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The optical gain of blue light-emitting electrospun polystyrene fibers doped with a linear multi-fragment molecular dye based on the combination of fluorine-carbazole functional units is investigated, with the aim of correlating emission properties and the specific material architecture made of either aligned or disordered fibers. Enhanced performance is found in aligned fibers, whose gain spectrum can be finely tuned by varying the dye concentration. Instead, randomly oriented fibers show a manifold spectral line narrowing, resulting in sharp laser peaks superimposed on top of a broad emission band, ascribable to random lasing. In these systems, the increase of the dye content turns out to be effective for both decreasing the lasing threshold by about a factor 6 and for varying the laser emission wavelength. These results make these arrays and disordered architectures of fibers valuable active media for variable-gain, broadband lasing, which is remarkably important in optical sensing and tunable microlaser devices., Comment: 24 pages, 12 Figures, 1 Table, Journal of Materials Chemistry C, 2022

Using the newly designed exciplex-forming 1,2,3-triazole-based acceptors with fast and efficient singlet → triplet intersystem crossing (ISC) processes, carbazole and benzoyl-1

Using the newly designed exciplex-forming 1,2,3-triazole-based acceptors with fast and efficient singlet → triplet intersystem crossing (ISC) processes, carbazole and benzoyl-1H-1,2,3-triazole derivatives were synthesized by Dimroth-type 1,2,3-triazole ring formation and Ullmann-Goldberg C-N coupling reactions. Due to the exciplex formation between covalently bonded electron-donating (carbazole) and 1,2,3-triazole-based electron-accepting moieties with small singlet-triplet splitting (0.07-0.13 eV), the compounds exhibited ISC-assisted bluish-green thermally activated delayed fluorescence. The compounds were characterized by high triplet energy levels ranging from 2.93 to 2.98 eV. The most efficient exciplex-type thermally activated delayed fluorescence was observed for ortho-substituted carbazole-benzoyl-1H-1,2,3-triazole which was selected as a host in the structure of efficient solution-processed white light-emitting diodes. The best device exhibited a maximum power efficiency of 10.7 lm/W, current efficiency of 18.4 cd/A, and quantum efficiency of 7.1%. This device also showed the highest brightness exceeding 10 thousand cd/m2. Usage of the exciplex-forming host allowed us to achieve a low turn-on voltage of 3.6 V. High-quality white electroluminescence was obtained with the close to nature white color coordinates (0.31, 0.34) and a color rendering index of 92.

The anionic ring-opening polymerization of carbazole-containing monomers, (9-carbazolylmethyl)thiirane (M1) and (3,6-di-tert-butyl-9-carbazolylmethyl)thiirane (M2), with hexanethiol or pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) as initiators and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as catalyst at 20 °C in tetrahydrofuran or N,N-dimethylformamide as solvents has been studied. The polymerization of these monomers proceeds in a living fashion affording linear and star-shaped polymers with controlled molecular weight (Mn = 4000–15,000 g mol−1) and relatively low polydispersity (Đ

Isomeric 3,6-dimethoxy- and 2,7-dimethoxycarbazoles containing diphenylethenyl moieties were synthesized by condensation of the appropriate dimethoxycarbazoles with diphenylacetaldehyde. The solid-state structures and the molecular order of the compounds were proven by X-ray crystallography. Both compounds were found to be capable of glass formation with comparable glass transition temperatures (70–71 °C). They exhibited high thermal stabilities, with the 5% weight loss temperatures exceeding 375 °C. The isomer having diphenylethenyl groups at C-3 and C-6 positions and methoxy groups at C-2 and C-7 positions (3a) exhibited aggregation-induced emission (AIE), while its counterpart having diphenylethenyl groups at C-2 and C-7 positions and methoxy groups at C-3 and C-6 positions (3b) showed the opposite effect, i.e. aggregation-caused quenching (ACQ). The derivative 3b showed superior charge transporting properties. Time-of-flight hole drift mobilities in its layers approached 10−3 cm2 V−1 s−1 at high electric fields. A comparative theoretical analysis of the compounds was performed using density functional theory (DFT) and time-dependent DFT calculations. They proved more effective π-conjugation in the derivative of 3,6-dimethoxy carbazole (3b), which was also observed by UV and fluorescence spectroscopies. The theoretical study revealed relatively low ground state dipole moment of 0.69 D of the isomer 3b, while its counterpart (3a) showed much higher ground state dipole moment of 5.98 D. The difference in polarity was found to have the crucial effect on the molecular arrangement in the crystals and consequently, on the thermal transitions and charge-transporting properties.

Random lasers are based on disordered materials with optical gain. These devices can exhibit either intensity or resonant feedback, relying on diffusive or interference behaviour of light, respectively, which leads to either coupling or independent operation of lasing modes. We study for the first time these regimes in complex, solid-state nanostructured materials. The number of lasing modes and their intensity correlation features are found to be tailorable in random lasers made of light-emitting, electrospun polymer fibers upon nanoparticle doping. By material engineering, directional waveguiding along the length of fibers is found to be relevant to enhance mode correlation in both intensity feedback and resonant feedback random lasing. The here reported findings can be used to establish new design rules for tuning the emission of nano-lasers and correlation properties by means of the compositional and morphological properties of complex nanostructured materials., 30 pages, 10 figures

Four carbazol-9-yl and diphenylamino substituted 9-ethylcarbazole derivatives having cyano groups in the substituents were synthesized and characterized by the experimental and theoretical tools. Thermal, optical, photophysical and electrochemical properties were studied. The derivatives exhibited moderate thermal stability with 5% weight loss temperatures exceeding 300 °C. All the derivatives were found to be capable of glass formation with glass transition temperatures ranging from 77 to 111 °C. The optical band gaps of the solid samples were 2.84–3.38 eV. One of the derivatives was used for the preparation of blue non-doped emitting layer and as exciplex forming material for the fabrication of blue and yellow organic light emitting diodes with CIE color coordinates of (0.17, 0.28) and (0.40, 0.52), respectively. The electroluminescence of the yellow exciplexes based device resulted from the overlapping of sky blue bulk emission with photoluminescence quantum efficiency of 43.8% and orange interface exciplex emission with the efficiency of 3.84%. The fluorescent non-doped blue OLED exhibited maximum luminance of 2515 cd/m2 and external quantum efficiency reaching of 2%, while the yellow exciplex OLED exploiting the effect of thermally activated delayed fluorescence had maximum luminance of 6260 cd/m2 and external quantum efficiency of 5.8%. In addition, sky-blue and orange OLEDs with only one exciplex-based emitter were fabricated showing external quantum efficiencies of 4.2 and 3.2%, respectively. This work provides background for the fabrication of efficient OLEDs combining advantages of both interface and bulk exciplex emissions (maximal internal quantum efficiency of 100%, provision of exelent charge balance in emitting layer, formation of the “active” planar pn heterojunctions).

International audience; Two new star-shaped carbazole molecules, including tri(9-(methoxyphenyl)carbazol-3-yl)amine named TMPCA having molecular glasses properties and hole transport properties were synthesized. Their thermal, optical, photophysical and electrochemical properties were studied. The carbazole based molecules exhibit high thermal stability with 5% weight loss temperatures over 480 °C with higher glass temperature transitions 164-175 °C than the classical spiro-OMeTAD reference molecule. Their optical band gaps (2.76 eV) are low enough not to hinder neither the absorption of the indoline sensitizer (D102) nor its photoexcitation and charge transfer. Solid state ionization potential (IPs) of TMPCA is well adapted to that of D102 and ensure a driving force ΔrG >0.2 eV for an efficient transfer and regeneration of the photo-oxidized dye. Solid-state dye sensitized solar cells ITO/TiO2/D102/T4MPCA/Au showed a power conversion efficiency of 2.23% with Jsc of 8.85 mA cm−2 under standard AM 1.5 simulated solar irradiation.

International audience; Efficient molecular glasses based on carbazole moiety used as hole transporting materials were synthesized. The role of the mono- or di-substitution of dimethoxy-diphenyl amine groups on the 3 and/or 6 position of the carbazole was evidenced. Their thermal, optical, photoelectrical, electrochemical properties as well as their photovoltaic characteristics on solid-state dye sensitized solar cells were investigated. The performance of these materials in solid-state DSSC based on TiO2 sensitized with the commercial indoline organic dye D102 is widely discussed. In such configuration, a power conversion efficiency of 3.4% and a fill factor of 0.53 are achieved with a 3,6-substitued carbazole molecular glass derivative, under standard AM 1.5 simulated solar irradiation. In addition, the Jsc value is even higher than the spiro-OMeTAD, due to its higher mobility. These results are found to be very promising since no specific optimization was performed on the devices yet. By comparison, the corresponding reference device incorporating spiro-OMeTAD as p-type organic semiconductor gives similar power conversion efficiency of 3.5%, showing the relevance of our approach.

Diphenilamino-substituted carbazoles were used as guest compounds for the preparation of highly efficient blue organic light-emitting diodes based on the phenomenon of delayed fluorescence. It was shown that the spectra of the delayed fluorescence of host–guest systems are identical to those of the prompt fluorescence and in general coincide with the photoluminescence spectra of the guest films. The congruence of the prompt and delayed fluorescence spectra is explained by the effective intermolecular triplet–singlet (T → S) energy transfer from the excited T states of the host to the S states of the guest molecules. High external electroluminescence efficiency of the fabricated electroluminescent devices, reaching 17%, is comparable to that achieved in phosphorescence-based organic light-emitting diodes.

Cataloged from PDF version of article. The results of an experimental study of the electroluminescent device made of ITO/CuI/2,6-di-tert-butyl-4-(2,5-diphenyl-3,4-dihydro-2H-pyrazol-3-yl)-phenol (HPhP)/3,6-Di(9-carbazolyl)-9-(2ethylhexyl) carbazole (TCz1)/Ca:Al with efficacy up to 10.63 cd/A are presented. HPhP provides blue emission with a peak wavelength at 445 nm. The layer of TCz1 acts as an electron-transporting layer. In the framework of density functional theory (DFT) approach the geometry configuration and energy levels of HPhP are found being in a good agreement with spectral and cyclic voltammogram data. (C) 2011 Elsevier B.V. All rights reserved.