Spirobifluorene Moiety Research Articles

Morphological Stable Spirobifluorene/Oxadiazole Hybrids as Bipolar Host Materials for Efficient Green and Red Electrophosphorescence

A series of 9,9'-spirobifluorene/oxadiazole hybrids with various linkages between two components, namely SBF-p-OXD (1), SBF-m-OXD (2), and SBF-o-OXD (3) are designed and synthesized through Suzuki cross-coupling reactions. The incorporation of a rigid and bulky spirobifluorene moiety greatly improves their thermal and morphological stability, with T(d) (decomposition temperature) and T(g) (glass transition temperature) in the ranges of 401-480 degrees C and 136-210 degrees C, respectively. 2 and 3 with meta- and ortho-linkage display higher triplet energy and blue-shifted absorption and emission than their para-linked analogue 1 owing to the decreasing pi-conjugation between the two components. Their HOMO and LUMO energy levels depend on the linkage modes within the range of 5.57-5.64 eV and 2.33-2.49 eV, respectively. Multilayer deep red electrophosphorescent devices with 1-3 as hosts were fabricated and their EL efficiencies follow the order of 3 (o)>2 (m)>1 (p), which correlates with their triplet energy and the separation of HOMO and LUMO distributions at molecular orbitals. The maximum external quantum efficiencies of 11.7% for green and 9.8% for deep red phosphorescent organic light-emitting diodes (OLEDs) are achieved by using 2 and 3 as host materials, respectively.

Synthesis, Structure, and Properties of Polyacetylenes Possessing Chiral Spirobifluorene Moieties in the Side Chain

Synthesis, property, and structure of a few polyacetylenes having the pendent optically active spirobifluorene moiety as a C2 chiral group are described. Optically inactive achiral monomer 2-ethynyl-9,9′-spirobifluorene was obtained from 2-bromo-9,9′-spirobifluorene, while optically active monomers (R)-2′-ethynyl-9,9′-spirobifluorene-2-ol and (R)-2-acyloxy-2′-ethynyl-9,9′-spirobifluorene were prepared from optically pure 2,2′-dihydroxy-9,9′-spirobifluorene. Polymerizations of these monomers were carried out by a rhodium catalyst system ([Rh(nbd)Cl]2-triethylamine) in THF at room temperature to give polyacetylenes with Mw ca. 25000 in moderate yields. The chemical and thermal properties of polymers were evaluated. The structural characteristics were studied by UV-vis, CD, and Raman spectra in addition to the specific optical rotation. The experimental results suggested the formation of optically active polymers which took the cis-transoidal main chain conformation, while the main chains had helical structures as simulated (P-screwed 16-1 helix in the case of poly(R)-1-OH). The formation of one-handed helical polymers was caused by the introduction of a group with molecular chirality in the side chain.

Electrogenerated Chemiluminescence of a Spirobifluorene-Linked Bisanthracene: A Possible Simultaneous, Two-Electron Transfer

We report the electrogenerated chemiluminescence (ECL) of 2,2'-bis(10-phenylanthracen-9-yl)-9,9'-spirobifluorene (spiro-FPA), a dichromophoric molecule composed of two phenylanthracenes linked by a spirobifluorene moiety (PA-X-PA). The results are compared to those for 9,10-diphenylanthracene (DPA), a related molecule with a single chromophore. Cyclic voltammetry (CV) of spiro-FPA shows two reversible, closely spaced, one-electron transfers on both reduction and oxidation, occurring at E(o)(1,red) = -2.02, E(o)(2,red) = -2.07 V vs SCE and E(o)(1,ox) = 1.14, E(o)(2,ox) = 1.20 V vs SCE. The potentials for each pair are close enough to appear as a single peak in CV, indicating that the spirobifluorene moiety interrupts conjugation between the redox centers. The potentials observed are similar to those of DPA, which shows E(o)(red) = -2.06 V vs SCE and E(o)(ox) = 1.15 V vs SCE. The absorbance spectrum of spiro-FPA shows lambda(max,abs) = 377 nm, with 377 = 25,700 M(-1) s(-1), while DPA exhibited lambda(max,abs) = 374 nm, with 374 = 13,800 M(-1) s(-1), demonstrating that spiro-FPA has twice the available chromophores as DPA. Photoluminescence (PL) data for spiro-FPA shows lambda(max,PL) = 434 nm, with Phi(PL) = 0.74, while DPA fluoresces at 420 nm with Phi(PL) = 0.91; thus, there is greater solvent or structural relaxation in the spiro-FPA excited state, which may account for the greater internal conversion. Unlike DPA, the ECL spectrum of spiro-FPA exhibits long-wavelength emission not observed in the PL. We attribute this emission to excimers formed during annihilation ECL. Steric hindrance prevents DPA from forming excimers, even in ECL, but spiro-FPA annihilation can occur between pairs of di-ions (PA(*-)-X-PA(*-) and PA(*+)-X-PA(*+)), which are electrostatically more strongly attracted to one another than the mono-ions. This greater electrostatic attraction may be sufficient to overcome the steric hindrance to excimer formation. Lowering the electrolyte concentration decreases the electrostatic shielding of the ions from one another; thus, the increase in longer wavelength ECL accompanying a decrease in electrolyte concentration supports the role of the di-ions in excimer formation. Additionally, simulations show, consistent with experiment, a more rapid decrease in excimer concentration than in excited monomer concentration as a function of time after each potential pulse. This is probably due to the greater number of scavenging reactions available for di-ions. The simulations are confirmed experimentally when lower potential pulsing frequencies yield lower relative excimer emission. Since an excited state created by one-electron transfer between two di-ions should be rapidly quenched via electron transfer by the other PA moiety, the existence of excimers suggests the possibility of simultaneous, two-electron transfer to generate the excimer.

Luminescence properties of soluble 2,2′,7,7′‐Tetrakis(2‐(9‐hexyl‐9H‐carbazol‐3‐yl)‐vinyl)‐9,9′‐spirobifluorene‐labeled dendrimers: Photoluminescence and electroluminescence

AbstractNew light emitting dendrimers were synthesized by reacting 3,5‐bis‐(3,5‐bis‐benzyloxy‐benzyloxy)‐benzoic acid or 3,5‐bis‐[3,5‐bis‐(3,5‐bis‐benzyloxy‐benzyloxy)‐benzyloxy]‐benzoic acid with a carbazolyl vinyl spirobifluorene moiety. A blue‐emitting core dye was encapsulated by multibenzyloxy dendrons, and two dendrimers having different densities of dendrons were prepared. Photoluminescence (PL) studies of the dendrimers demonstrated that at the higher density of benzyloxy dendrons, the featureless vibronic transitions were improved, causing lesser excimer emission. The similarity of the solution and solid emission spectra of the larger dendrimer, 10, revealed the suppression of molecular aggregation in the solid film, which is attributed to the presence of the bulky benzyloxy dendrons. The electroluminescence spectra of multilayered devices made using 10 predominantly exhibited blue emissions; similar emission was observed in the PL spectra of its thin film. The multilayered devices made using 3, 9, and 10 showed luminances of 1021 cd m−2 at 5 V, 916 cd m−2 at 6 V, and 851 cd m−2 at 6.5 V, respectively. The largest dendrimer, 10, bearing a greater number of benzyloxy dendrons, exhibited a blue‐like emission with CIE 1931 chromaticity coordinates of x = 0.16 and y = 0.13, which is due to the influence of a higher shielding effect. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 501–514, 2008

Synthesis and Structure of Optically Active Polyesters Containing C2 Chiral Spirobifluorene Moieties in the Main Chain

Three optically active polyesters possessing C2 chiral spirobifluorene moieties in the main chains were prepared and their structural feature was discussed mainly by the UV-vis and CD spectral characteristics. Polycondensation of optically active (R)-(+)-2,2′-dihydroxy-9,9′-spirobifluorene 1 and terephthaloyl dichloride 2a in THF in the presence of triethylamine yielded the corresponding polyester as methanol-insoluble part (3a, 89%, Mw 5400, Mw/Mn 3.5). The polymerizations with 2,6-naphthaloyl dichloride 2b and 4,4′-azodibenzoyl dichloride 2c also afforded polyesters 3b (95%, Mw 20000, Mw/Mn 2.3) and 3c (95%, Mw 6200, Mw/Mn 2.2), respectively. In the solvent-free polymerization, the corresponding polyester 3a was obtained in 40% yield (Mw 16000). In the case of racemic 1rac, similar yield and molecular weight for 3a were achieved. Although no clear glass transition point was observed in all three polymers, these polymers had high thermal decomposition temperature over 480 °C. In the UV-vis and CD spectra of the polymers 3, bisignate Cotton effect was observed in the UV-vis absorption region of optically inactive diacid part of the repeating unit in all three polymers. Further, CD intensity of 3 depended upon temperature: the temperature increase corresponded to the decrease in CD intensity. Both the results obtained and the structure simulation of 3 suggested their helical conformation.

Solution-Processible Blue-Light-Emitting Polymers Based on Alkoxy-Substituted Poly(spirobifluorene)

Alkoxy-substituted poly(spirobifluorene)s and their copolymers with a triphenylamine derivative have been synthesized by Ni(0)-mediated polymerization. The polymers were well soluble in common organic solvents. Pure blue-light emissions without the long wavelength emission of poly(fluorene)s have been observed in the fluorescence spectra of polymer thin films. The light emitting diodes with a device configuration of ITO/PEDT:PSS(30 nm)/polymer(60 nm)/LiF(1 nm)/Al(100 nm) have been fabricated. The electroluminescence spectra showed the blue emissions without the long wavelength emission as observed in the fluorescence spectra. The relatively poor electroluminescence quantum yield of the homopolymer (0.017% @ 20 mA/cm2) with color coordinates of (0.16, 0.07) has been improved by the introduction of triphenylamine moiety, and the copolymer with triphenylamine derivative exhibited an electroluminescence quantum yield of 0.15 % at 20 mA/cm2 with color coordinates of (0.16, 0.08). Moreover, the introduction of polar side chains to the spirobifluorene moiety enhanced the device performance and led to the quantum yields of 0.6 to 0.7 % at 20 mA/cm2, although there was some expense of color purities.

Organic blue light emitting materials based on spirobifluorene

Abstract Spirobifluorene derivative, which is useful for obtaining small molecule or polymer blue light emitting materials, has been prepared. To improve the solubility of final materials, long alkoxy side chains were introduced to spirobifluorene moiety. Coupling reaction with biphenyl led to small molecule blue light emitting material. A polymer blue light emitting material was obtained through Ni(0) mediated polymerization. Using vacuum deposition and spin coating methods, small molecule and polymer light emitting devices were fabricated and their device characteristics were investigated. In this paper, the detailed preparation methods of small molecule and polymer materials, and the device characteristics will be discussed.

Synthesis and properties of soluble aromatic polyamides derived from 2,2′‐bis(4‐carboxyphenoxy)‐9,9′‐spirobifluorene

AbstractThe synthesis of a new bis(ether carboxylic acid), 2,2′‐bis(4‐carboxyphenoxy)‐9,9′‐spirobifluorene, in which two orthogonally arranged carboxyphenoxyfluorene entities are connected through an sp3 carbon atom (the spiro center), is reported. The direct phosphorylation polycondensation of this diacid monomer with various aromatic diamines yields aromatic polyamides containing 9,9′‐spirobifluorene moieties in the main chain. The presence of the spiro segment restricts the close packing of the polymer chains and decreases interchain interactions, resulting in amorphous polyamides with enhanced solubility, and high glass‐transition temperatures and good thermal stability are maintained through controlled segmental mobility. The glass‐transition temperatures of these polyamides are in the range of 234–306 °C, with 10% weight losses occurring at temperatures above 530 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1160–1166, 2003

Synthesis and characterization of soluble poly(ether imide)s based on 2,2′-bis(4-aminophenoxy)-9,9′-spirobifluorene

A series of aromatic poly(ether imide)s containing 9,9′-spirobifluorene moieties in the main chain have been synthesized via the polycondensation of 2,2′-bis(4-aminophenoxy)-9,9′-spirobifluorene with a variety of aromatic dianhydrides. In the diamine monomer, the two aminophenoxyfluorene entities are orthogonally arranged and are connected through an sp 3 carbon atom (the spiro center). The resulting poly(ether imide)s have a polymer backbone which is periodically twisted with an angle of 90° at each spiro center. This structural feature, which restricts the close packing of the polymer chains and reduces inter-chain interactions, leads to amorphous poly(ether imide)s with good solubility in common organic solvents. In addition, the rigidity of the main chain of these polymers appears to be preserved due to the spiro-structure. As a result, these poly(ether imide)s exhibit a high T g and excellent thermal stability.

Analogs of Cinchona Alkaloids Incorporating a 9,9′‐Spirobifluorene Moiety

AbstractThe Cinchona alkaloid analogs (+)‐ and (−)‐5 with a quinuclidine‐2‐methanol residue attached to C(2) of a 9,9′‐spirobifluorene moiety were prepared as a racemic mixture by reacting lithiated 2‐bromo‐9,9′‐spirobifluorene 7 with (2‐ethoxycarbonyl)quinuclidine (±)‐6 to give ketone (±)‐8, followed by diastereoselective reduction with diisobutylaluminum hydride (DIBAL‐H). The absolute configuration at C(9) and C(8), i.e., at the methanol bridge and the adjacent quinuclidine C‐atom, in the two enantiomers of 5 is identical to the configuration at the corresponding centers in (−)‐quinine (1) and (+)‐quinidine (2), respectively. For the optical resolution of (±)‐5, a chiral stationary phase for HPLC was prepared by covalently bonding quinine via a thiol spacer to a silica‐gel surface. The enantiomer separation was accomplished at an α value of 1.61 with (±)‐5 being eluted last, in agreement with 1H‐NMR studies in CDCl3 which showed that (+)‐5 underwent a more stable host‐guest association with quinine than (−)‐5. 1H{1H} Nuclear Overhauser effect (NOE) difference spectroscopical analysis of the host‐guest associations with quinine in CDCl3, combined with computer‐model examinations, allowed the assignment of the absolute configurations as (+)‐(8R,9S)‐5 and (−)‐(8S,9R)‐5. A detailed conformational analysis displayed excellent agreement between the results of computational methods (Monte Carlo multiple minimum simulations, analyses of the total energy as a function of the flexible dihedral angles in the molecule) and 1H{1H}‐NOE difference spectroscopical data. It was found that (−)‐5 and (+)‐5 differ significantly in their conformational preference from their natural counterparts quinine (1) and quinidine (2). Whereas the natural alkaloids prefer the ‘open’ conformation, with the quinuclidine N‐atom pointing away from the quinoline ring, analog (±)‐5 adopts preferentially (by ca. 4 kcal mol−1) a ‘closed’ conformation, in which the quinuclidine N‐atom points into the cleft of the 9,9′‐spirobifluorene moiety. Since the basic quinuclidine N‐atom in the ‘closed’ conformation is sterically shielded from forming strong H‐bonds, the new Cinchona alkaloid analogs form less stable host‐guest associations via H‐bonding than quinine or quinidine.