The development of high-efficiency near-infrared (NIR) emitters for organic light-emitting diodes (OLEDs) and organic semiconductor lasers has become an important target in organic photonics. Herein, it is demonstrated that donor-acceptor-donor borondifluoride curcuminoid derivatives represent a versatile and simple platform for the molecular engineering of high-efficiency NIR emitters combining thermally-activated delayed fluorescence (TADF) with excellent electroluminescence properties and amplified spontaneous emission (ASE) activity. A series of donor-acceptor-donor curcuminoid compounds containing triphenylamino-substituents for the donor side groups and various acceptor units in the meso position were designed and synthesized. The investigation of the effects of the molecular structure on the TADF properties show that the nature of the substituents enables a fine tuning of the emission wavelengths while maintaining high photoluminescence quantum yield values. These NIR TADF dyes were used in OLEDs with an external quantum efficiency of almost 1% for a maximum emission wavelength of 797 nm. They also show a low threshold tuneable amplified spontaneous emission between 725 and 900 nm. Overall, this study provides new essential insights to rationalize the TADF activity of this family of NIR emitters and offers important prospects for designing the next generation of NIR TADF-OLEDs and organic semiconductor laser materials.

We utilized a metal propionate solution to prepare polycrystalline bismuth-substituted yttrium iron garnets through the metal-organic decomposition process. After conducting thorough optimization, we successfully synthesized a garnet that exhibited a high magneto-optic response directly at the end of an optical fiber. A notable achievement of our work lies in the ability to restrict the size and position of the garnet to match the dimensions of the fiber's core. The functionalized fiber was integrated into a magneto-optical sensor setup, offering the flexibility to operate either in the Faraday rotation or magnetic circular dichroism mode.

We show that through the introduction of short dimethylsiloxane chains, it was possible to suppress the crystalline state of CBP in favor of various types of organization, transitioning from a soft crystal to a fluid liquid crystal mesophase, then to a liquid state. Characterized by X-ray scattering, all organizations reveal a similar layered configuration in which layers of edge-on lying CBP cores alternate with siloxane. The difference between all CBP organizations essentially lay on the regularity of the molecular packing that modulates the interactions of neighboring conjugated cores. As a result, the materials show quite different thin film absorption and emission properties, which could be correlated to the features of the chemical architectures and the molecular organizations.

We report herein the synthesis of siloxane-functionalized CBP molecules (4,4′-bis(carbazole)-1,1′-biphenyl) for liquid optoelectronic applications. The room-temperature liquid state is obtained through a convenient functionalization of the molecules with heptamethyltrisiloxane chains via hydrosilylation of alkenyl spacers. The synthesis comprises screening of metal-catalyzed methodologies to introduce alkenyl linkers into carbazoles (Stille and Suzuki Miyaura cross-couplings), incorporate the alkenylcarbazoles to dihalobiphenyls (Ullmann coupling), and finally introduce the siloxane chains. The used conditions allowed the synthesis of the target compounds, despite the high reactivity of the alkenyl moieties bound to π-conjugated systems toward undesired side reactions such as polymerization, isomerization, and hydrogenation. The features of these solvent-free liquid CBP derivatives make them potentially interesting for fluidic optoelectronic applications.

Excitation of electrons into higher energy states in solid state materials can be induced by absorption of visible light, a physical process generally studied by optical absorption spectroscopy. A promising approach for improving the spatial resolution of optical absorption spectroscopy beyond the diffraction limit is the detection of photoinduced forces by an atomic force microscope operating under wavelength-dependent light irradiation. Here, we report on a combined photovoltaic/photothermal effect induced by the absorption of visible light by the microscope probes. By monitoring the photoinduced modifications of the oscillation of the probes, it is found that the oscillation phase-voltage parabolic signals display specific fingerprints which depend on light intensity and the nature of the materials composing the probes. In particular, a localized surface photovoltage (SPV) is evidenced at the tip apex of uncoated Si probes, while none is observed on Au-coated Si probes. The photothermal effects are distinguished from photovoltaic effects by specific shifts of the phase-voltage parabolas. The findings are relevant for the whole range of atomic force microscopy techniques making use of visible light as an additional means of local optical characterization.

We have studied the magnetic properties of various Boron particles obtained by different methods and have found evidence of soft ferromagnetism in all. While our study cannot unequivocally exclude that Boron is at the origin of the magnetism, we suggest that various impurities which are either the result of the synthetic process or come from the intentional doping of the Boron particles are indeed responsible for the observed magnetic properties. The phenomenon bears similarities with what is observed in magnetic oxides such as MgO or ZnO.

Epsilon-near-zero (ENZ) properties have been reported in organic molecular films. In particular, cyanine and squaraine films have been shown to exhibit ENZ properties in the visible spectral region with a strong 3(rd) order nonlinear optical response near the ENZ spectral region. Noting both cyanine and squaraine belong to the polymethine family, a series of six curcuminoid borondifluoride (Curc) derivatives were developed to examine whether such a polymethine character is positively correlated with the ENZ property of the organic films. Those Curc derivatives possess a Donor-Acceptor-Donor (D-A-D) architecture with acceptor, AcacBF(2), located at the molecular center. The backbone of Curc is designed such that the donor strength can be tuned to transit between charge transfer (CT) and polymethine character. This balance between CT and polymethine character of the Curc series is examined based on the Lippert-Mataga plot. As donor strength in the D-A-D structure increases, CT character is less marked resulting in a more dominant polymethine character. The structural and optical properties of the Curc films with a thickness in the order of 30 nm were examined to correlate the polymethine character with the ENZ response. The results obtained in isotropic Curc thin films demonstrate that an increase of polymethine character associated with a stronger donor strength leads to an appearance/enhancement of the ENZ property in the visible spectrum range from 500 to 670 nm. Overall, this study provides useful guidelines to engineer new organic materials showing ENZ properties in a desired spectral range.

We present a specific near-field configuration where an electrostatic force gradient is found to strongly enhance the optomechanical driving of an atomic force microscope cantilever sensor. It is shown that incident photons generate a photothermal effect that couples with electrostatic fields even at tip-surface separations as large as several wavelengths, dominating the cantilever dynamics. The effect is the result of resonant phenomena where the photothermal-induced parametric driving acts conjointly (or against, depending on electric field direction) with a photovoltage generation in the cantilever. The results are achieved experimentally in an atomic force microscope operating in vacuum and explained theoretically through numerical simulations of the equation of motion of the cantilever. Intrinsic electrostatic effects arising from the electronic work-function difference of tip and surface are also highlighted. The findings are readily relevant for other optomicromechanical systems where electrostatic force gradients can be implemented.

Different bismuth-substituted yttrium iron garnet thin films were prepared on silica substrates by metal organic decomposition of propionic salts with varied initial amounts of bismuth, annealing time, and temperature. The magneto-optical properties were monitored continuously during the annealing step, yielding access to the activation energy of the garnet film crystallization. These measurements coupled with X-ray diffraction spectra of the final products show that the magneto-optical properties of the films deposited on silica are limited by the saturation of bismuth substitution and appearance of side products with high initial bismuth contents.

The capability to control charge transfer dynamics in a donor-acceptor molecule is important for efficient optoelectronic devices. Charge transfer dynamics is governed by thermodynamics of donor-acceptor charges in a given dielectric environment. Metamaterial structure has been shown to be able to control charge separation and charge recombination processes via nonlocal effect on dielectric permittivity for a fixed donor-acceptor distance organic film. Here, we report the influence of the metamaterial structure on the donor-acceptor distance dependence of the electron transfer process occurring in liquid crystalline organic semiconductor thin films. By examining the charge recombination rate in three different donor-acceptor distances, it is found that the barrier height beta increases from 0.084 to 0.137 angstrom(-1) by 63% in the presence of metal-dielectric multilayered metamaterial structures. Based on the Marcus theory on the charge transfer process, we show that a further increase in the driving force for a larger donor-acceptor distance is mainly responsible for the barrier height increase in the presence of a multilayered metamaterial substrate when compared with a glass substrate. This study will provide a significant step forward in enabling more efficient hybrid organic-optoelectronic devices associated with the charge transfer process.

We report a novel approach to modify the second order nonlinear optical (NLO) susceptibility of organic nanofiber crystals by hybridization with the optical modes of microcavities in the strong coupling regime. The wavelength dependence of the SHG efficiency displays two intense peaks corresponding to the so-formed light-matter hybrid states. Our results demonstrate an enhancement of the resonant SHG efficiency of the lower polariton by 2 orders of magnitude for the collectively coupled molecules as compared to that of the same material outside the microcavity. This study is a proof of principle that opens a new direction for NLO of organic materials in subwavelength resonators.

We investigate the photophysical properties of organic donor-acceptor dyad and triad molecular systems based on triphenylene and perylene diimide units linked by a non-conjugated flexible bridge in solution using complementary optical spectroscopy techniques. When these molecules are diluted in dichloromethane solution, energy transfer from the triphenylene to the perylene diimide excited moieties is evidenced by time-resolved fluorescence measurements resulting in a quenching of the emission from the triphenylene moieties. Simultaneously, another quenching process that affects the emission from both donor and acceptor units is observed. Solution ultrafast transient absorption measurements provide evidence of photo-induced charge transfer from either the donor or the acceptor depending upon the excitation. Overall, the analysis of the detailed time-resolved spectroscopic measurements carried out in the dyad and triad systems as well as in the triphenylene and perylene diimide units alone provides useful information both to better understand the relations between energy and charge transfer processes with molecular structures, and for the design of future functional dyad and triad architectures based on donor and acceptor moieties for organic optoelectronic applications.

Plasmonic nanostructures have recently been shown to alter the photonic density of states and to provide opportunities to control semiconductor photophysical properties.1-4 Experimentally and theoretically,5 we investigated the effects of a range of hyperbolic metamaterial (HMM) lamellar structures consisting of metal and dielectric multilayers on the photoluminescence (PL) lifetime of several organic chromophores which emission range from UV to visible. These molecules were immersed in a polymeric matrix spin-coated on top of the HMM substrates and streak camera measurements were completed to monitor the evolution of the chromophores spontaneous emission. The ratio of the PL lifetimes of chromophores located on top of HMM nanostructures and on top of fused silica was shown to vary in a non-monotonous way. We then showed that normalized PL lifetime of the chromophore strongly depends on the HMM phase and the number of metal-dielectric pairs. To analyze systematically this behavior and fully understand the involved mechanisms, we also developed a theoretical analysis and took advantage of both invariant imbedding method and FDTD simulation as computational tools to quantitatively explain the experimental results and predict the responses, which could be observed when varying further the HMM nanostructures. 1. M. A. Noginov, et al., Opt. Lett., 2010, 35, 1863. 2. T. U. Tumkur, , et al., Appl. Phys. Lett., 2012, 100, 161103. 3. P. Shekhar, , et al., Phys. Rev. B, 2014, 90, 045313. 4. H. N. Krishnamoorthy, , et al., Science, 2012, 336, 205. 5. K. J. Lee, , et al. In preparation, 2016.

Department of Physics, CNRS-Ewha Intern University, Seoul 120-750, Korea. E-mail: ri Center for Length, Division of Physical Standards and Science (KRISS), 267 Gaj South Korea Sorbonne Universités, UPMC Univ Paris Moléculaire, UMR 8232, Chimie des Pol France. E-mail: fabrice.mathevet@upmc.fr Advanced Materials Engineering and Model and Technology, 50-370 Wroclaw, Poland Institut de Physique et Chimie des Matéri Université de Strasbourg, 23 Rue du Loess, Aix Marseille Université, CNRS, CINaM UM 13288 Marseille, France Elements Chemistry Laboratory, RIKEN, W riken.jp † Contributed equally to this work. ‡ Present Address: Center for Organic (OPERA), Kyushu University, Fukuoka, Jap Cite this: RSC Adv., 2016, 6, 57811

Dynamics of the photo-induced charge transfer are correlated with the structural properties of self-assembled discotic donor–acceptor dyad and triad films.

Highly fluorescent non-volatile fluidic fluorene derivatives functionalized with siloxane chains were synthesized and used in monolithic solvent-free liquid organic semiconductor distributed feedback lasers. The photoluminescence quantum yield values, the amplified spontaneous emission thresholds and the ambipolar charge carrier mobilities demonstrate that this class of materials is extremely promising for organic fluidic light-emitting and lasing devices.

We present experimental and theoretical study of the interaction of Light Induced Self-Written (LISW) waveguides in photopolymers. We show that the diffusion of the monomer controls the refractive index distribution. Consequently it influences the interaction between the LISW channels allowing the observation of anti-crossing behavior or the propagation of an array of non interacting LISW waveguides.

Sixteen model (donor–π–)2acceptor–π–donor [(D–π–)2A–π–D] molecules with an extraordinary T-shaped arrangement were designed and synthesized. Indan-1,3-dione was employed as a central acceptor with electron donors linked at the C-2, C-4, and C-7 positions. These push–pull molecules represent a first systematic modification of an indan-1,3-dione-fused benzene ring. The structures and properties of all target molecules were investigated by X-ray analysis, electrochemistry, UV/Vis absorption spectroscopy, differential scanning calorimetry, electric-field-induced second-harmonic generation (EFISHG) studies, and DFT calculations. A thorough evaluation of all of the gathered data has been performed, and structure–property relationships were evaluated. Electron donors attached at the C-2 position through π systems of various lengths affect the studied properties most significantly. The side donors at C-4 and C-7 can be described as auxiliary and do not dominate the observed properties. However, thiophene is a more efficient donor than N,N-dimethylaniline in this respect. Hence, indan-1,3-dione bearing a piperidylthiophene donor connected through a propenylidene spacer at C-2 completed with two side thiophen-2-ylethynyl branches at C-4 and C-7 showed the highest figure of merit among the studied properties.

Sum-frequency generation from chiral bulk media holds the promise of a powerful tool in the investigation of biological as well as artificial materials containing optically active elements. Since this technique is based on a nonlinear optical effect, the high intensities of the illuminating light sources may induce spurious artifacts. Using simple conjugated chromophores, we demonstrate that multi-photon induced irreversible photolysis may be avoided while keeping undiminished levels of sum-frequency signals. In addition we show that the concurrent multi-photon induced luminescence may provide complementary means of imaging samples. (C) 2015 Published by Elsevier B.V.