Metal‐Free Facile Synthesis of Multisubstituted 1‐Aminoisoquinoline Derivatives with Dual‐State Emissions

Although isoquinoline is a good traditional fluorescent structural unit, most of its derivatives emit fluorescence in solution and a few of them can emit solid‐state fluorescence as well. Herein, a series of multisubstituted 1‐aminoisoquinoline derivatives were synthesized by a simple reaction of a readily available 4H‐pyran derivative and secondary amines. The reaction had advantages of metal‐free, mild conditions, simple operation, and good yields, which was realized by a ring‐opening and sequential ring‐closing mechanism. These 1‐aminoisoquinoline derivatives were found to exhibit interesting dual‐state emissions. In the solution, they emitted strong blue fluorescence at about 458 nm. In the solid state, they emitted solid‐state blue fluorescence at 444–468 nm with high fluorescence quantum yields of 40.3–98.1%. Crystal structural analyses indicated that solid‐state emissions of these compounds originated from twisted molecular conformations and the resultant loose stacking arrangements. Furthermore, their solid‐state fluorescence wavelengths were demonstrated to depend on molecular conformations rather than stacking arrangements. The discovery of these 1‐aminoisoquinolines with multiple reaction sites provides new possibilities for the development of solid‐state fluorescent materials based on the traditional isoquinoline skeleton.     

Ring‐Shaped Silafluorene Derivatives as Efficient Solid‐State UV‐Fluorophores: Synthesis,Characterization, and Photoluminescent Properties

Four ring‐shaped silafluorene‐containing compounds ( 1 – 4 ) were synthesized and characterized as potentially promising monomers for fluorescent polymers. Their optical properties in solution and solid state (thin film and powder) were studied. These compounds have low quantum yields in solution (Φ_fl=0.13‐0.15) with fluorescence maxima at about 355 nm, but high quantum yields in the solid state (powder, Φ_fl=0.35‐0.54) with fluorescence maxima at about 377 and 488 nm. Influence of the substituents and the number of silafluorene units in 1 – 4 on their optical properties was investigated. Extensive study of the X‐ray crystal structures of 1 – 4 was undertaken to analyze and qualitatively estimate the role, extent, and influence of silafluorene moieties’ interactions on solid‐state fluorescent properties. Excited state UV/Vis and theoretical molecular orbital (MO) calculations were performed to explore possible fluorescence mechanisms and differences in quantum yields among these compounds.     

2,5‐Difluorenyl‐Substituted Siloles for the Fabrication of High‐Performance Yellow Organic Light‐Emitting Diodes

2,3,4,5‐Tetraarylsiloles are a class of important luminogenic materials with efficient solid‐state emission and excellent electron‐transport capacity. However, those exhibiting outstanding electroluminescence properties are still rare. In this work, bulky 9,9‐dimethylfluorenyl, 9,9‐diphenylfluorenyl, and 9,9′‐spirobifluorenyl substituents were introduced into the 2,5‐positions of silole rings. The resulting 2,5‐difluorenyl‐substituted siloles are thermally stable and have low‐lying LUMO energy levels. Crystallographic analysis revealed that intramolecular π–π interactions are prone to form between 9,9′‐spirobifluorene units and phenyl rings at the 3,4‐positions of the silole ring. In the solution state, these new siloles show weak blue and green emission bands, arising from the fluorenyl groups and silole rings with a certain extension of π conjugation, respectively. With increasing substituent volume, intramolecular rotation is decreased, and thus the emissions of the present siloles gradually improved and they showed higher fluorescence quantum yields (Φ_F=2.5–5.4 %) than 2,3,4,5‐tetraphenylsiloles. They are highly emissive in solid films, with dominant green to yellow emissions and good solid‐state Φ_F values (75–88 %). Efficient organic light‐emitting diodes were fabricated by adopting them as host emitters and gave high luminance, current efficiency, and power efficiency of up to 44 100 cd m^?2, 18.3 cd A^?1, and 15.7 lm W^?1, respectively. Notably, a maximum external quantum efficiency of 5.5 % was achieved in an optimized device.     

Extended Fluorochromism of Anthracene Trimers with a meta‐Substituted Triphenylamine or Triphenylphosphine Core

Combining meta‐triphenylamine or triphenylphosphine with three anthracene fluorophores gives rise to fluorescent non‐planar triskelions 1 and 2 . The emissive properties of 1 are highly solvatochromic, yielding blue to pale green and even pale yellow fluorescence, whereas the blue emission of 2 is solvent‐insensitive. Anthracene trimers 1 and 2 are both emissive in the solid state, displaying yellow and pale green fluorescence, respectively, with moderate quantum yields.     

Highly Emissive Diborylphenylene‐Containing Bis(phenylethynyl)benzenes: Structure–Photophysical Property Correlations and Fluoride Ion Sensing

A series of 2,5‐bis(dimesitylboryl)‐1,4‐bis(arylethynyl)benzenes 1 – 6 that contain various p‐substituents on the terminal benzene rings, including NPh₂ ( 1 ), OMe ( 2 ), Me ( 3 ), H ( 4 ), CF₃ ( 5 ), and CN ( 6 ) groups, were synthesized, and the effects of the p‐substituents on the absorption and fluorescence properties were investigated both in solution and in the solid state. Linear relationships were obtained not only between the Hammett σ_p⁺ constants of the p‐substituents and the absorption and fluorescence maxima, quantum yields, and excited‐state dynamics parameters in solution, but also between the σ_p⁺ constants and the fluorescence quantum yields in the solid state. An important finding extracted from these results is that the suppressed fluorescence quenching in the solid state is a common feature for the present laterally boryl‐substituted π‐conjugated skeletons. Hence, the diborylphenylene can serve as a useful core unit to develop highly emissive organic solids. In fact, most of the derivatives showed more intense emission in the solid state than in solution. In addition to these studies, the titration experiment of 1 by the addition of nBu₄NF was conducted, which showed the stepwise bindings of two fluoride ions with high association constants as well as a drastic change in the fluorescence spectra, while constantly maintaining high quantum yields (0.61–0.76), irrespective of the binding modes. This result also demonstrated the potential utility of the present molecules as an efficient fluorescent fluoride ion sensor.     

Achieving Pure Deep‐Blue Electroluminescence with CIE y≤0.06 via a Rational Design Approach for Highly Efficient Non‐Doped Solution‐Processed Organic Light‐Emitting Diodes

Deep‐blue fluorescent emitters with Commission Internationale de l'Eclairage (CIE) y≤0.06 are urgently needed for high‐density storage, full‐color displays and solid‐state lighting. However, developing such emitters with high color purity and efficiency in solution‐processable non‐doped organic light‐emitting diodes (OLEDs) remains an important challenge. Here, we present the synthesis of two new deep‐blue fluorescent emitters ( AFpTPI and AFmTPI ) based on 10‐(9,9‐diethyl‐9H‐fluoren‐2‐yl)‐9,9‐dimethyl‐9,10‐dihydroacridine as a core and 1,3‐ and/or 1,4‐phenylene‐linked triphenylimidazole (TPI) analogues for non‐doped solution‐processable OLEDs. Their thermal, photophysical, electrochemical, and device characteristics are explored, and also strongly supported by density functional theory (DFT) study. AFpTPI and AFmTPI exhibit excellent thermal stability (≈450 °C) with high glass transition temperatures (T_g; 141–152 °C) and deep‐blue emission with high quantum yields. Specifically, the solution‐processed non‐doped device with AFpTPI as an emitter exhibits a maximum external quantum efficiency (EQE) of 4.56 % with CIE coordinates of (0.15, 0.06), which exactly matches the European Broadcasting Union (EBU) blue standard. In addition, AFmTPI also displays good efficiency and better color purity (EQE: 3.37 %; CIE (0.15, 0.05)). To the best of our knowledge, the present work is the first report on non‐doped solution‐processable OLEDs with efficiency close to 5 % and CIE y≤0.06.     

Pyrene‐Based Y‐shaped Solid‐State Blue Emitters: Synthesis,Characterization, and Photoluminescence

A series of pyrene‐based Y‐shaped blue emitters, namely, 7‐tert‐butyl‐1,3‐diarylpyrenes 4 were synthesized by the Suzuki cross‐coupling reaction of 7‐tert‐butyl‐1,3‐dibromopyrene with a variety of p‐substituted phenylboronic acids in good to excellent yields. These compounds were fully characterized by X‐ray crystallography, UV/Vis absorption and fluorescence spectroscopy, DFT calculations, thermogravimetric analysis, and differential scanning calorimetry. Single‐crystal X‐ray analysis revealed that the Y‐shaped arylpyrenes exhibited a low degree of π stacking owing to the steric effect of the bulky tert‐butyl group in the pyrene ring at the 7‐position, and thus, the intermolecular π–π interactions were effectively suppressed in the solid state. Despite the significantly twisted nonplanar structures, these molecules still displayed efficient intramolecular charge‐transfer emissions with clear solvatochromic shifts on increasing solvent polarity. An intriguing fact is that all of these molecules show highly blue emissions with excellent quantum yields in the solid state. Additionally, the two compounds containing the strongest electron‐accepting groups, CN ( 4d ) and CHO ( 4f ), possess high thermal stability, which, together with their excellent solid‐state fluorescence efficiency, makes them promising potential blue emitters in organic light‐emitting device applications.     

Luminescent poly(phenylene vinylene) derivatives with m‐terphenyl or 2,6‐diphenylpyridine kinked segments along the main chain: Synthesis,characterization, and stimulated emission

Two new poly(phenylene vinylene)s containing m‐terphenyl or 2,6‐diphenylpyridine kinked units along the main chain were synthesized and were used as luminescent and laser materials. They were prepared from Heck coupling of 2,5‐didodecyloxy‐1,4‐divinylbenzene with 4,4″‐dibromo‐3′‐phenyl‐m‐terphenyl or 2,6‐di(4‐bromophenyl)‐4‐phenylpyridine. The kinked units along the main chain caused a partial interruption of the conjugation leading to emission at a shorter wavelength as compared with poly(p‐phenylene vinylene). The polymers presented blue‐green emission in solution and green‐yellow emission in the solid state with photoluminescence maxima at 465–497 and 546–550 nm, respectively. Polymer containing 2,6‐diphenylpyridine segments emitted at a longer wavelength than that containing m‐terphenyl and displayed higher quantum yields in solution (0.61 and 0.40, respectively). The influence of the solvent and polymer concentration on the photoluminescence characteristics was investigated. The photoluminescence properties of protonated polymer containing 2,6‐diphenylpyridine segments were investigated both in solution and in film. Amplified spontaneous emission and tunable laser action were also obtained from the two polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2214–2224, 2004     

Functionalization of Quinoxalines by Using TMP Bases: Preparation of Tetracyclic Heterocycles with High Photoluminescene Quantum Yields

Tetracyclic heterocycles that exhibit high photoluminescence quantum yields were synthesized by anellation reactions of mono‐, di‐, and trifunctionalized 2,3‐dichloroquinoxalines. Thus, treatment of 2,3‐dichloroquinoxaline with TMPLi (TMP=2,2,6,6‐tetramethylpiperidyl) allows a regioselective lithiation in position 5. Quenching with various electrophiles (iodine, (BrCl₂C)₂, allylic bromide, acid chloride, aryl iodide) leads to 5‐functionalized 2,3‐dichloroquinoxalines. Further functionalization in positions 6 and 8 can be achieved by using TMPLi or TMPMgCl ? LiCl furnishing a range of new di‐ and tri‐functionalized 2,3‐dichloroquinoxalines. The chlorine atoms are readily substituted by anellation with 1,2‐diphenols or 1,2‐dithiophenols leading to a series of new tetracyclic compounds. These materials exhibit strong, tunable optical absorption and emission in the blue and green spectral region. The substituted O‐heterocyclic compounds exhibit particularly high photoluminescence quantum yields of up to 90 %, which renders them interesting candidates for fluorescence imaging applications.     

Luminescent Tungsten(VI) Complexes: Photophysics and Applicability to Organic Light‐Emitting Diodes and Photocatalysis

The synthesis, excited‐state dynamics, and applications of two series of air‐stable luminescent tungsten(VI) complexes are described. These tungsten(VI) complexes show phosphorescence in the solid state and in solutions with emission quantum yields up to 22 % in thin film (5 % in mCP) at room temperature. Complex 2 c , containing a 5,7‐diphenyl‐8‐hydroxyquinolinate ligand, displays prompt fluorescence (blue–green) and phosphorescence (red) of comparable intensity, which could be used for ratiometric luminescent sensing. Solution‐processed organic light‐emitting diodes (OLEDs) based on 1 d showed a stable yellow emission with an external quantum efficiency (EQE) and luminance up to 4.79 % and 1400 cd m⁻² respectively. These tungsten(VI) complexes were also applied in light‐induced aerobic oxidation reactions.     

Synthesis and Optical Properties of Novel Fluorescence‐Traced Benzimidazolium Bromides

Seven novel fluorescence‐traced 1‐aryl‐2‐substituted‐3‐allyl‐1H‐benzimidazolium bromides ( 5a , 5b , 5c , 5d , 5e , 5f , 5g ) were synthesized by alkylation and quaternization of compounds 1‐aryl‐2‐substituted‐1H‐benzimidazoles ( 4a , 4b , 4c , 4d , 4e , 4f , 4g ) with excess allyl bromide in acetonitrile at refluxing temperature. Their structures were characterized by ¹H‐NMR, MS, and elemental analysis. They emit violet‐blue light (λ^Em_max = 386–438 nm) with fluorescence quantum yields of 0.54 to 0.75 in aqueous solution.     

Polyfluorenes containing tetraphenylthiophene segments: Synthesis,photophysics, and electroluminescence

2,5‐Bis(4‐bromophenyl)‐3,4‐diphenylthiophene was synthesized from benzyl chloride and sulfur and through the subsequent bromination of the intermediate 2,3,4,5‐tetraphenylthiophene. It was condensed with 2,7‐dibromo‐9,9‐dihexylfluorene via a nickel‐mediated Yamamoto coupling reaction to afford a new series of statistical copolymers with various compositions. In addition, poly(9,9‐dihexylfluorene) (PF) was synthesized under the same conditions for comparison. All the polymers were soluble in common organic solvents such as tetrahydrofuran (THF), chloroform, and dichloromethane. Their glass‐transition temperatures increased with an increase in the tetraphenylthiophene (TPT) content in the polymers, and they were 63–149 °C. The solutions of the polymers in THF emitted intense blue light with a photoluminescence maximum at 418–440 nm and quantum yields of 0.32–0.62. Thin films of the polymers with TPT fractions lower than 20 mol % emitted blue‐green light with two well‐resolved peaks at 445 and 520 nm and an optical band gap of about 2.85 eV. A thin film of the polymer with aTPT fraction of 50 mol % emitted pure blue light with a maximum at 419 nm and an optical band gap of 3.28 eV. An enhancement of the light‐emitting‐diode brightness by a factor of ～8 with respect to that of PF was achieved in apolymer containing 5 mol % TPT. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4015–4026, 2006     

Preparation and Characterization of Substituted 3‐Benzothiazol‐2‐Ylcoumarins

A series of substituted 3‐benzothiazolylcoumarins was prepared from condensation of 2‐hydroxy‐benzaldehyde and 2‐cyanomethylbenzothiazole to investigate the effect of the nature and position of substituents on their absorption and fluorescent behavior. Compounds with a substituent containing a heteroatom which attached at the C6 position showed a split broad absorption band. Solutions of these compounds in various solvents exhibited brilliant blue fluorescence. The emission intensity for compounds with an alkoxy group at the C6 or C7 position in DMF was approximately 7‐ and 15‐fold higher than for the corresponding precursor and quinine sulfate solution, respectively. These compounds also exhibit high thermal stability in solid state.     

Synthesis of fluoro‐substituted silole‐containing conjugated materials

2,5‐Dihydroxyboryl‐1,1‐dimethyl‐3,4‐bis(3‐fluorophenyl)‐silole ( 2a ) was prepared in 40% overall yield by reaction between 3‐fluorophenyl‐acetylene and dichlorodimethylsilane to yield bis[2(3‐fluorophenyl)ethynyl]dimethylsilane ( 1a ), which subsequently undergoes a reductive cyclization reaction using an excess of lithium naphthalenide. The fluoro substituted silole was applied as a co‐monomer in the Suzuki polycondensation reaction with 2,7‐dibromo‐9,9‐dioctyl‐fluorene. An oligomer ( 3a ) with a degree of polymerization of 6 was prepared and compared with an oligomer without fluoro substitution on the silole ( 3b ), with a degree of polymerization of 4. The new oligomers were spin coated onto glass slides and showed weak green photoluminescence (PL) in the solid state. Cyclic voltammetry, visible absorption spectroscopy, and density functional theory calculations showed that the fluoro substituents were sufficiently electron withdrawing to lower both the highest occupied molecular orbital and the lowest unoccupied molecular orbital in the oligomer. Two further alternating co‐oligomers were prepared from 2,5‐dihydroxyboryl‐1,1‐dimethyl‐3,4‐bis(phenyl)‐silole ( 2b ) and 1,3‐dibromo‐5‐fluoro‐benzene ( 4a ) or 1,3‐dibromobenzene ( 4b ). These oligomers both had degrees of polymerization of 8 and showed green PL in the solid state. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5116–5125, 2009     

5,12‐Diacetyl‐5,12‐dihydroquinoxalino[2,3‐b]quinoxalines: Solid‐State Fluorescence,AIE Properties,and Orbital Switching by Substituent Effect

The compound 5,12‐diacetyl‐5,12‐dihydroquinoxalino[2,3‐b]quinoxaline 1 a and its derivatives were prepared, and their solid‐ and solution‐state spectroscopic properties were studied; 1 a shows stronger fluorescence in solution than in the solid state due to aggregation caused by self‐quenching. Phenyl‐ or alkoxy‐substituted derivatives 1 b – d show solid‐state fluorescence with moderate quantum yields of about Φ=0.12–0.15, although the corresponding values are 0.01–0.07 in solution. The spectroscopic properties of alkoxy‐substituted derivatives were hardly changed compared to 1 a and 1 b , although 1 a and 1 b have similar absorption and fluorescence maxima in solution and in the solid state. DFT calculations indicate that orbital switching occurs between HOMO and HOMO‐1 and HOMO‐2 due to orbital interactions with introduced substituents. Crystal structure analysis revealed that the molecules have bent structures around tertiary nitrogen atoms and form a characteristic dimeric structure.     

π‐conjugated polymers having diaza[12]annulene rings and aminopenta‐2,4‐dienylidene groups generated by the ring opening of pyridinium rings

Reactions of N‐(2,4‐dinitrophenyl)pyridinium chloride with 2,5‐dimethyl‐1,4‐phenylenediamine in 1:2, 1:1.5, 1:1, and 2:1 molar ratios caused the ring opening of the pyridinium ring and thereby yielded polymers ( P1 – P4 ) consisting of 5‐(2,5‐dimethyl‐1,4‐phenylene)penta‐2,4‐dienylideneammonium chloride (unit A) and N‐2,5‐dimethyl‐1,4‐phenylene diaza[12]annulenium dichloride (unit B). The ¹H NMR spectra suggested that the composition ratios of unit A to unit B in P1 – P4 were 0.98:0.02, 0.94:0.06, 0.81:0.19, and 0.79:0.21, respectively. P1 – P4 showed an absorption maximum (λ_max) at a longer wavelength than the monomers because of the expansion of the π‐conjugation system. Films of P3 and P4 showed λ_max at a considerably longer wavelength than those in solution, and this was attributable to the ordered structures of the polymers in the solid state. Powder X‐ray diffraction analysis supported the ordered structures of P3 and P4 . Pellets molded from P3 and P4 exhibited a metallic luster, whereas those from P1 and P2 did not show such a luster. Cyclic voltammetry measurements indicated that P1 – P4 were electrochemically active in films. The thermal stability of the polymers depended on the composition ratios of unit A to unit B. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1507–1514, 2007     

Membrane Damage Efficiency of Phenothiazinium Photosensitizers

Structure–activity relationships have been widely reported for porphyrin and phthalocyanine photosensitizers, but not for phenothiazinium derivatives. Here, four phenothiazinium salts (methylene blue, toluidine blue O, 1,9‐dimethyl methylene blue and the pentacyclic derivative DO15) were used to investigate how the ability to damage membranes is affected by membrane/solution partition, photophysical properties and tendency to aggregation of the photosensitizer. These two latter aspects were studied both in isotropic solutions and in membranes. Membrane damage was assessed by leakage of a fluorescent probe entrapped in liposomes and by generation of thiobarbituric acid‐reactive species (TBARS), while structural changes at the lipid bilayer were detected by small‐angle X‐ray scattering. We observed that all compounds had similar singlet‐oxygen quantum yields in ethanol, but only the photosensitizers that had higher membrane/solution partition (1,9‐dimethyl methylene blue and DO15, the latter having the higher value) could permeabilize the lipid bilayer. Moreover, of these two photosensitizers, only DO15 altered membrane structure, a result that was attributed to its destabilization of higher order aggregates, generation of higher amounts of singlet oxygen within the membranes and effective electron‐transfer reaction within its dimers. We concluded that membrane‐based protocols can provide a better insight on the photodynamic efficiency of the photosensitizer.     

Preparation of ferrocene-containing phosphinamine ligands possessing central and planar chirality and their application in palladium-catalyzed asymmetric allylic alkylation

The preparation of [2-(S(p))-[(trans-(2R,5R)-2,5-dialkylpyrrolidinyl)methyl]]ferrocenyldiphenyl phosphines, new ferrocenylphosphinamine ligands possessing one site of planar and two stereogenic centers, is described. trans-(2R,5R)-2,5-Dialkyl-1-(ferrocenylmethyl)pyrrolidines were diastereoselectively lithiated and quenched with chlorodiphenylphosphine. For the dimethyl ligand, chemical yields of up to 65% and des of up to 90% were obtained whereas the diethyl ligand afforded lower chemical yields (10%) and des of 78%. Diastereomerically pure material was obtained in both cases after a single recrystallization from ethanol. (S)-Planar chirality was confirmed by X-ray crystallographic analysis of the dimethyl ligand. The palladium complexes of the new ligands were applied in the allylic alkylation of 1,3-diphenylprop-2-enyl acetate with reasonable chemical yields and moderate ees of up to 36% and 38% when dimethyl malonate and dimethyl methyl malonate were employed as nucleophiles, respectively. Importantly, it was found that the new ligands possessing the combination of planar and central chirality gave the opposite enantiomeric alkylation products compared to ligands which possess only the central chirality of the trans-2,5-dimethylpyrrolidinyl moiety. Solution NMR studies of the 1,3-diphenylallyl palladium complex of the dimethyl ligand revealed the presence of only the exo-configured allyl diastereomer.     

Alkylation‐, Heating‐, and Doping‐Induced Emission Enhancement of a Polyaromatic Tube in the Solid State

A polyaromatic tube with a subnanometer‐sized cavity was efficiently prepared on a gram‐scale through the stereo‐controlled cyclotrimerization of a diphenylanthracene derivative as a key step. The facile exterior alkylation of the polyaromatic framework leads to a moderately fluorescent tube (R=‐OC₁₀H₂₁; Φ_F=20 %) in the solid state. The emission intensity of the solid‐state alkyl‐substituted tube is remarkably enhanced upon heating (up to 1.6 times, Φ_F=31 %) as well as doping with fluorescent dyes (up to 4.2 times, Φ_F=83 %) through efficient energy transfer.     

Luminescence Color Tuning from Blue to Near Infrared of Stable Luminescent Solid Materials Based on Bis‐o‐Carborane‐Substituted Oligoacenes

Aryl‐substituted o ‐carboranes have shown highly efficient solid‐state emission in previous studies. To demonstrate color tuning of the solid‐state emission in an aryl‐o ‐carborane‐based system, bis‐o ‐carborane‐substituted oligoacenes were synthesized and their properties were systematically investigated. Optical and electrochemical measurements revealed efficient decreases in energy band gaps and lowest unoccupied molecular orbital (LUMO) levels by adding a number of fused benzene rings for the extension of π‐conjugation. As a consequence, bright solid‐state emission was observed in the region from blue to near infrared (NIR). Furthermore, various useful features were obtained from the modified o ‐carboranes as an optical material. The naphthalene derivatives exhibited aggregation‐induced emission (AIE) and almost 100 % quantum efficiency in the crystalline state. Furthermore, it was shown that the tetracene derivative with NIR‐emissive properties had high durability toward photo‐bleaching under UV irradiation.