An innovative concept of organic thin-film solid-state laser is proposed, with diffraction-limited output and a broad tuning range covering the visible spectrum under UV optical pumping. The laser beam is tunable over 230 nm, from 440 to 670 nm. The structure consists of a compact fixed bulk optical cavity, a polymeric intracavity etalon for wavelength tuning, as well as five different disposable glass slides coated with a dye-doped polymer film, forming a very simple and low-cost gain medium. The use of interchangeable/disposable "gain capsules" is an alternative solution to photodegradation issues, since gain chips can be replaced without realignment of the cavity.

An innovative concept of thin-film organic solid-state laser is proposed, with diffraction-limited output and a broad tuning range covering the visible spectrum under UV optical pumping. The laser beam is tunable over 230 nm, from 440 to 670 nm, with a 3 nm full width at half maximum typical spectral width. The structure consists of a compact fixed bulk optical cavity, a polymeric intracavity etalon for wavelength tuning, as well as five different disposable glass slides coated with a dye-doped polymer film, forming a very simple and low-cost gain medium. The use of interchangeable/disposable "gain capsules" is an alternative solution to photodegradation issues, since gain chips can be replaced without realignment of the cavity. The laser lifetime of a single chip in ambient conditions and without encapsulation was extrapolated to be around 107 pulses at a microjoule energy-per-pulse level.

Organic lasers offer the promise to build compact, inexpensive, broadly tunable solid-state lasers in the visible range, with potential applications in spectroscopy, bio/chemo sensing or short-haul data telecommunications. Among existing laser architectures of optically-pumped organic lasers, external-cavity resonators enable the highest conversion efficiencies, excellent beam quality, power scalability and versatility due to the open cavity. Recently, we reported on an open-cavity laser architecture using a thin film of dye-doped polymer as the gain medium, named Vertical External Cavity Surface-emitting Organic Laser (VECSOL). The very high gain of organics make these lasers highly efficient even for macroscopic cavities, even though the pulse buildup time must be short enough to fit within the gain time window defined by the pump pulse duration and the fluorescence lifetime. In this paper we analyze the laser turn-on dynamics of organic VECSELs. A simple theoretical framework is presented, based on the Statz-DeMars coupled rate equations. Simulations are compared to the experimental pulse shapes of the pump and laser beams, recorded with the same fast photodiode. We observe that the laser pulse is both shifted and broadened with respect to the 0.5-ns-long pump pulse when the cavity length is increased, together with a drop of efficiency. Efficiency curves are presented, showing a higher threshold and lower slope efficiency when the cavity length increases, which is well accounted by the model. Finally, an optimized VECSOL is presented, with a 25 ns-pulsewidth pump source, enabling reaching conversion efficiencies up to 61%.

A solid-state organic thin-film laser with intracavity frequency doubling is reported. Tunable ultraviolet emission from 309 to 322 nm is achieved from a vertical external cavity surface-emitting organic laser, with 2% efficiency (1 μJ at 315 nm). The laser comprises a poly(methyl methacrylate) layer doped with Rhodamine 640, spun-cast onto a plane mirror, a remote concave mirror, a nonlinear crystal, and a dichroic separator. The output is spectrally narrow (<0.5 nm full width at half maximum) and tunable through phase-matching selection of the fundamental radiation lasing modes. These results highlight a low-cost and portable alternative to tunable UV laser sources, useful for spectroscopic applications.

In this paper we report a detailed study of emission dynamics of an organic solid-state laser structure so-called VECSOL standing for Vertical External-Cavity Surface-emitting Organic Laser recently developed in our group. An optical-optical efficiency of 43% and 6.3% was reported for a 4-mm-long cavity incorporating 18- μ m-thick film of Poly(methyl methacrylate) (PMMA) doped with 1 wt.% of Rhodamine 640 when pumped with 7-ns-long and 0.5-ns-long pulses respectively. In order to understand the difference seen in lasing efficiency as a function of different parameters such as cavity length or pump pulse duration, Tang-Statz-deMars cavity rate equations are used to model the emission behavior in a pulsed regime. Based on this model, conversion efficiency could be optimized practically to values as high as 57%. Furthermore, some characteristics of this laser architecture such as lasing lifetime (up to 140 000 pulses at two times above lasing threshold), wavelength tuning (over 40 nm) and the system power scalability with potential operation up to mJ level are investigated.

We report on a solid-state laser structure functioning as the organic counterpart of a vertical external-cavity surface-emitting laser (VECSEL) design. The gain medium is a poly(methyl methacrylate) film doped with Rhodamine 640, spin casted onto the high-reflectivity mirror of a plano-concave resonator. Upon pumping by 7 ns pulses at 532 nm, a diffraction-limited beam (M(2)=1) was obtained, with a conversion efficiency of 43%; higher peak powers (2 kW) could be attained when resorting to shorter (0.5 ns) pump pulses. The spectrum was controlled by the thickness of the active layer playing the role of an intracavity etalon; tunability is demonstrated at over and up to 20 nm.

Light-sensitive materials as azo-polymers have interesting applications in microelectronics, biology, or energy storage, due to their capacity to change their supramolecular ordering. Light-induced modifications result in i) changes in the azobenzene-groups dipole moment due to the trans-cis isomerization, ii) thermal backward cis-trans relaxation, and iii) re-ordering of the polymer chain conformation. Conjugation of these phenomena leads to mass transport in the solid state, which is still not well understood. Changes in the surface properties of non-substituted and p-CF3,-CN,-NO2-substituted azophenoxy-polysiloxane films, before and after photo-excitation, were examined. Molecular simulations were performed to evaluate the dipole-moments of the trans and cis p-substituted azobenzene groups and provide a general vision of the spatial arrangement of polymer chains. The role of trans-cis back relaxation and that of the polymer matrix relaxation on the surface and bulk of the materials was discussed. Surface free energy determination of the non-substituted azophenoxy-polysiloxane suggested that the relaxation process is dominated by the thermal slow back-isomerization of the cis fraction and not by the motion of a glassy polymer matrix involving both the surface and bulk. A less clear situation was presented by the semi-crystalline polysiloxanes with electron-withdrawing groups substituted in the para-position. This was attributed mainly to the similar values of the dipole-moment of trans and cis azo-group, the former being slightly more dipolar than the latter.

Stimulated emission in small-molecule organic films at a high dye concentration is generally hindered by fluorescence quenching, especially in the red region of the spectrum. Here we demonstrate the achievement of high net gains (up to 50 cm-1) around 640 nm in thermally evaporated non-doped films of 4-di(4'-tert-butylbiphenyl-4-yl)amino-4'-dicyanovinylbenzene, which makes this material suitable for green-light pumped single-mode organic lasers with low threshold and superior stability. Lasing effect is demonstrated in a DBR resonator configuration, as well as under the form of random lasing at high pump intensities.

Measurements of the diffusion length L for triplet excitons in small molecular-weight organic semiconductors are commonly carried out using a technique in which a phosphorescent-doped probe layer is set in the vicinity of a supposed exciton generation zone. However, analyses commonly used to retrieve $L$ ignore microcavity effects that may induce a strong modulation of the emitted light as the position of the exciton probe is shifted. The present paper investigates in detail how this technique may be improved to obtain more accurate results for L. The example of 4,4'-bis(carbazol-9-yl)1,1'-biphenyl (CBP) is taken, for which a triplet diffusion length of L=16 +/- 4 nm (at 3 mA/cm2) is inferred from experiments. The influence of triplet-triplet annihilation, responsible for an apparent decrease of L at high current densities, is theoretically investigated, as well as the 'invasiveness' of the thin probe layer on the exciton distribution. The interplay of microcavity effects and direct recombinations is demonstrated experimentally with the archetypal trilayer structure [N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)]-4,4'-diaminobiphenyl (NPB)/CBP/ 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (named bathocuproine, BCP). It is shown that in this device holes do cross the NPB/CBP junction, without the assistance of electrons and despite the high energetic barrier imposed by the shift between the HOMO levels. The use of the variable-thickness doped layer technique in this case is then discussed. Finally, some guidelines are given for improving the measure of the diffusion length of triplet excitons in operational OLEDs, applicable to virtually any small molecular-weight material.

The stoichiometric noncovalent imprinting of pinacolyl methylphosphonate (PMP), a degradation product of a chemical warfare agent, has been investigated. A rational approach consisting of controlling the number of specific sites produced during the polymerization was carried out in order to design the methacrylic acid (MAA)-based imprinted polymers. The objective of the method was to study by NMR spectroscopy the molecular association process between the monomer (MAA) and the template (PMP) in solution. Accurate variations in the chemical shifts of H-1 and C-13 were determined in a series of samples at various concentrations in the mixture of acetonitrile/toluene (3:1, v/v). By using an elaborated data treatment, we were able to simultaneously determine the stoichiometry, the association constant, and the condensation degree of the resulting complex. On the basis of these results, a stoichiometric noncovalent PMP-imprinted polymer was subsequently synthesized. Adsorption isotherms of the materials were measured and confronted with those of an imprinted polymer conventionally synthesized with excess monomer. These results established for the first time, the feasibility of imprinted polymers with low-molecular-weight and poorly functionalized templates such as pinacolyl methylphosphonate via stoichiometric noncovalent interactions. Batch binding tests were also carried out on a series of three analogue phosphonates in order to elucidate the influence of the functionality, shape, and size of the analyte on the adsorption properties of the polymers.

The multiplication of terrorist actions in the recent events is alarming and the detection of chemical warfare agents (CWAs) has become one of the highest research priorities in the fields of security and public health. The biomimetic properties of molecularly imprinted polymers (MIPs) render them attractive for molecular recognition as well as sensing purposes. The degradation products of easily hydrolysable organophosphorus nerve agents such as pinacolyl methylphosphonate (PMP), a hydrolysis by-product of soman, are often used as templates in MIP synthesis. In this study, we describe the first example of PMP-imprinted polymer microspheres synthesized by precipitation polymerization. This one-step process involves methacrylic acid (MAA) as the monomer and divinylbenzene (DVB) as the cross-linker, in a toluene/acetonitrile mixture. Subsequent morphological characterizations of the PMP-imprinted particles show that they have diameters between 1 and 10 mum (as opposed to 4-5 mum for the non-imprinted microspheres), surface areas of up to 680 m(2) g(-1) and high porosities with pore sizes smaller than 2 nm. The present investigation also evidences the imprinting effect via batch binding experiments and reports on the use of a novel fluorescence-based methodology, where 4-methylumbelliferone (4MU) is utilised as a sensing agent to determine the PMP concentration in solution.

Although optically pumped semiconductor organic lasers have been reported for a decade, no electrically pumped organic laser diode has been till now realized. Charge-induced and triplet excited state absorption have been identified as major bottlenecks: in this context exciton dynamic plays a key role. We report on the measurement of exciton diffusion lengths in the archetypal ambipolar material CBP, in the presence of an injected current in a working multilayer device. The technique is based on moving a thin red phosphorescent layer away from the recombination zone. The amount of emitted light depends on the layer position via the diffusion of triplet excitons. We demonstrate the crucial importance of designing the structure according to optical field calculations in order to measure diffusion lengths LD. We measured a value of LD = 16 nm +/- 4 nm in CBP, and also report on the variation of LD with the injected current.

Alzheimer's disease is characterized by the presence of beta-amyloid fibril formation. The inhibition of this peptide accumulation may be a prevention method for Alzheimer's disease. Several classes of molecules have been reported to inhibit beta-amyloid fibril formation and among them carbazoles. However, very few studies have been performed to determine the destination of such molecules in vivo and especially if they can pass the blood brain barrier. The aim of this paper is to study whether carbazoles could pass the blood brain barrier, i.e. if they can circumvent ATP Binding Cassette (ABC) transporters such as P-glycoprotein (P-gp) and Multidrug Resistance-associated protein (MRP1) which efficiently limit drug brain uptake. For this purpose we have synthesized a fluorescent derivative of carbazole benzothiazolium iodide 1,2 disubstituted ethylene (referred as carbazole thiazole: CT), which can be easily detected and followed in the pre-trial study phases in cells or in tissue. We use cellular models overexpressing P-gp and MRP1. Our results show that: i) CT is able to cross membranes and to penetrate rapidly inside the cells, ii) CT is a P-gp substrate and consequently its accumulation in P-gp overexpressing cells is very low, iii) CT is a poor MRP1 substrate. In addition once inside the cells, CT rapidly binds to DNA and is then slowly reduced by intracellular reducing agents. In conclusion, the efficiency of carbazole derivatives in inhibiting the beta-amyloid formation in vivo could be highly compromised because, as P-gp substrates, they will probably not cross the blood brain barrier.

A new carbazole derivative with a 3,3′-bicarbazyl core 6,6′-substituted by dicyanovinylene groups (6,6′-bis(1-(2,2′-dicyano)vinyl)-N,N′-dioctyl-3,3′-bicarbazyl; named (OcCz2CN)2, was synthesized by carbonyl-methylene Knovenagel condensation, characterized and used as a component of multilayer organic light-emitting diodes (OLEDs). Due to its π-donor–acceptor type structure, (OcCz2CN)2 was found to emit a yellow light at λmax = 590 nm (with the CIE coordinates x = 0.51; y = 0.47) and was used either as a dopant or as an ultrathin layer in a blue-emitting matrix of 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi). DPVBi (OcCz2CN)2-doped structure exhibited, at doping ratio of 1.4 weight %, a yellowish–green light with the CIE coordinates (x = 0.31; y = 0.51), an electroluminescence efficiency ηEL = 1.3 cd/A, an external quantum efficiency ηext = 0.4 % and a luminance L = 127 cd/m2 (at 10 mA/cm2) whereas for non-doped devices utilizing the carbazolic fluorophore as a thin neat layer, a warm white with CIE coordinates (x = 0.40; y = 0.43), ηEL = 2.0 cd/A, ηext = 0.7%, L = 197 cd/m2 (at 10 mA/cm2) and a color rendering index (CRI) of 74, were obtained. Electroluminescence performances of both the doped and non-doped devices were compared with those obtained with 5,6,11,12-tetraphenylnaphtacene (rubrene) taken as a reference of highly efficient yellow emitter.

New polydimethylsiloxanes with p-substituted azobenzene side-groups were synthesized. Thin films and solutions exhibit a photochemical trans-cis isomerization of the azobenzene groups, followed by their cis-trans thermal relaxation in the dark. In films, relaxation rates were found to be 100-1000 times slower than the rates of photoisomerization, the former being very sensitive to the electron-acceptor character of the sustituents. in solution, the rates of cis-trans relaxation are lower than those obtained for the solid state. This is ascribed to the dipolar intramolecular interactions between cis chromophores, which are favored in solution.

Bright blue organic light-emitting diodes (OLEDs) based on 1, 4, 5, 8, N-pentamethylcarbazole (PMC) and on dimer of N-ethylcarbazole (N, N′-diethyl-3, 3′-bicarbazyl) (DEC) as emitting layers or as dopants in a 4, 4′-bis(2, 2′-diphenylvinyl)-1, 1′-biphenyl (DPVBi) matrix are described. Pure blue light with the CIE coordinates (x = 0.153, y = 0.100), electroluminescence efficiency ηEL of 0.4 cd A−1, external quantum efficiency ηext of 0.6% and luminance L of 236 cd m−2 (at 60 mA cm−2) were obtained with PMC as an emitter and the 2, 9-dimethyl-4, 7-diphenyl-1, 10-phenantroline (BCP) as a hole-blocking material in five-layer emitting devices. The highest efficiencies ηEL of 4.7 cd A−1 and ηext = 3.3% were obtained with a four-layer structure and a DPVBi DEC-doped active layer (CIE coordinates x = 0.158, y = 0.169, λpeak = 456 nm). The ηext value is one the highest reported at this wavelength for blue OLEDs and is related to an internal quantum efficiency up to 20%.