The efficient synthesis of novel unsymmetrical dithienosiloles, 7,7-dimethyl-4,6-di(trimethylsilyl)-dithieno[2,3-b:4',3'-d]silole (1) and 7,7-dimethyl-2,4,6-tri(trimethylsilyl)-dithieno[2,3-b:4',3'-d]silole (2) has been developed by intramolecular silole formation with 4,4'-dibromo-2,2',5,5'-tetrakis(trimethylsilyl)-[3,3']bithienyl (3) as the starting material in the presence of t-BuLi. Upon treatment with N-bromosuccinimide (NBS) under controlled conditions, dithieno[2,3-b:4',3'-d]silole was selectively brominated to produce mono-, di-, and tribrominated dithieno[2,3-b:4',3'-d]siloles in good yields. The crystal structures of the title compounds are described.     

Molecular tuning in highly fluorescent dithieno[3,2-b:2',3'-d]pyrrole-based oligomers: effects of N-functionalization and terminal aryl unit

A series of eight conjugated oligomers consisting of central dithieno[3,2-b:2',3'-d]pyrroles (DTPs) end-capped with either thienyl or phenyl groups have been prepared from N-alkyl-, N-aryl-, and N-acyl-dithieno[3,2-b:2',3'-d]pyrroles via Stille and Suzuki cross-coupling. The DTP-based quaterthiophene, N-phenyl-2,6-bis(2-thienyl)dithieno-[3,2-b:2',3'-d]pyrrole was characterized via X-ray crystallography and was found to crystallize in the orthorhombic space group Pna2(1) with a = 10.8666(3) ?, b = 22.8858(6) ?, c = 7.4246(2) ?, and Z = 4. The full oligomeric series was thoroughly investigated via photophysical, electrochemical, and DFT calculations in order to correlate the cumulative effects of both aryl end-groups and N-functionalization on the resulting optical and electronic properties. Through such molecular tuning, it was found to be possible to modulate the HOMO energy by as much as 0.32 V and to generate highly fluorescent oligomers with solution fluorescence efficiencies as high as 92%.