Nonlinear Optical Activity of a Chiral Organic-Inorganic ([(NH3CH2CH2)3NH])2[MnBr5]Br5 Photoluminescent and Piezoelectric Crystal.

The family of Mn-based organic-inorganic hybrids has greatly expanded due to their advantages in applications. They also show superior bright and size-tunable photoluminescence and can be considered a perfect alternative to toxic lead-based compounds. In this work, we present the detailed structural, optical, and electrical characterization of ([(NH3CH2CH2)3NH])2[MnBr5]Br5. The title compound exhibits a unique type of inorganic arrangement created by the trigonal bipyramids. It crystallizes in noncentrosymmetric space group R32, indicating its optical activity, piezoelectricity, and second-order optical nonlinearity proven by the second harmonic of light measurements. The studied crystals exhibit intense photoluminescence originating from the Mn(II) ion 4T1(G) → 6A1 transition. The measured lifetime of the photoluminescence emission is ≤1.5 ms, while the measured quantum yield for both powder and crystal samples reaches ∼70%.

Optically Controlled Development of a Waveguide from a Reservoir of Microparticles.

Light can be guided without diffraction in prefabricated structures: optical fibers and waveguides or in actively created spatial solitons in optically nonlinear media. Here, an approach in which a self-stabilized optical waveguide develops from a reservoir of building blocks-spherical polymer microparticles (MPs)-and is pushed through an optically passive medium-water-is presented. The optical waveguide, formed by a chain of these microparticles and one microsphere wide, is self-stabilized and propelled by the guided light, while its geometrical and dynamical properties depend on the diameter-to-wavelength ratio. The smallest investigated particles, 500 nm in diameter, form single-mode waveguides up to tens of micrometers long, with the length limited only by optical losses. In contrast, waveguides constructed of larger MPs, 1 and 2.5 µm in diameter, are limited in length to only a few particles due to interference of different modes and beating of light intensity.

First-order hyperpolarizabilities of propellanes: elucidating structure-property relationships.

Following recent experimental work demonstrating strong nonlinear optical properties, namely second harmonic generation of light, in crystals composed of 16,20-dinitro-(3,4,8,9)-dibenzo-2,7-dioxa-5,10-diaza[4.4.4]propellane molecules [A. Miniewicz, S. Bartkiewicz, E. Wojaczynska, T. Galica, R. Zalesny and R. Jakubas, J. Mater. Chem. C, 2019, 7, 1255-1262] in this paper we aim to investigate "structure-property" relationships for a series of 16 propellanes presenting a wide palette of substituents with varying electron-accepting/donating capabilities. To that end, we use electronic- and vibrational-structure theories and a recently developed generalized few-state model combined with a range-separated CAM-B3LYP functional to analyze electronic and vibrational contributions to the first hyperpolarizability for the whole series of molecules. The variations in computed properties are large among the studied set of substituents and can reach an order of magnitude. It has been demonstrated that the maximum values of frequency-independent first hyperpolarizability are expected for strong electron-accepting NO2 substituents, but only at the preferred position with respect to the electronegative oxygen atom in the 1,4-oxazine moiety. This holds for electronic as well as vibrational counterparts.

Organic Nanocrystal Fabrication Using the Process of Resonant Second-Harmonic Generation of Light.

Laser ablation with the use of ultra-short laser pulses is a widely used technique for the fabrication of nanoparticles of metals, inorganic and hybrid materials. However, fabrication of fragile organic nanocrystals via laser ablation is rarely used due to easy photodegradation of molecules. The method employing laser irradiation of the target material is beneficial as no other chemicals are used in the production of nanoparticles, except for a given material and a solvent. In this work, we test the concept of formation of nonlinear optical (NLO) organic nanocrystals dispersion in water by irradiation of the microcrystals of the NLO material with nonabsorbed infrared nanosecond light pulses. These pulses, due to a nonlinear optical process active in a noncentrosymmetric organic crystal, such as those studied in this work, DCNP dye (3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole), produce nanosecond pulses of second-harmonic (SH) light. Due to doubling of photon energy, they are reabsorbed in the volume of DCNP microcrystals and thermal shocks fracture them into nanometer size crystals. To the best of our knowledge, such process and its interpretation have not been described yet in the literature.

Thermocapillary Marangoni Flows in Azopolymers.

It is well known that light-induced multiple trans-cis-trans photoisomerizations of azobenzene derivatives attached to various matrices (polymeric, liquid crystalline polymers) result in polymer mass movement leading to generation of surface reliefs. The reliefs can be produced at small as well as at large light intensities. When linearly polarized light is used in the process, directional photo-induced molecular orientation of the azo molecules occurs, which leads to the generation of optical anisotropy in the system, providing that thermal effects are negligible. On the other hand, large reliefs are observed at relatively strong laser intensities when the optofluidization process is particularly effective. In this article, we describe the competitive thermocapillary Marangoni effect of polymer mass motion. We experimentally prove that the Marangoni effect occurs simultaneously with the optofluidization process. It destroys the orientation of the azopolymer molecules and results in cancelation of the photo-induced birefringence. Our experimental observations of polymer surface topography with atomic force microscopy are supported by suitable modelings.

Investigations of organic-inorganic hybrids based on homopiperidinium cation with haloantimonates(iii) and halobismuthates(iii). Crystal structures, reversible phase transitions, semiconducting and molecular dynamic properties.

A description of the thermal, structural, 1H NMR, electric and optical properties of four organic-inorganic hybrids, haloantimonates(iii) and halobismuthates(iii), based on homopiperidinium cation: (C6H14N)2SbCl5 (abbrev. HSC), (C6H14N)2SbBr5 (HSB), (C6H14N)2BiCl6[H3O] (HBC), (C6H14N)2BiBr5 (HBB), is presented. The common feature of the crystal structures of the studied compounds is the 1D (one-dimensional) chain for the anionic network in HSC, HSB and HBB, 1D hydrogen bond chain between 0D (zero-dimensional, isolated) BiCl6 octahedrons and hydronium moieties in HBC as well as a rich polymorphism in the solid state for all title compounds. The structures of the Sb(iii) and Bi(iii) derivatives are not isomorphous and they crystallize in the following space groups: HSC in P212121 both at 280 and 150 K, HSB in Pmna and P212121 at 310 and 150 K, respectively, HBC in C2/m, C2/m and C2/c at 300, 260 and 200 K, respectively, and HBB in P21/n both at 280 and 200 K. The anionic networks are in the forms of either pseudo- and zig-zag chains or a chain of a hydrogen bond. The band gap values, using the Tauc plot as well as the ac and dc conductivity parameters, were estimated. On the basis of the 1H NMR spin-lattice relaxation times, T1, and second-moment, M2, measurements and the dielectric responses, the molecular mechanisms of the phase transitions (PTs) have been postulated. The structural PTs are discussed in terms of the changes in cationic dynamics and distortions of the anionic sublattice. The powder technique of SHG (Kurtz and Perry method) has been used to analyze the second-order nonlinear optical properties of HSC.

Kinetics of thermal cis-trans isomerization in a phototropic azobenzene-based single-component liquid crystal in its nematic and isotropic phases.

Single-component azobenzene-based phototropic liquid crystals (PtLC) are promising materials that have started to be explored for photonic applications. One of the essential factors determining the applicability of these materials is the rate of the thermally driven cis-trans isomerization. In this paper, the kinetics of the thermal back cis-to-trans reaction in a pure 4-hexyl-4'-methoxyazobenzene (6-AB-O1) compound in its isotropic liquid and nematic phases is studied (the undoped LC). The reaction rate constants, activation energies and thermal activation parameters were determined based on spectroscopic studies. The reaction kinetics is compared to that measured for the compound dissolved in chloroform. The results demonstrate that the thermal back reaction depends on the phase and molecular environment of the cis-isomer. Moreover, the effect of temperature on the absorption spectra of 6-AB-O1 in its isotropic, nematic and crystalline phases is examined. The changes in the compound's absorption spectra in the respective phases have been correlated to the positional order parameter S.

Enlargement of the organic solid-state DFB laser wavelength tuning range by the use of two complementary luminescent dyes doped into the host matrix.

The spectral tuning range of dye lasers is closely associated with the gain profile provided by the utilized luminescent compound. Here, we present the results of studies aimed at broadening the wavelength tuning range in distributed feedback (DFB) lasers, made up of polymeric layers doped with a mixture of two complementary dyes. We have used the 3-(2,2-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) luminescent dye, showing stimulated emission in its crystalline form, and the Rhodamine 700 (Rh700) laser dye, which is red-shifted in luminescence relative to DCNP, both doped into a poly(methyl methacrylate) (PMMA) host matrix. We have investigated the relationships between the additives' relative weight to weight ratios and their ability to exhibit a nonradiative energy transfer process that is inherent with a luminescence quenching of the shorter wavelength emitter, the so-called donor. This in turn directly reflects the efficiency of simultaneous utilization of both dyes' emission bands for lasing. By the proper engineering of the gain material composition, it was possible to broaden the DFB lasing tuning spectral range up to 125 nm, which is twice as much compared to the DCNP/PMMA material, i.e. without addition of Rh700. Finally, the presented results have shown that additional random feedback, which is detrimental to the DFB lasing, originating from the presence of DCNP crystals within the polymeric bulk, can be effectively suppressed by the superposition of a temporary DFB resonator.

Environment-Sensitive Behavior of DCNP in Solvents with Different Viscosity, Polarity and Proticity.

A pyrazoline derivative, 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP), is studied by using optical spectroscopy methods in several solvents at room and at low temperatures. The DCNP molecule reveals a complex photophysics behavior, which is sensitive to solvent polarity, proticity, temperature and viscosity and arises from the presence of two rotational degrees of freedom of the dicyanovinyl group--the torsion around the double C=C bond and the s-trans-s-cis isomerization around the single C-C bond--that differently behave in various environmental conditions. The fluorescence yield of a few percent and sub-nanosecond decay times observed at room temperature make the compound useful for optical studies of liquid environments. The proticity of polar solvents can be detected with two-exponential fluorescence decays. At low temperatures, DCNP can be used as solvent viscosity or temperature fluorescent sensor.

First principle calculations of the electronic and vibrational properties of the 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole molecule.

Results of first principle quantum chemical calculations of electronic and vibrational properties of the push-pull 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) molecule are reported and discussed. The structure of DCNP was optimized with HF/6-311G methodology and found to be planar. On the basis of obtained geometry, infrared absorption and Raman spectra were computed within the HF/6-311++G** formalism. They allow to conclude that the changes of molecule dipole moment and variation of its polarizability appear at the same vibrational mode and affect the optical properties of the DCNP. Four different methodologies: time-dependent HF and time-dependent DFT method with B3LYP, LC-BLYP, and CAM-B3LYP potentials were used to compute the optical absorption spectra of DCNP. Influence of solvent on molecular electronic structure was studied within the C-PCM model. It predicts the DFT/B3LYP methodology as the best one to compute the NLO properties of the DCNP. The computed HOMO and LUMO orbitals show evidence that the ground state of the molecule is located at its aromatic part. The discussion of charge transfer during the excitation process for the transition S0-S1 was performed. The charge transfer parameter calculated in vacuum and in solvent gives the evidence that the solvent environment weakly enhance the molecular charge transfer. It confirms the tendency of an occurrence of the intermolecular charge transfer in DCNP which is crucial for its hyperpolarizability magnitude. It was proved that the second-order susceptibility corresponding to SHG may be calculated for host-guest polymer/DCNP composite using the simple oriented gas model and the rigorous local field approach should not necessarily be applied.

[NH2(C2H4)2O]MX5: a new family of morpholinium nonlinear optical materials among halogenoantimonate(III) and halogenobismuthate(III) compounds. Structural characterization, dielectric and piezoelectric properties.

This paper presents the structural features of ionic complexes formed by morpholine and metal ions which belong to group VA, namely Sb(III) and Bi(III). A series of target inorganic-organic hybrid compounds of the general formula [NH(2)(C(2)H(4))(2)O](2)MX(5) (where M = Sb, Bi; X = Cl, Br) has been synthesized by incorporating the organic component (morpholine) into the highly polarizable one-dimensional halogenoantimonate(III)/halogenobismuthate(III) chain network. Among the studied compounds, four were found to crystallize in the room temperature phase in the piezoelectric, orthorhombic space group P2(1)2(1)2(1), Z = 4, the feature being confirmed by the powder second harmonic generation of light and piezoelectric measurements. Dielectric dispersion studies between 200 Hz and 2 MHz disclosed a relaxation process below room temperature well described by the Cole-Cole equation. Based on crystal structures available in Cambridge Structural Database (version 5.32, November 2010) we attempt to show a relationship between the acentric symmetry of compounds and the type of anionic network within the R(2)MX(5)-subgroup (where R denotes organic cation) of halogenoantimonates(III) and halogenobismuthates(III).

Surface Plasmon Polariton Excitation in Metallic Layer Via Surface Relief Gratings in Photoactive Polymer Studied by the Finite-Difference Time-Domain Method.

We performed numerical investigations of surface plasmon excitation and propagation in structures made of a photochromic polymer layer deposited over a metal surface using the finite-difference time-domain method. We investigated the process of light coupling into surface plasmon polariton excitation using surface relief gratings formed on the top of a polymer layer and compared it with the coupling via rectangular ridges grating made directly in the metal layer. We also performed preliminary studies on the influence of refractive index change of photochromic polymer on surface plasmon polariton propagation conditions.

Single- and two-photon excited fluorescence in organic nonlinear optical single crystal 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole.

Fluorescence of nonlinear optical organic single crystal of 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (DCNP) excited by a nonabsorbed light pulses from Q-switched Nd:YAG laser λ = 1064 nm as well as absorbed λ = 532 nm light is reported. Two mechanisms of two-photon excited fluorescence are considered: (i) direct two-photon excited fluorescence and (ii) single-photon excitation due to reabsorption of light generated in process of second harmonic generation (SHG) by the crystal due to its nonlinear optical properties. Strong anisotropy of fluorescence that has been observed is linked with uniaxial molecular alignment. Fluorescence decay profile shows two- exponential decay with lifetimes of emitting species of 3.7 and 5.6 ns at 293 K. The excitation and fluorescence spectra of the DCNP single crystal have been measured at 294 K and in function of temperature down to 77.4 K. The strong bathochromic shift of fluorescence spectrum in crystal with respect to fluorescence of DCNP molecule in solution is observed and interpreted with possible formation of molecular aggregates.

Polarization dependence of holographic grating recording in azobenzene-functionalized polymers monitored by visible and infrared light.

The holographic grating recording process in thin films of amorphous azobenzene-functionalized polymers has been widely reported in the literature. In spite of the many reports, little is known about the mechanisms responsible for different temporal behaviors of the diffraction efficiency during long recording times. Here, we report on experimental studies of the diffraction efficiency changes during the holographic diffraction grating recording process in photochromic polymer. The gratings were inscribed for four different polarization combinations of the recording beams: s-s, p-p, s-p and right to left circular polarization (RCP-LCP) employing the degenerate two-wave mixing technique. The grating recording process was simultaneously monitored by three different wavelengths: 514.5 nm (writing) and 632.8 and 904 nm (reading). The temporal evolution of the diffraction efficiency (for all polarization configurations and for each wavelengths) was precisely fitted within the model, which assumes simultaneous formation of the absorption grating and three coupling phase gratings shifted by 0 or pi with respect to each other. Two of the phase gratings originate from the refractive index grating changes in the bulk (volume) of a material and the third one from the surface relief modulation. The model enabled us to extract relevant parameters for each grating such as the build-up time constant, its final amplitude, and the phase shifts between phase gratings. Performed studies and the discussion of results revealed the main differences in the diffraction grating formation process for s-s, p-p, s-p, and RCP-LCP polarization configurations.

Synthesis, characterization, and study of photoinduced optical anisotropy in polyimides containing side azobenzene units.

In this paper, novel processable aromatic polymers with imide rings and attached as side-chain azobenzene units are presented. Polymers differ in the chemical structures of chromophores and polymer backbones. Azopolymers were obtained by a two-step synthetic approach. This includes the preparation of a precursor poly(esterimide) and poly(etherimide) with pendant phenolic hydroxyl groups, followed by the covalent bonding of NLO chromophores onto the polyimide backbone by the Mitsunobu reaction. The degree of functionalization of polymers was estimated by UV-vis spectroscopy. Polymers were characterized and evaluated by FT-IR, (1)H NMR, X-ray, UV-vis, DSC, and TGA methods. The synthesized polymers exhibited glass transition temperatures in the range of 167-228 degrees C, thermal stability with decomposition temperatures in the range of 275-446 degrees C, and excellent solubilities in common organic solvents. The light-induced optical anisotropy was studied in obtained azopolymers with the help of a holographic grating recording technique. Two polarization geometries were applied for the grating inscription s-s and p-p. The influence of the polarization geometry on the diffraction efficiency dynamics and on the depth of the surface modulation was not observed, which is different from results reported in the literature. Surface relief gratings, which appeared after the light exposure, were observed by atomic force microscopy. Additionally, the optical anisotropy in poly(esterimide)s was investigated by photoinduced birefringence measurements. For the first time, in polyimide with covalently bonded azobenzene derivatives, the high photoinduced birefringence (Delta n = 0.01) was measured.

Biopolymer-based material used in optical image correlation.

We investigate the possible application of a modified deoxyribonucleic acid (DNA)-dye system for dynamic processing of optical information, e.g., optical correlation. The system consists of a biopolymeric matrix made of DNA substituted with the cationic surfactant molecule cetyltrimethyl-ammonium chloride (CTMA) and doped with a photochromic Disperse Red 1 dye. Fast dynamics (millisecond range of rise and fall times) of output correlation signal formation was measured in a joint Fourier transform optical correlator experimental setup. Full reversibility of the correlation signal and reproducibility were observed even after long-time exposures.

On the inscription of period and half-period surface relief gratings in azobenzene-functionalized polymers.

Laser-light-induced surface relief grating inscription was carried out in the newly synthesized azobenzene-functionalized poly(amide-imide)s having the same main- and side-chain structures but different substituents in the azobenzene groups. The gratings were inscribed employing the two-wave mixing technique with linearly polarized laser beams. Three different polarization configurations were used: s-s, p-p, and s-p. The relatively deep surface relief gratings of period Lambda were formed for the case of s-s and p-p polarizations, whereas the s-p inscription resulted in the half-period grating (Lambda/2) with the weak surface modulation. The origin of the formation of Lambda/2 structure for s-p configuration results from the interference between zeroth- and first-order beams scattered on the polarization refractive index grating and having the same polarization. On the basis of this idea, we presented the simple kinetic model predicting and modeling the half-period grating formation with its temporal evolution. The proposed model is consistent with the experimental findings.

Analysis of the kinetics of diffraction efficiency during the holographic grating recording in azobenzene functionalized polymers.

The laser-assisted holographic grating recording process in films of azobenzene functionalized polymers is usually studied by observation of the efficiency of light scattering on a developing in time diffraction grating. Various possible mechanisms contributing to grating formation as well as the bulk or surface origin (bulk refractive index and/or relief grating) of light scattering make the analysis of kinetics of grating recording, from the light scattering data only, difficult and ambiguous. To fully explain experimentally observed various and complex (frequently nonexponential) kinetics of the first-order light diffraction intensity, we considered a simple single-exponential growth of the two phase gratings in the same polymer film. In modeling we assumed that the bulk refractive index grating Deltan(t) and the surface relief grating Deltad(t) differ considerably in their growth rates and we allowed for a nonstationary phase shift Deltaphi(t) between them which was experimentally observed during the recording process. The origin of the nonstationary phase shift is a result of a slow shift of interference pattern due to delicate symmetry breaking in illumination conditions (e.g., difference in beam intensities and deviation of exact symmetrical beam incidence angles on the sample). Changing only such parameters as stationary amplitudes of refractive index and relief gratings for a span of phase shifts (0-pi) between them, we obtained a series of kinetic responses which we discuss and interpret. The various examples of temporal evolution of diffraction efficiency for the same grating formation kinetics, modeled in our work, supply evidence that great care must be taken to properly interpret the experimental results.