Blue light emitting polymers

Fluorescent Aromatic Polyether Sulfones: Processable, Scalable, Efficient, and Stable Polymer Emitters and Their Single-Layer Polymer Light-Emitting Diodes

In this study, fully aromatic polyether sulfones were developed, bearing blue, yellow, and orange-red π-conjugated semiconducting units. Carbazole-, anthracene-, and benzothiadiazole-based fluorophores are copolymerized with a diphenylsulfone moiety. A diphenylpyridine comonomer was additionally utilized, acting as both a solubilizing unit and a weak blue fluorescent group. Using this rationale, fluorescent polyarylethers with high molecular weights, up to 70 kDa, were developed, showing film formation ability and high thermal stability, while preserving excellent solubility in common organic, nonvolatile, and nonchlorinated solvents. Fine-tuning of the emission color was achieved through subtle changes of the comonomers' type and ratio. Single-chromophore-bearing copolymers emitted in the blue or the yellow region of the visible spectrum, while the dual-chromophore-bearing terpolymers emitted throughout the visible spectrum, resulting in white light emission. Solutions of 20 wt% in polar aprotic solvents at ambient conditions allowed the deposition of fluorescent copolyethers and printing from non-chlorinated solvents. All polyethers were evaluated for their structural and optoelectronic properties, and selected copolymers were successfully used in the emitting layer (EML) of organic light-emitting diode (OLED) devices, using either rigid or flexible substrates. Remarkable color stability was displayed in all cases for up to 15 V of bias voltage. The Commission Internationale de L'Eclairage (CIE) of the fabricated devices is located in the blue (0.16, 0.16), yellow (0.44, 0.50), or white region of the visible spectrum (0.33, 0.38) with minimal changes according to the ratio of the comonomers. The versatile methodology toward semiconducting polyethersulfones for polymer light-emitting diodes (PLEDs) developed herein led to the scaled-up production of luminescent polymers of up to 25 g of high-molecular-weight single batches, demonstrating the effectiveness of this approach as a straightforward tool to facilitate the synthesis of flexible and printable EMLs for large-area PLED coverage.

Unconventional Pathway in the Gas-Phase Synthesis of 9H-Fluorene (C13 H10 ) via the Radical-Radical Reaction of Benzyl (C7 H7 ) with Phenyl (C6 H5 )

The simplest polycyclic aromatic hydrocarbon (PAH) carrying a five-membered ring-9H-fluorene (C₁₃ H₁₀ )-is produced isomer-specifically in the gas phase by reacting benzyl (C₇ H₇ ⋅) with phenyl (C₆ H₅ ⋅) radicals in a pyrolytic reactor coupled with single photon ionization mass spectrometry. The unconventional mechanism of reaction is supported by theoretical calculations, which first produces diphenylmethane and unexpected 1-(6-methylenecyclohexa-2,4-dienyl)benzene intermediates (C₁₃ H₁₂ ) accessed via addition of the phenyl radical to the ortho position of the benzyl radical. These findings offer convincing evidence for molecular mass growth processes defying conventional wisdom that radical-radical reactions are initiated through recombination at their radical centers. The structure of 9H-fluorene acts as a molecular building block for complex curved nanostructures like fullerenes and nanobowls providing fundamental insights into the hydrocarbon evolution in high temperature settings.

Efficient Energy Funneling in Spatially Tailored Segmented Conjugated Block Copolymer Nanofiber-Quantum Dot or Rod Conjugates

Hybrid systems composed of conjugated polymers and inorganic semiconductor nanocrystals such as quantum dots (QDs) and nanorods (QRs) represent highly desirable multifunctional materials for applications from energy harvesting to light emission and sensing. Herein, we describe energy transfer studies between low-dispersity segmented conjugated polymer micellar nanofibers integrated with quantum dots that are spatially confined to discrete regions in the hybrid assembly via noncovalent interactions. The nanofibers were prepared from diblock copolymers with a crystallizable poly(di-n-hexylfluorene) (PDHF) core-forming block and different corona-forming blocks using the seeded-growth "living" crystallization-driven self-assembly method. The highly ordered crystalline PDHF core in the fibers functions as a donor and permits long-range exciton transport (>200 nm). Energy can therefore be funneled through the fiber core to QDs and QRs that function as acceptor materials and which are noncovalently bound to spatially defined coronal regions of poly(2-vinylpyridine) (P2VP) or quaternized polyfluorene (QPF). Using steady-state and time-resolved spectroscopy, we demonstrate that efficient energy transfer (over 70%) occurs from the crystalline PDHF donor core to the acceptor CdSe QRs attached at the fiber termini. The emission of the PDHF donor in the hybrid conjugate was extensively quenched (by 84%), and a subsequent 4-fold enhancement of the QR emission in solution was observed. These results indicate that the conjugates prepared in this work show promise for potential applications in fields such as light-emitting diodes, photovoltaics, chemical sensors, and photocatalysis.

(Poly)terephthalates with Efficient Blue Emission in the Solid State

We prepared dimethyl and diaryl 2,5-dialkoxytere-phthalates from dimethyl 2,5-dihydroxyterephthalate in good-to-high yields via alkylation or a sequence of alkylation, hydrolysis, chlorination, and condensation. The absorption spectra of the dialkoxyterephthalates contain a small band at 332-355 nm, which could be assigned to intramolecular charge-transfer transition from the alkoxy to alkoxycarbonyl groups on the basis of theoretical calculations using density functional theory. The dialkoxyterephthalates exhibited blue fluorescence with moderate-to-excellent quantum yields not only in solution but also in the solid state, such as a poly(methyl methacrylate) (PMMA) film and a powder. The solid-state quantum yields of the diisopropoxy-substituted terephthalates were similar or considerably higher than those of the dimethoxy-substituted counterparts. Copolymerization of 2,5-diisopropoxyterephthaloyl chloride and 1,4-butanediol with or without terephthaloyl chloride gave brilliantly blue fluorescent polymers, whose quantum yields were 0.72 and 0.71 in toluene and 0.46 and 0.40 in the neat film, respectively. Furthermore, white emission was achieved when a fluorescent yellow 2,5-diaminoterephthalate was doped into the thin film of the blue fluorescent polymer at 0.4 wt %.

A New Candidate Laser Dye Based 1,4-Bis[β-(2-Naphthothiazolyle)Vinyl]Benzene. Spectroscopic Behavior, Laser Parameters and Excitation Energy Transfer

A new candidate laser dye based 1,4-bis[β-(2-naphthothisolyl) vinyl] benzene (BNTVB) were prepared, and characterized in various organic solvents. The center polarity is less sensitive than electronic absorption. A red shift was noticed in the fluorescence spectra (ca. 40 nm) with increment in the solvent's polarity, this means that BNTVB's polarity appreciates upon excitation. The dipole moment of ground state (μ_g) and the excited singlet state dipole moment (μ_e) are determined from Kawski - Chamma and Bakshiev-Viallet equations using the disparity of Stokes shift with solvent polarity function of ε (dielectric constant) and n (refractive index) of the solvent. The result was found to be 0.019D and 5.13D for ground and exited state, in succession. DFT/TD-DFT manners were used to understand the electronic structures and geometric of BNTVB in other solvents. The experimental and theoretical results showed a good agreement. The photochemical quantum yield (Ф_c) of BNTVB was calculated in variable organic reagents such as Dioxane, CHCl₃, EtOH and MeOH at room temperature. The values of φ_c were calculated as 2.3 × 10^-4, 3.3 × 10^-3, 9.7 × 10^-5 and 6.2 × 10^-5 in Dioxane, CHCl₃, EtOH and MeOH, respectively. The dye solutions (2 × 10^-4 M) in DMF, MeOH and EtOH give laser emission in the blue-green region. The green zone is excited by nitrogen pulse 337.1 nm. The tuning range, gain coefficient (α) and cross - section emission (σ_e) of laser were also estimated. Excitation energy transfer from BNTVB to rhodamine-6G (R6G) and N,N-bis(2,6-dimethyphenyl)-3,4:9,10-perylenebis-(dicarboximide) (BDP) was also studied in EtOH to increase the laser emission output from R6G and BDP when excited by nitrogen laser. The dye-transfer power laser system (ETDL) obeys the Foster Power Transmission (FERT) mechanism with a critical transmission distance, R_o of 40 and 32 Ả and k_ET equals 2.6 × 10¹³ and 1.06 × 10¹³ M^-1 s^-1 for BNTVB / R6G and BNTVB / BDP pair, respectively.

Synthesis and properties of blue luminescent bipolar materials constructed with carbazole and anthracene units with 4-cyanophenyl substitute at the 9-position of the carbazole unit

With carbazole and p-cyanobromobenzene as raw materials, 4-(3,6-di (anthracen-9-yl)-9H-carbazol-9-yl)benzonitrile (DACB) and 4-(3,6-bis(anthracene -9-ylethynyl)-9H-carbazol-9-yl)benzonitrile (BACB) were synthesized through the Suzuki coupling reaction and the Sonogashira coupling reaction, respectively. These structures were characterized using ¹ H nuclear magnetic resonance (NMR), elemental analysis and mass spectrometry. Their thermal properties, ultraviolet-visible (UV-vis) absorption, fluorescence emission, fluorescence quantum yields and electrochemical properties were also investigated systematically. In addition, a electroluminescence (EL) device was made with BACB as the emitting layer and performance of the EL device was studied. Results showed that: (1) the temperature points with 5% and 10% of DACB weight loss were 443°C and 461°C, respectively, and were 475°C and 506°C with BACB weight loss of 5% and 10%, respectively. When the temperature was 50-300°C, no significantly thermal transition was observed which suggested that they had excellent thermal stability. (2) DACB and BACB had single emission peaks at 415 nm, and 479 nm with fluorescence quantum yields of 0.61 and 0.87, respectively, indicating that both compounds could emit strong blue light. (3) According to electrochemical measurement on BACB and DACB, their gaps were 3.07 eV and 2.76 eV, respectively, which further showed that these two compounds were very stable and acted as efficient blue light materials. (4) The turn-on voltage of the device was 5 V, and the device emitted dark blue light with Commission Internationale de L'Eclairage (CIE) coordinates of (0.157, 0.079).

Conjugated Polymers Containing BODIPY and Fluorene Units for Sensitive Detection of CN- Ions: Site-Selective Synthesis, Photo-Physical and Electrochemical Properties

Conjugated polymers containing distinct molecular units are expected to be very interesting because of their unique properties endowed by these units and the formed conjugated polymers. Herein, four new conjugated copolymers based on fluorene and 4,4’-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) have been designed and synthesized via Sonogashira polymerization. The fluorene unit was attached to the 3,5- or 2,6-positions of BODIPY by ethynylenes or p-diacetylenebenzene. The obtained polymers show good thermal stability and broad absorption in the wavelength range from 300 to 750 nm. The effects of site-selective copolymerization and conjugation length along the polymer backbone on the optoelectronic and electrochemical properties of these copolymers were systematically studied by UV-Vis spectroscopy, photoluminescence (PL) and cyclic voltammetry. Besides, it is found that the BODIPY-based copolymers exhibit selectively sensitive responses to cyanide anions, resulting in obvious change of UV-Vis absorption spectra and significant fluorescence quenching of the polymers among various common anions.

Highly emissive carbazole-functionalized homopoly(spirobifluorene) for deep-blue polymer light-emitting diodes

By fully replacing the alkyloxy side chain with a carbazole, a highly emissive homopolymer P(Cz-SF) is developed for deep-blue PLEDs.

Synthesis and AIE properties of PEG–PLA–PMPC based triblock amphiphilic biodegradable polymers

The synthesis of a novel AIE-active micelle based on living immortal polymerization of cyclic esters and a “click” reaction of azide functionalized TPE is described.

Optical Absorptions of New Blue-Light Emitting Oligoquinolines Bearing Pyrenyl and Triphenyl Endgroups Investigated with Time-Dependent Density Functional Theory

The optical absorption spectra of a family of four n-type conjugated oligomers, oligoquinolines, which can be commercially used to develop high-performance light-emitting diodes for their many desirable properties, have been recently calculated from time-depedent density functional theory (TDDFT) within the adiabatic approximation for the dynamical exchange-correlation potential. In this work, we investigate the optical absorption of two new family members of the blue-light emitting oligoquinolines bearing pyrenyl and triphenyl endgroups in gas phase and chloroform (CHCl3) solution employing the adiabatic TDDFT. The ionization potentials and electron affinities of these two oligoquinoline molecules are also calculated with the ground-state DFT, from which the adiabatic dynamical exchange-correlation potential is constructed. We show that the calculated optical absorptions are in good agreement with experiments. The ionization potentials obtained with the DFT methods agree well with the experimental estimates, while the electron affinities are significantly underestimated in comparison with experiments. A natural transition orbital analysis for selected excited states with the largest oscillator strengths shows that the electronic charge is slightly redistributed in the process of electronic excitations.

Synthesis, Spectral Characteristics and DFT Studies of the New Dye 2,7-diacetyl-9-((dimethylamino)methylene)-9H-fluorene (DMMF) in Different Solvents

The photophysical parameters such as electronic absorption spectra, molar absorptivity(ε), fluorescence spectra and fluorescence quantum yield (φf) of a new dye namely 2,7-diacetyl-9-((dimethylamino)methylene)-9H-fluorene (DMMF) were determined in different solvents. The electronic absorption are less sensitive to medium polarity. A bathochromic shift was observed in emission spectra(ca. 50 nm) upon increase of solvent polarity, which indicates that the singlet excited state (S1) of DMMF is more polar than the singlet ground state (So). Solid crystals of DMMF exhibit intense yellow fluorescence maximum at 550 nm with bandwidth equal 64 nm upon excitation at wavelength 365 nm. The change in dipole moment value (Δμ) was calculated by using the variation of Stokes shift with solvent polarizability (Δf) (Lippert - Mataga plot) and was found to be 7.22 and 5.5 Debye for higher and lower energy of So - S1 (π-π*) H-1 → L and So - S1 (π-π*) H → L, respectively. These results show that, the excited state is more polar than the ground state. The net photochemical quantum yields of photodecomposition of DMMF (φc) were calculated as 7.2 × 10(-5), 1.14 × 10(-4), 1.44 × 10(-4) and 2.11 × 10(-4) in different solvents such as MeOH, CH2Cl2, CHCl3 and CCl4, respectively. DFT/TD-DFT methods were used to study the geometric and electronic structures of DMMF in different solvents. A good agreement was found between the experimental and theoretical results.

Enhancement of polymer endurance to UV light by incorporation of semiconductor nanoparticles

Improvement of polyvinyl alcohol stability against ultraviolet (UV) illumination is achieved by introducing cadmium sulfide (CdS) nanoparticles into the polymeric matrix. Enhancement of stability is analyzed by optical characterization methods. UV protection is achieved by diminishing the probability of photo-activated formation of defects in polymer. The sources of polymer protection are the lowering of the efficiency of polymer excitation via partial absorption of incident light by the embedded nanoparticles as well as the de-excitation of the macromolecules that have already absorbed UV quanta via energy drain to nanoparticles. Within the nanoparticles, the energy is either dissipated by conversion to the thermal energy or reemitted as visible-range photoluminescence quanta.

Efficient bifunctional materials based on pyrene- and triphenylamine-functionalized dendrimers for electroluminescent devices

These materials show a promising bifunctional property as blue emissive layer and hole-transporting layer for high efficiency solution processed blue and Alq3-based green OLEDs with much simpler device architecture.

Oligoarylenes end-capped with carbazol-N-yl-carbazole as color tunable light-emitting and hole-transporting materials for solution-processed OLEDs

A series of oligoarylenes (CAr) exhibited blue to red fluorescence with hole-transporting properties. Simple structured solution-processed CAr-based OLEDs emitted stable colors spanning the visible spectrum and white light with luminance efficiencies up to 13.73 cd A⁻¹.

Organic amorphous hole-transporting materials based on Tröger's Base: alternatives to NPB

New Hole-Transporting Materials (HTMs) based on Tröger's Base scaffold serve as respectable alternatives of NPB with high T_gs.

Organic–inorganic hybrid polyvinylidene fluoride–Co0.6Zn0.4Mn0.3Fe1.7O4 nanocomposite film with significant optical and magnetodielectric properties

In this paper, we illustrate the significant optical and magnetodielectric properties of the polyvinylidene difluoride–Co_0.6Zn_0.4Mn_0.3Fe_1.7O₄ nanocomposite film, containing the optimum weight content (0.5%) of CZFMO nanoparticles.

(Photo)physical Properties of New Molecular Glasses End-Capped with Thiophene Rings Composed of Diimide and Imine Units

New symmetrical arylene bisimide derivatives formed by using electron-donating-electron-accepting systems were synthesized. They consist of a phthalic diimide or naphthalenediimide core and imine linkages and are end-capped with thiophene, bithiophene, and (ethylenedioxy)thiophene units. Moreover, polymers were obtained from a new diamine, N,N'-bis(5-aminonaphthalenyl)naphthalene-1,4,5,8-dicarboximide and 2,5-thiophenedicarboxaldehyde or 2,2'-bithiophene-5,5'-dicarboxaldehyde. The prepared azomethine diimides exhibited glass-forming properties. The obtained compounds emitted blue light with the emission maximum at 470 nm. The value of the absorption coefficient was determined as a function of the photon energy using spectroscopic ellipsometry. All compounds are electrochemically active and undergo reversible electrochemical reduction and irreversible oxidation processes as was found in cyclic voltammetry and differential pulse voltammetry (DPV) studies. They exhibited a low electrochemically (DPV) calculated energy band gap (E_g) from 1.14 to 1.70 eV. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels and E_g were additionally calculated theoretically by density functional theory at the B3LYP/6-31G(d,p) level. The photovoltaic properties of two model compounds as the active layer in organic solar cells in the configuration indium tin oxide/poly(3,4-(ethylenedioxy)thiophene):poly(styrenesulfonate)/active layer/Al under an illumination of 1.3 mW/cm² were studied. The device comprising poly(3-hexylthiophene) with the compound end-capped with bithiophene rings showed the highest value of V_oc (above 1 V). The conversion efficiency of the fabricated solar cell was in the range of 0.69-0.90%.

Tuning of polyarylene ether nitrile emission profile by using red-emitting gold nanoclusters via fluorescence resonance energy transfer

The fluorescent emission of polyarylene ether nitrile can be modulated with gold nanoclusters via FRET.