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Novel nonlinear optical (NLO) molecules are designed in order to meet their tremendous demand in the field of optics and electronics. The first attempt of the structural tailoring of disperse orange 3 (DO3)-an azodye is made to develop nineteen derivative molecules (D1-D19). Two approaches were opted for preparing 4 groups of molecules. The first one was the extension of $\pi$-conjugated system and the second strategy was the use of diverse electron donor and acceptor groups to develop unique donor-$\pi$-acceptor systems. Density functional theory (DFT) calculations were performed for in silico characterization of the studied molecules. The polarizability (${\alpha }_o$) and first-order hyperpolarizability (${\beta }_o$) values gave the insight of nonlinear optical response. All the designed molecules with extended conjugation and unique electron donor and acceptor group combination showed remarkably high ${\alpha }_o$ and ${\beta }_o$ values. The highest hyperpolarizability value (42477.48 a.u.) with several thousand increases than ${\beta }_o$ (7113.25 a.u.) of reference DO3, was depicted by D19 of the designed derivatives. This can be attributed to greater intramolecular charge transfer (ICT) in it. Various interaction studies were made and global reactivity descriptors (GRDs) were calculated to determine their chemical nature and stability. The outcome of our study suggests that the designed molecules are potential candidates for NLO applications, like energy conversion for producing tunable lasers and high-resolution spectroscopic studies.

With the rapid development of intelligent materials in recent years, intelligent hydrophobic materials have become a new research direction, and hydrophobic surfaces with adjustable wettability have enormous application potential in many fields. Generally speaking, surface wettability is determined by the combined effect of surface chemical composition and surface morphology. Therefore, the photoresponsive wettability of azobenzene-modified surfaces can be achieved by constructing rough surface of micro-nano scale and reducing the surface free energy. In this paper, we synthesized two photo responsive hydrophobic azobenzene derivatives (AAAB-PFDT and UAAB-PFDT), characterized their structure, thermal degradation behavior, and microscopic morphology. The light conversion performance of the two materials in dispersion was also studied using a UV–Vis spectrometer. By depositing the materials on the glass slide, the measurements of the water contact angle (WCA) under different lighting conditions were performed, demonstrating that both materials exhibit excellent photoswitchable hydrophobicity and reversibility.

Nonlinear refraction in a new polymer material based on diglycidylether of bisphenol-A and containing 4-aminoazobenzene covalently attached to the polymer chains have been studied. The material was shown to exhibit fast nonlinear response (relaxation time about 20 ns, χ⁽³⁾= 5 × 10^{- 8} esu) together with slow one (relaxation time of the order of tens of hours). This makes it possible to record fast and long life (quasi stationary) phase holograms. An analysis of possible mechanisms for the refractive index nonlinear behavior in the new structure is presented. In particular, a role of electronic, thermal, orientation, and isomerization processes is discussed. It was for the first time shown that the rotational and inversion mechanisms of the cis → trans isomerization of the azo-compounds have determinative effect upon kinetics of the nonlinear refractive index relaxation. For the rotational mechanism the relaxation time was found to be 10^-4 s meanwhile for the inversion mechanism it was 10⁵ s.

Formation of gratings by means of the photoinduced alignment change of polymer liquid crystals (PLCs) has been explored in a glassy state. To obtain high diffraction efficiency (η), we synthesized highly birefringent PLCs containing an azobenzene group directly connected with a tolane moiety (3ATm), in which the alkyl spacer length (CH₂)_m was varied as m=6, 9 and 12. It was found that the values of birefringence in all the PLCs were about 0.4. The behaviors of the photoinduced alignment change and the formation of gratings were found to be dependent on the alkyl spacer length of 3ATm.

Cholesteric liquid crystals (CLCs) which possess a periodicity in the visible portion of the spectra, exhibit selective reflection of circularly polarized light. The ability to modulate this color through a variety of means has been explored, including work which incorporated azobenzene LCs. Two types of systems have recently been explored utilizing wavelength-specific cis-trans isomerization processes, which enable unprecedented photosensitivity. The first system exhibits large blue or red-shifted changes in reflection wavelength upon visible irradiation. The second system exploits the metastable, long-lived photoinduced isotropic state, whose return to the reflective Grandjean texture can be induced by wavelength-specific radiation. We demonstrate nonlinear transmission from both types of systems, starting with submicrowatt power levels and spanning over four orders of magnitude dynamic range. The power dependence and temporal evolution of this effect (10–100 ms) is documented here for red or green laser wavelengths. The effect for the former case is due to bandgap auto-tuning, when the laser beam is tuning the CLC Bragg reflection band to its own wavelength. For the latter case, autonomous, optical feedback due to bandgap restoration is the cause of the nonlinear transmission properties.

The ability of optical axis gratings (OAGs) to fully transfer the energy of an unpolarized incident light beam into the ±1st diffraction orders is explored below for development of a polarization-independent optical system with nonlinear transmission. Diffractive properties of OAGs based on azo dye doped liquid crystals (azo LCs) are efficiently controlled with low power radiation. Switching from diffractive to transmissive states of the OAG takes place within 50 ms at 60 W/cm² power density level, while the diffractive state is restored within ~ 1 s in the absence of radiation. High contrast optical switching is demonstrated with violet as well as green laser beams. A photoswitchable OAG is paired with a light-insensitive OAG in diffraction compensation configuration to obtain an optical system switchable from high to low transmission state. The thinness of OAGs required for high contrast switching ensures high overall transmission of the system. Given also the spectrally and angularly broadband nature of OAG diffraction and the capability of azo LC material systems to respond both to cw as well as short laser pulses makes the optical system under discussion very promising for optical switching applications. Presentation of these results is preceded by an "opinionated" review of prior developments and demystifying of the fabrication technique of high efficiency large area OAGs.

We give an overview of our recent work on improving the optical performance of polymeric materials via supramolecular concepts, i.e., by making use of spontaneous non-covalent interactions between the chromophores and the polymer backbone. More precisely, we show that the aggregation of dipolar chromophores in amorphous polymeric materials can be controlled by simply choosing a proper polymer matrix. This approach has a potential impact in a wide range of optical phenomena where chromophore aggregation or phase separation sets a limit to the system performance.

In this work, we report preliminary results obtained for methacrylic polymers incorporating azobenzene side-group as nonlinear optical (NLO) active molecule. The trans-cis isomerization properties are discussed. The third-order non-resonant nonlinear refractive index (n₂) and nonlinear absorption coefficient (β) are measured using the Z-scan technique at 1064 nm in the picosecond regime. The influence of different electron-acceptor groups in azobenzene moieties on the nonlinear properties is investigated.

We have investigated the photoresponsive behavior of homogeneously aligned low-azobenzene-concentration crosslinked liquid-crystalline polymers. We compared the thermal contraction and photocontraction of the films, and show that upon UV irradiation, they bend efficiently towards the actinic light source. The photoinduced bending is studied both under continuous-wave irradiation and irradiation with nanosecond pulses. Pulsed irradiation revealed that the photomechanical response can take place within sub-millisecond time scale, and that even a single laser pulse can cause the sample to bend.

Aniline is oxidized to nitrosobenzene as the initial product, which undergoes further oxidation to nitrobenzene. The nitrosobenzene formation is catalyzed by functionalized multiwalled carbon nanotubes (CNT) followed by a coupling reaction between nitrosobenzene and aniline to produce azobenzene. This coupling requires close proximity of the reactants. It proceeds rapidly resulting in the UV-VIS absorption spectrum showing maxima at 327 nm and 425 nm. The nitrosobenzene yield in the presence of CNTs is controlled by the amount present in the medium. As the reaction is not catalyzed by unfunctionalized CNTs or graphitic particles, the uniqueness of the functionalized multiwalled CNTs in this catalysis suggests a nanodimensional reaction pathway.

Monolayers of thymine amphiphile containing azobenzene chromophore (Azo-Thy) were prepared on various aqueous oligonucleotide (dA₃₀, d(GA)₁₅, d(GGA)₁₀) subphases. Pressure–area isotherms and reflection absorption spectra of the monolayers on dA₃₀ or d(GA)₁₅ solution showed that the H-aggregate of the azobenzene units was formed at higher surface pressure than 25 mN/m. In contrast, the monolayer on an aqueous d(GGA)₁₀ solution did not form any aggregates of the azobenzene units even at high surface pressure. Base-pair formation between Azo-Thy and template d(GGA)₁₀ could give free volume to the azobenzene units in the monolayer to prevent the aggregation of the azobenzene units at the air–water interface.

In order to construct chromophores arrays that precisely controlled their arrangement, monolayers of an azobenzene bearing nucleoamphiphile were prepared on various oligoDNA solutions. Monolayers of the amphiphilic adenine derivative bearing an azobenzene moiety (C₁₂AzoC₅Ade) were prepared on thymidylic acid tetramer (dT4) and octamer (dT8) solutions, and UV-vis reflection absorption spectra of the monolayers were measured to investigate aggregation structures of the azobenzene. The absorption maximum of the monolayer was blue-shifted on the dT4 solution and red-shifted on the dT8 solution. It shows that azobenzene groups in the monolayer have parallel orientation (H aggregate) on the dT4 solution. Though, azobenzene groups have head-to-tail orientation (J aggregates) on the dT8 solution. When monolayers of C₁₂AzoC₅Ade were prepared on the synthesized cyclic oligonucleotides, the absorption spectra were totally different from those of the corresponding linear oligonucleotides.

A series of polymers bearing azobenzene and carbazole groups for photorefractive purpose were prepared via post-azo-coupling reaction. The successful reaction was identified by spectroscopic analysis and gel permeation chromatography. This approach is more facile compared with the direct polymerization of corresponding functional monomer. The polymers prepared have weight average molecular weight of higher than 1.5×10⁴ and are easily soluble in common organic solvents like chloroform and tetrahydrofuran, polymer films with high optical quality could be easily fabricated through solution casting. Glass transition temperature (T_g) of the polymers ranges from 60°C to 182°C, depending on the alkylene spacer length between the functional side group and the polymer backbone, and the polymers are relatively stable under 300°C.

Two novel polyacetylenes bearing nonlinear optical chromophoric group poly(3-(4-[4-(n-butyloxy)phenylazophenyl]carbonyl)oxy-1-propyne) (poly(1a)) and poly(3-(4-[4-(n-heptyloxy)phenylazophenyl]carbonyl)-oxy-1-propyne) (poly(1b)) were synthesized with [Rh(nbd)Cl]₂-Et₃N as catalysts. These polyacetylenes are soluble by using an alkyl spacer and an alkyloxyl group as a substituent. They were characterized by FTIR, NMR, GPC and UV-Vis and their optical limiting and nonlinear optical properties were investigated using 8 ns pulse at 532 nm wavenumber. The results show that these soluble functional polyacetylenes possess optical limiting properties and large nonlinear optical properties and poly(1b) possesses better optical limiting and nonlinear optical properties than poly(1a).

In this study, a synthetic procedure for unsymmetrical metallophthalocyanines of the form M[Pc(AB₃)], where A and B refer to two different types of peripheral functionality, has been developed and the new compounds have been converted to monomeric and dimeric palladium complexes. Asymmetrically substituted phthalocyanines were synthesized with the well-known statistical condensation method, by using two differently substituted precursors, namely 4-(2-ethoxyethoxy)-1-2-dicyanobenzene (1) and 4-{4-[Z/E]-phenylazo]-1-naphthyl}oxy-1,2-dicyanobenzene (2). Consequently, electron-donating 2-ethoxyethoxy groups and electron-withdrawing palladium complex are present in the same structure. Cyclopalladation was performed with [Pd(PhCN)₂Cl₂] to yield the bis-μ-chloro-bridged dimers and subsequently, the corresponding monomers were obtained by refluxing with three equivalents of potassium acetylacetonate. The resulting products were purified by column chromatography and characterized by several chemical and spectroscopic analysis methods. All compounds have very high solubility in organic solvents due to the presence of 2-ethoxyethoxy moiety.

An orthogonally arranged conjugate comprised of two rhodium(III) tetrakis-4-tolyporphyrins linked with an azobenzene moiety through a covalent Rh-C (aryl) bond has been facilely synthesized and characterized. Although photochemical isomerization of the azobenzene component was not observed, addition of trifluoroacetic acid (TFA) to the conjugate in a toluene solution causes significant colorimetric changes. UV-vis absorption, resonance light scattering (RLS), ${}^{\mathrm{\text{1}}}$H-NMR and IM-MS spectra were employed to investigate the pH-dependent chromogenic behavior of the triad, which gives a new pathway for construction of pH-dependent assemblies of porphyrin-azobenzene complexes.

Photosensitive microcapsules are important targets for medical, pharmaceutical, agriculture, consumer goods and chemical companies. In this study, we report the development of UV-sensitive capsules containing vanillin as a model encapsulated active material. Polyamide microcapsule shells containing azobenzene moieties in the main chain of the polymer were fabricated by oil-in-water interfacial polymerization method. Triggered perfume release and morphological variations of the microcapsule shell during UV light irradiation were observed by means of high-performance liquid chromatography (HPLC) and optical microscopy.

We have chosen two types of azobenzene derivatives to elucidate the correlation between molecular structure and fluorescence color of light-driven azobenzene-based aggregates. The fluorescence color from azobenzene molecules (1 and 2), adopting a planar structure, was obviously red-shifted from that of the corresponding twisted ortho-alkylated azobenzene 3. The steric hindrance resulting from bulky alkyl groups at the ortho position of the azo linkage was considered to lessen the intermolecular π – π stacking between aromatic rings, leading to the relatively smaller spectral shift in fluorescence from the absorption band of the initial azobenzene solution. The substitution of electron-withdrawing groups into the azobenzene core gave rise to a blue-shift in fluorescence wavelength. That is, the extended π-conjugated system consisting of a planar azobenzene core as well as the electronic properties of the substituents are key factors influencing the fluorescence color from the light-driven azobenzene aggregates. Moreover, we could prepare fluorescent polymer films by mixing fluorescent azobenzene aggregates with polymers. The fluorescence colors from the polymer films were comparable to those from the azobenzene aggregates.

The synthesis and reactivity of uranium complexes supported by a bis(aryloxide) cyclam ligand are surveyed. The hemilability of this ligand proved to be particularly appropriate to stabilize highly reactive uranium(III) and uranium(IV) complexes that were able to activate different unsaturated molecules. Of note are the reductive cleavage of azobenzene with the unprecedented formation of a trans-bis(imido) uranium(VI) complex and its reaction with carbon dioxide to generate a trans-oxido-imido uranium(VI) complex and phenyl isocyanate. The formation of a trans-dioxido uranium(VI) (uranyl) complex was also observed in the reaction of uranium(IV) complexes with sodium nitrite. Quantum chemical computations and solution ¹⁵N NMR spectroscopy were employed to evaluate bond covalency in the three {E=U=E}²⁺ complexes (E = O, NR).

Monolayers of thymine amphiphile containing azobenzene chromophore (Azo-Thy) were prepared on various aqueous oligonucleotide (dA₃₀, d(GA)₁₅, d(GGA)₁₀) subphases. Pressure–area isotherms and reflection absorption spectra of the monolayers on dA₃₀ or d(GA)₁₅ solution showed that the H-aggregate of the azobenzene units was formed at higher surface pressure than 25 mN/m. In contrast, the monolayer on an aqueous d(GGA)₁₀ solution did not form any aggregates of the azobenzene units even at high surface pressure. Base-pair formation between Azo-Thy and template d(GGA)₁₀ could give free volume to the azobenzene units in the monolayer to prevent the aggregation of the azobenzene units at the air–water interface.