•Two series of organic solvent soluble indigoids were synthesized.•The soluble indigoids have their LUMO lowered by −0.13 to −0.26 eV compared to pristine insoluble indigo.•Compound (3a) has the lowest bandgap energy of 1.66 eV measured by CV.•Electron mobility for the soluble indigoids is within same order of magnitude of the pristine indigo using OFET measurement.Two new series of organic soluble indigoids 7-7′-dialkoxyindigoids (2a, 2b) and 4,4′-dibromo-7,7′-dialkoxyindigoids (3a, 3b) (alkoxy = n-butoxy and n-octyloxy) were synthesized starting from the inexpensive 3-hydroxybenzaldehyde. The indigoids were soluble in common organic solvents including chloroform, dichloromethane, toluene, ethyl acetate and ethers. The enhanced solubility was suggested to be a lack of intermolecular hydrogen-bonds as confirmed by single crystal X-ray diffraction analyses. It was found that intramolecular hydrogen-bonds in indigoids are crucial to the exhibition of field-effect in OFETs, while intermolecular hydrogen-bonds only caused insolubility of the indigoids. Compared to the pristine insoluble indigo (LUMO = −3.55 eV and Eg = 1.91 eV), the soluble indigoids containing electron donating alkoxy side chains at the indigoid 7 and 7′ positions were shown to have their LUMO decreased by −0.13 to −0.26 eV. Among the indigoid studied, the soluble indigoid 3a containing electron donating alkoxy side chains at the indigoid 7 and 7′ positions and bromine groups at the indigoid 4 and 4′ positions exihibited a narrowest bandgap energy with Eg = 1.66 eV. Employing the same fabrication technique and a bottom-gate-top-contact OFET configuration, the soluble indigoids were found to have electron mobility similar to and within an order of magnitude of the pristine indigo.

•Two novel blue fluorescent polymeric dyes with narrow FWHM were prepared.•The polymers are totally soluble in common organic solvents and P(3ADQ) is also soluble in aqueous mixture.•The complete amorphous polymers have excellent thermal stability.•The photoluminescence of 3MADQ and P(3ADQ) has remarkable sensitivity to pH.Two new blue fluorescent polymers, poly(9,10-di(2-naphthalenyl)-2-vinylanthracene) (P(2ADN)) and poly(9,10-di(3-quinolinyl)-2-vinylanthracene) (P(3ADQ)), were polymerized from free radical solution addition polymerization with Mn = 21,500 and 15,400, respectively. The polymers are highly soluble in common organic solvents while P(3ADQ) is also soluble in polar solvents including a 1/1 mixture of ethanol/water. Both polymers are amorphous with excellent thermal stability (Tg (Midpoint) = 343 °C and 298 °C for P(2ADN) and P(3ADQ), respectively). P(2ADN) exhibited three prominent absorption bands in tetrahydrofuran (364, 383 and 403 nm) and is similar to that of P(3ADQ) (369, 384 and 404 nm). The solid-state Commission Internationale d’Eclairage (CIEx,y) color coordinates for illumination were (0.15, 0.10) for P(2ADN) and (0.15, 0.13) for P(3ADQ) which lied within the requirements for a true blue display color. The photoluminescence (PL) of the polymers red-shifted 16–17 nm from their respective pendant chromophore 2-methyl-9,10-di(2-naphthalenyl)anthracene (2MADN) and 2-methyl-9,10-di(3-quinolinyl)anthracene (3MADQ) and can be attributed to partial π–π stacking between the adjacent aromatic pendant groups in the polymer chains. The luminescences of 3MADQ and P(3ADQ) are sensitive to pH and the pKa for the alkalescent 3MADQ and P(3ADQ) calculated was 2.4 and 2.7, respectively. Both polymers have similar band-gap energy (Eg) between 2.88 and 2.91 eV, while the LUMO/HOMO for P(3ADQ) is shifted slightly downward −0.06 to −0.03 eV compared to P(2ADN). The mobility (μhole) of the two polymers were measured to be 4.0 × 10−7 and 10−8 cm2/(V-s) for P(2ADN) and P(3ADQ), respectively.

In a homojunction device, a single organic layer assumes the multiple roles of hole, electron transportation, and emitter. Its ease in processing is highly desirable from the manufacturing point of view. In this paper, we shall describe the synthesis of a range of bipolar small molecules and conductive vinyl polymers for application in homojunction and heterojunction organic light emitting diodes (OLEDs). The bipolar materials, in general, consist of three basic building blocks: an arylamine, a 1,3,4-oxadiazole, and a polycyclic aromatic moiety. The achievement of charge balance can be validated either by direct measurement of electron/hole mobility or indirectly via optimization of device properties. A series of conductive vinyl copolymers containing hole transporting N-(4-methoxyphenyl)-N-(4-vinylphenyl)naphthalen-1-amine (4MeONPA) and electron transporting 2-phenyl-5-(4-vinylphenyl)-1,3,4-oxadiazole (OXA) at different compositions was applied for heterojunction and homojunction OLEDs. For heterojunction devices employed the copolymers as the hole transporting layer and Alq3 as the electron transporting and emitting layer, a maximum luminance and current efficiency of over 23000 cd/m2 and 4.2 cd/A (PL of Alq3), respectively, were achieved at the charge balance composition. Homojunction devices for the copolymers were demonstrated by the addition of rubrene as a dopant. The single layer devices at the optimal copolymer composition has ca 1500 cd/m2 and 0.74 cd/A.

A series of donor–acceptor type ambipolar electroluminescence dyes with the general structure PQ(OXD)nT (where n = 1, 2 and 3) were prepared, in which PQ is 2-phenylquinoline, T is diphenylamine which constituted the hole transporting triphenylamine moiety with an adjacent phenyl ring, and OXD is an electron transporting 2-phenyl-1,3,4-oxadiazole repeating unit. The compounds fluoresced bluish green to green hue in solid-state, exhibited a positive solvatochromism in solution and their quantum efficiency decreased rapidly with increase in n. The materials are thermally stable with glass transition temperature (Tg) ranging from 83 °C (n = 1) to 130 °C (n = 3). Cyclic voltammetry studies indicated the HOMO remained relatively unchanged with n while the LUMO decreased (away from the vacuum level) with an increase in the number of OXD. For single layer homojunction OLEDs, highest efficiency was obtained when n = 1 (max luminous 3300 cd/m2 and current efficiency 0.9 cd/A), whereas for multilayer heterojunction OLEDs, best results was achieved for compounds with n = 1 or 2 assuming the role of the HT layer (over 8200 cd/m2 max and 2.0 cd/A). Formation of exciplexes led to significant red-shift and lower emission efficiency for the compound with n = 3.

A series of fluorescent dyes consisted of a thiophene unit, an 1,3,4-oxadiazole unit and four different arylamine moieties were prepared using a facile multi-steps synthetic route with high yield. The four arylamine structures studied were triphenylamine, N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine, diphenyl(1-naphthyl)amine and 9-phenylcarbazole. Experimental results shown that their HOMOs varied from 5.21 to 5.73 eV strongly affected by the arylamine chemistry while their LUMOs remained relatively unchanged. Their corresponding emission colors ranged from UV (393 nm) to bluish green (483 nm). In general, the thiophene unit enhanced the overall thermal stability of the compounds. According to cyclic voltammetry, the compounds are predominantly hole-transporting while OLED results indicated cpd 10 possess both hole and electron transport properties. Single layer OLED fabricated from 10 resulted in ca. 2000 cd/m2 (luminous intensity) and 1.10 cd/A (current efficiency) max, whereas, a multilayer OLED using 10 as the hole transporting layer achieved over 7400 cd/m2 and 2.3 cd/A max.

Poly(phenyl vinyl sulfoxide) (PVSO) is a soluble precursor to polyacetylene (PA). Upon thermal elimination, the thermally labile PVSO can be converted to PA by undergoing a ‘zipper-like’ 5-members cyclic sigmatropic elimination process. Both PVSO and its copolymers can be synthesized via anionic polymerization in which stereospecific polymers with controlled molecular weight, narrow polydispersity, and known chemical composition distribution can be prepared. The degree of elimination and thus the mean conjugation length can be controlled by partially oxidizing the thermally labile sulfoxide moieties into thermally stable sulfone moieties. The optical properties of the PVSO copolymers in the UV–vis range were studied as a function of its thermolysis conditions both in solid-state and in solution forms. The eliminated PVSO can be doped (by p- or n-type dopants) to achieve conductivity to a range of 10 S/cm. The electrical properties of the PVSO copolymers and a series of blends were analyzed as a function of its chemical composition. In addition, the anionic synthesis method allows specific end groups to be inserted to the polymer chain ends. The synthesis of a series of carboxylic acid terminated PVSO polymers and their properties was also reported.

The optimum composition and film thickness determined for a single-layer organic light emitting diodes (120–150 cd/m2 at 30 mA/cm2) has been determined in one of our previous publication [Display 21 (2001) 199]. In this following study, a series of additives was included in the original composition for the purposes of color tuning, enhancement of the device efficiency as well as the stability of the polymer thick film-organic light emitting diodes (PTF-OLED). The additives attempted including three dyes (rubrene, perylene and DCM), three sensitizers (naphthalene, anthracene and p-terphenyl), several stabilizers (antioxidant and photo-stabilizer) and a number of organic soluble salts known as phase transfer catalyst. Rubrene was found being able to improve the OLED efficiency by 3-fold and its durability by at least 60 times at a concentration of 5–10 pph (in part per hundred of Alq3 replaced). The color of the OLED can also be tuned according to the additional dye used. The sensitizer naphtahlene can also improved the efficiency of the OLED by 2-fold while the effect of the other additives was less significant. In addition, the lowering of the turn-on voltage and thus a higher current efficiency resulted by the addition of a charge injection layer (lithium fluoride or calcium fluoride) in between the cathode and the organic layer. The performance of the doped PTF-OLED is within an order of magnitude compared to a heterojunction small molecule-based OLED.

Poly(phenyl vinyl sulfoxide) which is a soluble precursor to polyacetylene can be prepared using the ‘living’ anionic synthesis method. The thermal labile sulfoxide moieties can be readily converted to acetylenic units upon heating. In this report, a series of monodisperse end-functionalized soluble precursors were prepared. Details on the synthesis and characterization procedures were described. The end groups were either Li, Na, or Cs salts of carboxylic acid and were the result of using the respective electron-transfer di-functional metal naphthalide initiator. The IR spectra for the resulting telechelic polyacetylene are also given.

A guest–host approach was used to fabricate a one-layer organic light emitting diode (OLED). The thick film ink approach allows the two-dimensional OLED to be processed using traditional methods such as silk-screen printing. The I–V–L characteristics of the polymer thick film (PTF)-OLED were studied as a function of the device chemical compositions and physical configurations. Different polymers, hole and electron transporters, and emitters at different weight ratios were studied for its composition dependence. Device configuration also plays a significant role on its overall performance. Dependence on film thickness, electrode type, and the usage of additional charge injection layers were also investigated. The simplified one-layer device allows a straightforward interpretation for the charge-transport and recombination phenomena which shed light for its future improvement.