Synthesis,Photophysical Properties of Tribranched Chromophores Based on 1,3,5‐Triazine Core and Different Electro‐donating End‐groups

Three two‐photon absorption (TPA) tribranched chromophores were successfully prepared, in which 1,3,5‐triazine is been as electron deficient core, 1,4‐phenylenedivinylene as conjugated bridge, 3,4‐ethylenedioxythiophene (EDOT) ( T1 ), N‐methylpyrrole ( T2 ) or triphenylamine ( T3 ) as electron‐donating end‐groups. Their photophysical properties were studied by absorption, one‐ and two‐photon fluorescence and TPA cross‐section determination. The nonlinear transmission (NLT) measurement in femtoseconds (fs) regime at 800 nm indicates that TPA cross‐section (₂ values of T1 , T2 and T3 with extended Π‐conjugated bridge are much larger than the corresponding chromophore T4 with a short length bridge, and TPA cross‐section of T1 with end‐groups EDOT exhibits a remarkable enhancement compared with T2 and T3 having the same length Π‐system. The chromophores T1 , T2 and T3 show also remarkable up‐converted luminescence and optical limiting activity.     

Theoretical investigation of one- and two-photon spectra of pyrazabole chromophores

Abstract  

An extensive series of pyrazabole chromophores containing pseudo-conjugated systems have been theoretically constructed and investigated on the one-photon absorption (OPA) and two-photon absorption (TPA) properties by using density functional theory and Zerner’s intermediate neglect of differential overlap methods. The results indicated that all the pyrazabole chromophores show strong OPA at around 400 nm and intense TPA properties in the range of 500–600 nm with TPA cross sections (δ _max) as large as 540–3,560 GM, which are excellent candidates for optical power limiting materials. It is noteworthy that the δ _max values of the two constructed pyrazaboles, PA3 and PAF2, are 308.8 GM at 772.0 nm and 157.8 GM at 834.4 nm, respectively, which may be particularly attractive as probes for two-photon fluorescence imaging. The influence of incorporating electron acceptors in the central core, π-conjugated bridge and terminal groups on OPA and TPA properties was analyzed in detail to derive structure–property relationships and to lay the guidelines for both spectral tuning and amplification of molecular TPA in the target region. Meanwhile, the solvent effects on these properties were taken into account within the PCM model. The solvent has a significant impact on the TPA properties for chromophore PA3 and leads to the two-photon absorption spectra (λ _max ^T ) red-shift and δ _max enhancing relative to those in gas phase. In addition, from the calculations of molecule AlA2, we can draw the conclusion that the compounds with the Al₂N₄ center behave similarly to pyrazabole chromophores in the linear optical and TPA properties and increase TPA cross sections to some extent.     

Fluorene as the π-spacer for new two-photon absorption chromophores

We report herein the design and synthesis of two new quadrupolar D-π-A-π-D chromophores containing diphenyl amine and dicyanobenzene or 2,1,3-benzothiadiazole as electron donor (D) and acceptor (A), respectively, which are bridged by fluorene linkage (π). The introduction of coplanar fluorenes is highly beneficial for the enhancement of two-photon absorption (TPA), where 1b displays a TPA cross section (σ₂) of up to 1975±207 GM.     

多枝[1,3,4]-噁二唑衍生物的双光子吸收和光功率限幅特性

采用非线性透过率法测定了多枝[1,3,4]-噁二唑衍生物的双光子吸收性质. 测定了化合物的单光子荧光光谱和双光子荧光光谱, 在800 nm波长的激光激发下, 9-乙基-3,6-双{5-(4-叔丁基苯基)-[1,3,4] 噁二唑-2-苯乙烯基}-咔唑(3)和三-{5-(4-叔丁基苯基)-[1,3,4] 噁二唑-2-苯乙烯基-4-苯基}-胺(4)能够发出很强的蓝色和黄绿色双光子上转换荧光, 荧光峰分别位于485和547 nm. 这些多枝结构化合物的双光子吸收截面较大(数值超过104 GM), 并具有很强的光限幅效应. 多枝分子中重复单元的推拉电子结构和协同效应有效地增强了分子的双光子吸收性质.     

Synthesis and properties of tribranched chromophores with triazine and fluorene units

Two tribranched chromophores,1,3,5-triazine as electron deficient core,9,9-dimethylfluorene asπ-conjugated bridge, diphenylamino(4a) and naphthylamino(4b) as electron-donating end-groups,were successfully prepared via Buchwald-Hartwig coupling reaction.Their linear photophysical and two-photon absorption(TPA) properties were investigated by absorption, fluorescence and nonlinear transmission method,respectively.The absorption cut-offs of the chromophores are below 550 nm and both chromophores have strong fluorescence emission.The compound 4a(206.3 GM) exhibits larger TPA cross-section than 4b (57.8 GM) in the femtosecond regime at 800 nm.     

Two-photon absorption chromophores with a tunable [2,2′]bithiophene core

Sonogashira coupling between 3,5,3′,5′-tetrabromo-[2,2′]bithiophene and various terminal alkynes provides two-photon absorption (TPA) chromophores 1-6, which possess electron donor (D) and/or acceptor (A) alkynyl substituents at 3(3′) and 5(5′) sites of the bithiophene core. The up-converted fluorescence emission excited at 800 nm (Ti:sapphire femtosecond laser, ∼100 fs pulses) was used to determine the two-photon absorption cross-sections (σ) of these compounds. The corresponding TPA cross-section (σ) values ranging from 132 to 1120 GM (10⁻⁵⁰ cm⁴ s photon⁻¹) can be fine-tuned by the substitutents. The quadrupolar-type (A-π-D-π-A) chromophore 5 exhibits the largest σ value (1120 GM) in CH₂Cl₂ upon 800 nm excitation.     

Benzothiazoles with tunable electron-withdrawing strength and reverse polarity: a route to triphenylamine-based chromophores with enhanced two-photon absorption

A series of dipolar and octupolar triphenylamine-derived dyes containing a benzothiazole positioned in the matched or mismatched fashion have been designed and synthesized via palladium-catalyzed Sonogashira cross-coupling reactions. Linear and nonlinear optical properties of the designed molecules were tuned by an additional electron-withdrawing group (EWG) and by changing the relative positions of the donor and acceptor substituents on the heterocyclic ring. This allowed us to examine the effect of positional isomerism and extend the structure-property relationships useful in the engineering of novel heteroaromatic-based systems with enhanced two-photon absorption (TPA). The TPA cross-sections (δ(TPA)) in the target compounds dramatically increased with the branching of the triphenylamine core and with the strength of the auxiliary acceptor. In addition, a change from the commonly used polarity in push-pull benzothiazoles to a reverse one has been revealed as a particularly useful strategy (regioisomeric control) for enhancing TPA cross-sections and shifting the absorption and emission maxima to longer wavelengths. The maximum TPA cross-sections of the star-shaped three-branched triphenylamines are ～500-2300 GM in the near-infrared region (740-810 nm); thereby the molecular weight normalized δ(TPA)/MW values of the best performing dyes within the series (2.0-2.4 GM·g(-1)·mol) are comparable to those of the most efficient TPA chromophores reported to date. The large TPA cross-sections combined with high emission quantum yields and large Stokes shifts make these compounds excellent candidates for various TPA applications, including two-photon fluorescence microscopy.     

Diaza-18-crown-6 based chromophores for modulation of two-photon absorption cross-section by metal ions

Two chromophores with diaza-18-crown-6 as receptor have been synthesized in high yields. The electronic structure, one-photon absorption (OPA) spectra, and two-photon absorption (TPA) properties have been studied in detail. When no metal ion is added as input, both show negligible TPA cross-section (σ₂). However, in the presence of Zn(II)/Cd(II)/Mg(II)/Ca(II) ion, each exhibits large TPA cross-section value. Binding of metal ion in the receptor increases the symmetric charge transfer leading to large σ₂ values. Theoretical calculations at the B3LYP functional with 6-31G^∗ and LanL2DZ mixed basis set under DFT formalism support experimental results.     

Synthesis and bioactivity of N-cyclopropanecarboxyl-N′-pyridin-2-yl thiourea derivatives and related fused ring compounds

Cyclopropanecarboxylic acid or 2,2-dimethyl cyclopropanecarboxylic acid was used as a leading compound for its biological activity.Six new N-(substituted) cyclopropanecarboxyl-N′-pyridin-2-yl thioureas were prepared.Compound 5 was obtained by oxidizing cyclization of compound 4 in the presence of bromine in chloroform solution.The structures of 4 and 5 were confirmed by ~1H NMR and elemental analysis.The preliminary biological tests indicate that compound 4b and 4e have excellent herbicidal activity,and ...     

Synthesis and Optical Properties of HyperbranchedPAEKs Containing Porphyrin and Its Metal Derivatives简

Novel functional hyperbranched poly(aryl ether ketone)s(HPAEKs) bonded with nonlinear optical chromophores(meso-tetrakis(4-hydroxyphenyl) porphyrin, THPP and its metal derivatives) were synthesized and characterized by 1H-NMR and UV-Vis absorption spectra. The incorporation of chromophores into HPAEKs endowed HPAEKs novel NLO and OL properties. Indeed, dendritic architecture allowed for maximum dispersion of the chromophores, avoided aggregation, more optical limiting property was obtained. Simultaneously, they retained the excellent properties of the materials, particularly in thermal stability. Their optical properties were evaluated by nonlinear optical analyses and optical limiting. The results showed that these polymers possessed good optical limiting(OL) property and large nonlinear optical(NLO) susceptibilities(ca. 10 12esu). All polymers containing chromophores presented excellent thermal stability(DT5 524.17 °C).     

Push-pull alkenes from cyclic ketene-N,N′-acetals: a wide span of double bond lengths and twist angles

Push-pull alkenes can be quickly accessed by cyclic ketene-N,N′-acetal chemistry. A number of push-pull structures with a wide span of double bond lengths and twist angles were synthesized from the reactions of (1) N,N′-dimethyl cyclic ketene-N,N′-acetals with isocyanates, (2) the products from (1) with isocyanates, (3) 2-methylimidazoline and 2-methyl-1,4,5,6-tetrahydropyrimidine with diacid chlorides, (4) 2-methylimidazoline, and 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine with benzoyl chlorides, and (5) 1,2-dimethylimidazoline and 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine with aryl isocyanates. These reactions proceed under very mild conditions and give moderate to excellent yields. X-ray crystallographic analysis of eight pxush-pull alkenes indicates that the central double bond lengths and twists are sensitive to the ring sizes (5 or 6), ring structures (fused or non-fused), electron donating and withdrawing strengths of pushing and pulling portions, respectively, number of electron pushing or pulling groups and substituent steric effects.     

Polycyclic aromatic hydrocarbon-substituted push–pull chromophores: an investigation of optoelectronic and nonlinear optical properties using experimental and theoretical approaches

A series of new push–pull chromophores were synthesized in moderate to very high yields (65%–97%) by treating TCNE and TCNQ with alkynes substituted by electron-rich diethylaniline and polycyclic aromatic hydrocarbons. Some of the chromophores exhibit strong intramolecular charge-transfer bands in the near-IR region with λ_max values between 695 and 749 nm. With the help of experimental and theoretical analysis, it is concluded that the trend in λ _max values is affected by PAH substituents sterically, not electronically. Steric constraints led to the increased dihedral angles, reducing conjugation efficiencies. The absorption properties of push-pull compounds have been investigated in solvents possessing different polarities. All chromophores exhibited positive solvatochromism. As an additional proof of efficient charge-transfer in push–pull chromophores, quinoid character (dr) values were predicted using calculated bond lengths. Remarkably, substantial dr values (0.045–0.049) were predicted for donor diethylaniline rings in all compounds. The effects of various polycyclic aromatic hydrocarbons on optical and nonlinear optical properties were also studied by computational methods. Several parameters, such as band gaps, Mulliken electronegativity, chemical hardness and softness, dipole moments, average polarizability, first hyperpolarizability, were predicted for chromophores at the B3LYP/6-31++G(d,p) level of theory. The predicted first hyperpolarizability β_(tot) values vary between 198 to 538 × 10^–30 esu for the reported push–pull chromophores in this study. The highest predicted β_(tot) value in this study is 537.842 × 10^–30 esu, 8150 times larger than the predicted β_(tot) value of benchmark NLO material urea, suggests possible utilization of these chromophores in NLO devices. The charge-transfer character of the synthesized structures was further confirmed by HOMO-LUMO depictions and electrostatic potential maps.     

Novel heterocycle-based two-photon absorbing dyes

[structure: see text]. The synthesis and nonlinear optical characterization of two novel heteroaromatic-based chromophores is described. The new dyes present an A-pi-D-pi-A general framework, where A is a pi-deficient heteroaromatic ring (pyridine, quinoline, benzothiazole) and D a pi-excessive pyrrolyl moiety. Both systems exhibit large two-photon absorption (TPA) values in the femtoseconds regime (TPA cross section as high as 150 x 10(-50) cm(4) s photon(-1) molecule(-1) with 150 fs laser pulses). Their TPA-based optical limiting activity is also shown.     

Enhancement of two-photon absorption cross-section in macrocyclic thiophenes with cavities in the nanometer regime

The linear and nonlinear optical properties of two thiophene-based cyclic molecules have been investigated. These molecules represent nanometer sized cavities which may be useful for novel photonic devices. By virtue of long-range interactions, these chromophores serve as novel architectures for enhanced two-photon absorption (TPA) properties. Measurements of the different size ring structures showed a 550% increase in the TPA cross-section for the larger macrocycle. Electronic structure calculations have suggested an increase in coupling of the excited states in these systems as the ring size is increased. Measurements of the ultrafast transient absorption and fluorescence were carried out with these systems in order to probe the interaction between the chromophores. The results of the transient decays as well as fluorescence anisotropy decay times gives stronger proof to the suggestion of delocalized states in the cyclic macrocycles. These results provide information regarding the optical properties of these novel systems useful for potential applications in photonics.     

Synthesis and hyperpolarizabilities of high temperature triarylamine-polyene chromophores

The synthesis and hyperpolarizabilities of a series of push-pull chromophores containing bis-(4-methoxyphenyl)-amine donor and efficient acceptors bridged with ring locked polyene are presented. The chromophores are readily soluble in common organic solvents and exhibit high thermal decomposition temperatures (highest T_d = 330 °C). Molecular hyperpolarizabilities (β) of the chromophores were measured by Hyper Rayleigh Scattering (HRS) at 1604 nm (highest β = 20,000 × 10⁻³⁰ esu). These chromophores can be used to develop electro-optic (EO) materials due to their large optical nonlinearities, good absorption characteristics, high thermal decomposition temperatures, and excellent solubility with organic solvents and polymeric materials.     

Theoretical prediction of one- and two-photon absorption properties of N-annulated quaterrylenes as near-infrared chromophores

Graphene nanoribbons (GNRs) have attracted increasing attention due to high potentiality in nanoelectronics. In the present study, quantum-chemical calculations of structural and nonlinear optical properties have been first carried out for the nanoelectronical materials, a new series of ladder-type N-annulated quaterrylenes and their imide chromophores. The effects of the solvent, terminal groups, the number of N-annulated bridges, and π-conjugated length are discussed in detail. The solvent effect is significant on the one-photon absorption (OPA). Moreover, the OPA and two-photon absorption (TPA) properties of the two series of DI and N-MI molecules show a clear solvent dependence, which is attributed to the carboximide substitution featuring larger polarization. Introducing electron-donating groups and dicarboximides and increasing the conjugated length lead to red-shifts of the OPA, emission, and TPA spectra, lower emission lifetimes, and enhanced TPA cross sections (δ(max)), but further extension of the conjugated framework does not always promote an increase of δ(max). The changing trends of δ(max) can be explained by the transition moment and the intramolecular charge transfer. All N-annulated quaterrylene and their imide derivatives possess small energy gaps, intense near-infrared absorption and emission, and large δ(max), which are important for use as two-photon fluorescent labeling materials.     

Degenerate two-photon-absorption spectral studies of highly two-photon active organic chromophores

Degenerate two-photon absorption (TPA) spectral properties of five AFX chromophore solutions have been studied using a single and spectrally dispersed sub-picosecond white-light continuum beam. In a specially designed optical configuration, optical pathways inside the sample solution for different spectral components of the focused continuum beam were spatially separated from each other. Thus, the nondegenerate TPA processes coming from different spectral components can be eliminated, and the direct nonlinear absorption spectrum attributed to degenerate TPA processes can be readily obtained. Using this new technique, the complete TPA spectra for these five highly two-photon-active compounds (AF-380, AF-350, AF-295, AF-270, and AF-50) were obtained in the spectral range from 600 to 950 nm on an absolute scale of TPA cross section. The relationship between the molecular structures and their TPA spectral behaviors are discussed. In general the measured TPA spectra are not identical with the linear absorption spectra on the scale of absorbed photon(s) energy. Moreover, for some sample (such as AF-380), the TPA spectrum is totally different from the linear spectrum, which implies the difference of molecular transition pathways and selection rules for one- and two-photon excitation processes. At high excitation intensity levels (>or=15 GW/cm(2)), the saturation behavior of TPA transition can be observed obviously in AF-350 and AF-380 solutions that exhibit much higher nonlinear absorptivity than the other chromophores investigated.     

Metal-acetylide addition to tetracyanoethylene

Two push-pull chromophores that have shown utility in the field of molecular electronics and non-linear optics are DDMEBT (1, 2-(4-dimethylamino)phenyl)-3-((4-(dimethylamino)phenyl)ethynyl)buta-1,3-diene-1,1,4,4-tetracarbonitrile) and TDMEE (2, 4-(4-dimethylamino)phenyl)but-1-en-3-yne-1,1,2-tricarbonitrile). Unfortunately, the methods reported for their synthesis give variable yields, use toxic solvents, and only provide small amounts of material. We report improved synthetic protocols, providing access to larger quantities of material. By investigating multiple metal-acetylides of 4-ethynyl-N,N-dimethylaniline and their subsequent addition to TCNE, we obtained various products depending on the identity of the metal ion. This led to the simple synthesis of push-pull chromophoric compounds.     

Synthesis and structure-linear and structure-nonlinear optical properties of multi-dipolar zigzag oligoaryleneethynylenes

A novel series of monodisperse, multi-dipolar zigzag oligoaryleneethynylenes DA(n) and D-Ar-A(n), bearing electron-donating dibenzothiophene and electron-accepting dibenzothiophene dioxide as arenes, with up to six charge-transfer (dipolar) units have been designed and synthesized by palladium-catalyzed Sonogashira coupling reactions. The linear and nonlinear optical properties of these multi-dipolar oligoaryleneethynylenes can easily be modified or enhanced by incorporating/extending with various central aryleneethynyl moieties such as phenylethynyl, oligo(9,9-dibutylfluorenyl)ethynyl, and oligothienylethynyl within the donor-acceptor units. Interestingly, the absorption and emission of these zigzag oligoaryleneethynylenes are not dependent on the number of covalently linked dipolar chromophores; however, the fluorescence quantum efficiencies consistently decrease with increased number of covalently linked dipolar units. These zigzag oligoaryleneethynylenes exhibit a linear increase in the two-photon absorption (TPA) cross-sections with increased number of covalently linked dipolar units without red-shifting the absorption and emission spectra. In addition, very large TPA cross-sections in the femtosecond regime (sigma(800) = 1306 GM in DMF or sigma(750) = 1522 GM in CH(2)Cl(2)) were obtained for D-TF-A(4) despite the moderate strength of the donor-acceptor pair. Our results suggest that the TPA properties of these zigzag oligoaryleneethynylenes including TPA wavelength and TPA cross-section can easily be tuned by means of modifying the central aryleneethynylene units and increasing the number of dipolar units, respectively. This approach provides an alternative means to tune or enhance the TPA cross-section at a specific wavelength.     

Very large infrared two-photon absorption cross section of asymmetric zinc porphyrin aggregates: Role of intermolecular interaction and donor-acceptor strengths

Very large two-photon absorption (TPA) cross sections at the infrared region have been revealed for J-aggregates of asymmetric zinc porphyrin using quantum-chemical calculation. The TPA properties are evaluated for monomer and aggregates of a series of push-pull porphyrins, whose syntheses are known in the literature. The two-photon absorption cross section can be greatly enhanced by increasing the strengths of the electron donor/acceptor. We also present a quantum-chemical analysis on porphyrin aggregates to understand the role of intermolecular interactions and the relationship between structural and collective nonlinear optical properties. It has been observed that the TPA properties change tremendously as monomers undergo J-aggregation and the magnitudes of TPA cross sections are highly dependent on the nature of aggregates. The importance of our results with respect to the design of photonic and photodynamic therapy materials has been discussed.