In recent years, there has been extensive research and continuous development on second-order nonlinear optical (NLO) crystal materials due to their potential applications in telecommunications, THz imaging and spectroscopy, optical information processing, and optical data storage. Recent progress in second-order NLO ionic organic crystal materials is reviewed in this article. Research has shown that the second-order nonlinear optical properties of organic crystal materials are closely related to their molecular structures. The basic structures of ionic organic conjugated molecules with excellent nonlinear optical properties are summarized. The effects of molecular structure, for example, conjugated π electron systems, electronic properties of donor-acceptor groups, and different counter-anion effects on second order NLO properties and crystal packing are studied.

Molecular Structures and Second-Order Nonlinear Optical Properties of Ionic Organic Crystal Materials

The construction of metal-organic frameworks (MOFs) with hierarchical pores is of great importance for the photocatalytic oxidation (PCO) of gaseous BTXS (benzene, toluene, xylenes and styrene) pollutants with large molecular size, but it is still challenging. Herein, by adjusting the ratio of anions (NO3- and Cl-) in the metal precursors, hierarchically porous MIL-100(Fe) MOF/MOX homojunctions were obtained through a one-pot solvothermal method. The existence of both micro- and mesopores (2–10 nm) made the active sites more accessible to guest molecules. The formation of MOF/MOX homojunctions promoted the separation of electron-hole pairs. Additionally, the coordinatively unsaturated acidic Fe3-O sites facilitated the capture of BTXS molecules and participated in the PCO process through the conversion between Fe(III) and Fe(II). The MIL-100(Fe) homojunctions showed improved performance towards the PCO of BTXS (over 80% for xylenes and styrene) compared with the crystalline or xerogel counterparts and exhibited great potential in the PCO of aromatic air pollutants. 

One-pot Synthesis of the MIL-100 (Fe) MOF/MOX Homojunctions with Tunable Hierarchical Pores for the Photocatalytic Removal of BTXS

Three polyoxometalates (POMs) functionalized by tetrathiafulvalene (TTF) molecules have been synthesized by a coupling reaction between the Anderson-type POMs [MnMoO{(OCH)CNH}] or [AlMoO(OH){(OCH)CNH}] and the TTF carboxylic acid derivative (MeS)TTF(S-CH-COH). The monofunctionalized TTF-AlMo POM contains one TTF group covalently grafted on an Al Anderson platform. The symmetrical TTF-MnMo-TTF POM possesses two TTF groups grafted on each side of a Mn Anderson derivative while the asymmetrical TTF-MnMo-SP POM contains a TTF and a spiropyran groups. These three trianionic species have been characterized by elemental analysis, H and C NMR, FT-IR spectroscopy, ESI-MS spectrometry, and single-crystal X-ray diffraction (for TTF-MnMo-TTF). In the solid state, the grafted TTF molecules of TTF-MnMo-TTF POMs interact via S···S and π···π interactions and form chains. The electrochemical properties of the complexes reflect the contributions of both the inorganic POM and the TTF moieties. Despite adsorption of the oxidized hybrid species on the Pt grid working electrode, UV-vis-NIR spectroelectrochemical investigations evidence peaks characteristic of the oxidation of the TTF units. Finally, hyper-Rayleigh scattering (HRS) measurements show that the three novel TTF derivatives exhibit β values between 20 and 37 × 10 esu. Moreover it is observed that the oxidation of the TTF moieties by Fe ions increases the NLO response. These values are in the order of magnitude of that found for the well-known 4-dimethylamino- N-methyl-4-stilbazolium (DAS) cation (β = 60 × 10 esu).

/pdf/anderson-type-polyoxometalates-functionalized-by-4ytfzqylgw.pdf

Anderson-Type Polyoxometalates Functionalized by Tetrathiafulvalene Groups: Synthesis, Electrochemical Studies, and NLO Properties.

A new chalcone derivative 3-(1-methyl-1H-pyrrol-2-yl)-1-naphthalen-2-yl propenone (MPNP) with electron donor-acceptor group has been synthesized and characterized by IR, 1HNMR, 13C NMR and X- ray crystallography. Electronic absorption and emission spectra of MPNP have been studied in solvents of different polarity. A remarkable red shift was observed in the emission spectrum of MPNP compared to the absorption spectrum upon increasing the solvent polarity, indicating a higher dipole moment in the excited state than in the ground state and the transition involved are π-π* with charge transfer character. Lippert-Mataga and Reichardts correlations were used to estimate the change in dipole moments (Δμ); suggest that the emissive state of MPNP is of strong ICT character. Fluorescence quantum yield (ϕf) of MPNP was correlated with empirical solvent polarity parameter ET(30), and it is observed that ϕf increases with increase in solvent polarity of polar aprotic solvents and decrease in alcoholic solvents. The interaction of MPNP with colloidal silver nanoparticles (AgNPs) was also studied in ethanol and ethylene glycol using steady state emission measurements. The fluorescence quenching data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching of MPNP by Ag NPs.

Spectroscopic Investigation, Effect of Solvent Polarity and Fluorescence Quenching of a New D-π-A Type Chalcone Derivative

http://www.physics.ua.ac.be/~jcampo/Jeong_DyesAndPigments2015.pdf

N-Methylquinolinium derivatives for photonic applications: Enhancement of electron-withdrawing character beyond that of the widely-used N-methylpyridinium

the new salts trans-4-p-(dimethylamino)-N-R-4-pyridinium chloride (R = methyl (R1), 4-methoxyphenyl (R2), 3-methylphenyl (R3), phenyl (R4), 2,4-dinitrophenyl (R5)), with same conjugated systerm but different substitute, have been synthesied based on push -core-pull -core-push/pull structure. Fluorescence-free first hyperpolarizability β values of compounds R1 to R5 were measured by using hyper-Rayleigh scattering (HRS) technique in methanol solutions with an Nd:YAG nanosecond laser. Here fluorescence spectrometer (Edinburgh Instruments ltd, model FLS920) was used to eliminate background of two-photon fluorescence. The embedding phenyl into N-alkyl stilbazolium salts makes the planarity broken. So the two-photon fluorescence of compounds R2 to R5 decreases intensively compares with compound than The HRS results indicate that the N-aryl chromophores in compounds R3 to R5 has considerably larger β values than their N-methyl counterpart in compound R1. On one hand, the broken of planarity reduces their two-photon fluorescence and perhaps increases their β 0 . On the other hand, compound R5 with increasing electronegativity substitutes makes its β 0 increases due to the greater electron-withdrawing abilities of N-aryl- with respect to N-methyl pyridinium groups. An analogous molecular engineering strategy should also enhance the quadratic NLO activities of purely organic pyridinium dyes such as stilbazolium salts.

Quadratic Nonlinear Optical Properties of N-Aryl Stilbazolium Dyes

In this paper, we performed experimental and quantum-chemical studies on a series of symmetrically substituted phenylenevinylene chromophores with different lengths of conjugated chains and different electro negativity of substitution groups to provide an insight into the nature of the two-photon absorption (TPA) processes and to reveal structure-property relations. TPA spectra were obtained at the wavelengths ranging from 600 to 1000 nm with 6ns laser pulses of 10Hz repetition rate. The TPA spectra show that absorption band is mainly related to the transition of electrons btween the orbital localized at phenyl rings of the conjugated chains. Quantum-chemical calculations were performed with MOLCAO (Molecular Orbital as a Linear Combination of Atomic Orbitals) method to calculate the positions of the electronic levels and the shapes of the molecular orbitals. Considering all of the series of symmetrically substituted phenylenevinylene chromophores, the planar structure and the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is influenced significantly by the length of conjugated chains and the electro negativity of substitution groups. Structure-property relations revealed that the TPA cross section tends to be enhanced by an increase in the electro negativity of the substitution groups and tends to be reduced by an interruption of the conjugated chain.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Relations of two-photon absorption property and molecular structure in phenylenevinylene chromophores

A novel organic chromophore (A1) is designed and synthesized with a fine structure for two-photon absorption (TPA). The single-photon induced fluorescence spectra and the fluorescence lifetime have been studied for A1, excited respectively by 297-, 355-, 422-nm laser. And the two-photon induced fluorescence spectra were surveyed when A1 was excited by 820- and 910-nm laser. The results show that the curves of up-converted fluorescence spectra are almost same and have the same peak value at 518 nm. Accordingly, we can draw a conclusion that the TPA occurs when A1 is excited by 820- and 910-nm laser separately and though the absorption-transition pathway is different, the transition-emission pathway is the same.

Synthesis and two-photon induced fluorescence spectroscopy of a novel nonlinear optical chromophore

When a triphenylamine (TPA) is incorporated to a fluorephore of 2-Ethyl-6-(1-piperidinyl)-1H-benz[de]isoquinoline-1,3(2H)-dione (EPQD), energy absorbed by EPQD unit will mostly transfer to TPA unit inside the new molecule 2-(4-Diphenylamino-phenyl)-6-(1-piperidinyl)-1H-benz[de] isoquinoline-1,3(2H)-dione (APQD) through electron transfer, and then relax with no fluorescence APQD, whose fluorescence quenched by the intramolecular energy transfer, has a little larger two-photon absorption cross-section than its reference dye EPQD

Intramolecular energy transfer in a two-photon absorbing naphtahlimide-triphenylamine dyad

Multiphoton-absorption properties of π -conjugated symmetrical A - π - D - π - A chromophore, 3,6-Bis[2-{4-[5-(4-tert-butyl-phenyl)-[1,3,4]oxadiazol-2-yl]-phenyl}-vinyl]-N-ethylcarbazolyl, has been experimentally studied by using femtosecond laser pulse. At the wavelengths from 1205nm to 1570nm, the molecule shows large three-photon absorption (3PA) properties. The 3PA cross section reaches 4.5 * 10-24cm6Â·GW-2 at 1255nm. The output/input characteristic curve measured by nonlinear transmission method demonstrated a good optical power limiting performance based on 3PA mechanism. Luminous blue-green (about 477nm) up-conversion fluorescence excited by infrared laser pulse from 1205nm to 1570nm was easily observed in the quartz cuvette along the laser propagation direction. The material was also theoretically studied using Gaussian 03' software. The geometry, electronic structure, ground state charge distribution and excited state charge distribution were systematically calculated by HF/6-31G(d) and CIS/6-31G(d) method. Calculation results show that the obvious three-photon absorption and frequency up conversion fluorescence of this chromophore is attributed to its rigidity of chemical structure and effective charge transfer from the excited terminal units to the π -conjugated bridging units. The 1,3,4-oxadiazole is considered to be a good electron-acceptor and the key part in this charge transfer route. Particularly, for the first time we give the analytical solution to nonlinear transmission in a 3PA process when the incident beam has a Gaussian spatial profile.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Green frequency upconversion fluorescence of symmetrical 1,3,4-oxadiazole derivative by femtosecond three-photon excitation

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