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A series of optical polymeres were prepared by a Mitsunobu reaction from the correspondingN,N-dihydroxyethyl D-π-A chromophores and bisphenol A, which is new main-chain copolymeres with good solubility in ordinary organic solvents. The linear and nonlinear optical (NLO) properties were investigated by UV spectra and NLO measurements. The results indicate that the films of copolymeres exhibit a higher macroscopic second nonlinear optical coefficient, thermal stability and good optical transparency.

A novel octupolar chromophore with 1,3,5-triazine as core, 2,7-divinylene-9,9-dimethylfluorene as extended π-conjugated bridge, triarylamine as the electron-donating end-groups was successfully synthesized and characterized. Their linear photophysical and two-photon absorption (TPA) properties were investigated by UV absorption, excited fluorescence (SPEF) spectra and nonlinear transmission method, respectively. The absorption cut-off of the chromophore is below 520 nm and it has stronger fluorescence emission in a nonpolar solvent. In addition, the chromophore exhibits larger TPA cross-section (226.0 GM) in the femtosecond regime at 800 nm.

A series of H-shaped chromophores with two parallel and non-conjugated D-π-A units have been synthesized, in which a 9,10-dihydroanthracene was employed as molecular backbone. The synthesis of these H-shaped chromophores 9a–11a was accomplished via an eight-step reaction, including double Claisen rearrangement, hydroboration–oxidation, Rieche formylation reaction, Knoevenagel condensation and Corey–Fuchs reaction, with a total yield about 12.5%. The corresponding mono-D-π-A unit compounds 9b–11b were also prepared in a similar procedure for the purpose of comparison. Crystal structures of three intermediates 5a, 7a and 8a were measured, which demonstrate that the two D-π-A units in a single H-shaped chromophore molecule are nearly arranged at the same direction. The studies of UV–vis spectra and the solvatochromic method indicate that the molecular second-order polarizabilities values (μβ) of H-shaped chromophores are remarkably increased compared with the corresponding mono-D-π-A unit reference compounds, without causing a large shift of the absorption band to longer wavelength.

A series of new fluoro-containing copolymers have been synthesized by a Mitsunobu reaction with 4,4′-(hexafluoro- isopropylidene)bisphenol A (6FBPA) and the corresponding N, N-dihydroxyethylaminoaryl azo or ring-locked triene compounds, which have high thermal stability and good solubility in organic solvents. The nonlinear optical (NLO) measurements made by Marker fringe method at 1064 nm indicate that the copolymers embedded with the ring-locked triene and azo chromophores exhibit higher macroscopic nonlinear optical coefficient (70.2 pm/V and 26.5–34.6 pm/V, respectively). Thermal analysis and UV–visible absorption spectra show that the copolymers have good thermal stability (Td = 264–319 °C) and optical transparency (λmax

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.

A novel calix[4]arene chromophore 1 was synthesized by introduction of two D-π-A units (4-nitrophenyl)azophenyloxy groups) on the lower rim of calix[4]arene. The measurement results of hyper-Rayleigh scattering (HRS) and UV-vis spectra show that the static first molecular hyperpolarizability of the chromophore 1 is more than two times that of the corresponding mono-D-π-A unit reference compound 4-(4-nitrophenylazo)phenol 2, without causing red-shift of absorption band.

The octupolar chromophore TA with a 1,3,5-triazine core and pyrrole electron-donating end-groups was prepared via Knoevenagel coupling. Its photophysical and two-photon absorption (TPA) properties upon the protonation with CF 3 COOH were investigated by absorption, fluorescence, NMR spectroscopy and TPA cross-section determination. The UV–vis spectroscopic study shows that the absorption band is shifted from 401 nm to 471 nm with the color change from pale-yellow to red upon CF 3 COOH addition. The fluorescence spectra shows that the emission band is red-shifted from 490 nm to 553 nm accompanied by the distinct emission quench effect caused by the protonation. NMR spectropic study demonstrates the protonation of triazine upon CF 3 COOH addition, and the protonated molecule retain the C 3h symmetry. In addition, the theoretical calculations of the absorption spectra of neutral and protonated TA demonstrate an obvious red-shift of λ max in the absorption after protonation. TPA cross-section of TA measured by nonlinear transmission (NLT) exhibits the obvious TPA cross-section enhancement effect upon protonation, provides a simple way to enhance the TPA cross-section of molecules and makes it attractive for application involving the proton-controlled optical sensor.

The macroscopic second harmonic generation (SHG) coefficient (d33) of polymer depends on several factors, including the first hyperpolarizability (β) and dipole moment (μ) of chromophore, the combination of different donors (D) and acceptors (A), chromophore–chromophore electrostatic interactions, asymmetric structure of chromophore, the effect of main-chain on NLO properties of polymer, hydrogen bond and so on, therefore, several parameters should be comprehensively considered to design desired materials with high d33 value. Based on quantum chemical calculations, a polyimide containing isophorone derivatives as chromophores were designed and synthesized. Experimental results show that the polyimide exhibits a large macroscopic nonlinear optical coefficient (d33 = 63.9 pm V−1), thermal stability (Tg = 171 °C; Td = 308 °C) and good optical transparency (λmax = 418 nm). This paper could suggest a potentially practical way for designing effective NLO polymers.

Chromophores containing two parallel nonconjugated D-pi-A units are effective chromophores with high hyperpolarizability and good optical transparency. It provides a method for the design and synthesis of effective chromophores. The semiempirical method ZINDO was employed to study the relationship between enhancement of the static first hyperpolarizabilities (beta0) per D-pi-A unit and the number of parallel nonconjugated D-pi-A units in a chromophore. The results show that the chromophores containing two parallel nonconjugated D-pi-A units would exhibit higher beta0 values than two times the beta0 value of the corresponding reference chromophore containing a D-pi-A unit. The chromophore containing three parallel nonconjugated D-pi-A units exhibits the highest enhancement of beta0 per D-pi-A unit, which is 10.1 times the beta0 value of the corresponding reference chromophore. However, the beta0 value of the chromophore containing four parallel nonconjugated D-pi-A units is very small, and the enhancement of beta0 value per D-pi-A unit decreases sharply, from 10.1 to 0.3, with increasing the number of parallel D-pi-A units in a chromophore from 3 to 4. It could give a useful suggestion for designing chromophores containing parallel nonconjugated D-pi-A units.

Two new azo-dye chromophores containing different electron-acceptor groups were synthesized and characterized by 1 H NMR, FT-IR and UV-vis spectra, respectively. The second-order nonlinearity of azo-dyes doped films in poly (methylmethacrylate) and the first hyperpolarizability of the azo molecules were investigated by the Maker Fringe method and the solvatochromic method, respectively. Experimental results showed that both of the two dyes exhibited large second-order nonlinearity (d33 > 30 pm/v) and the stronger electron-acceptor groups in dye molecules would induce larger second-order nonlinearity. This was confirmed by the measurement of the first hyperpolarizability.

A series of H-shaped second-order nonlinear optical (NLO) chromophores with two parallel and nonconjugated D−π−A units have been synthesized, in which a 9,10-dihydroanthracene is employed as molecular backbone. The measurement results of hyper-Rayleigh scattering (HRS) and UV−vis spectra show that the first molecular hyperpolarizability (β) values of H-shaped chromophores are remarkably increased compared with the corresponding mono-D−π−A unit reference compounds (the enhancements per azo D−π−A unit from 1.2 to 3.0 are observed), without causing a large shift of the absorption band to longer wavelength. Therefore, it gives an available way of solving the trade-off between nonlinearity and transparency in designing NLO chromophores. Furthermore, some main-chain fluoro-containing polyimides embedded with the H-shaped chromophores have also been prepared. The elemental investigation results show that the polyimides exhibit a higher macroscopic nonlinear optical coefficient (d33 = 35.0 to ∼70.2 pm/V), good th...

Two series of fluorine-containing azo dyes containing hexafluoroisopropylidenebis-(4-hydroxybenzene) (B) or 4,4′-(hexafluoroisopropylidene)diphthalicimidine (C) as a backbone connecting the two D-π-A units were synthesized so as to investigate the effects of both the D-π-A units and backbones on the nonlinear optical (NLO) properties of the colourants. Hyper-Rayleigh scattering (HRS) at 1064 nm indicated that the β values of C-containing derivatives were higher than those of B-containing derivatives when the substituents were strongly electron-withdrawing groups. The first hyperpolarizability (β) and static first hyperpolarizability (β0) of the fluorine-containing dyes increased markedly when the difference between the Hammett constants (σ) [Hammett LP. J Am Chem Soc 1937;59:96. Hansch C, Leo A, Taft RW. Chem Rev 1991;91:165.] of the electron-withdrawing and electron-donating groups in the D-π-A units increased, especially when the electron-withdrawing groups in the D-π-A units were strong, such as in the case of nitro and cyan groups. In addition, UV–vis absorption maximum (λmax) of these fluorine-containing azoic dyes were not red shifted compared with the corresponding mono-D-π-A unit compounds.

The new chromophore compounds with NLO properties were prepared by Knoevenagel condensation from formyl or diformyl calix[4]arene and isophorone derivatives in the presence of piperidine and acetic acid, respectively. In these chromophore calix[4]arenes, the ring locked trienes were employed as the conjugation bridge and electron acceptor in D-π-A units. The NMR spectra demonstrated that they existed in a cone conformation and consequently non-conjugated D-π-A units could be oriented at nearly the same direction.

Novel and effective H-shaped chromophores were doped into polymethyl methacrylate (PMMA) to form guest–host polymer thin films. The measurement results of Maker fringe method show that the polymer thin films containing the H-shaped chromophores as a guest exhibit high second harmonic coefficients (d33) compared with other two-dimensional chromophores.

The novel H-shaped chromophores containing two D–π–A units locked parallel to each other are very effective chromophores, because they exhibit much higher first hyperpolarizability ( β ) values than the corresponding mono-D–π–A unit reference compounds and good optical transparency at 532 nm. The first molecular hyperpolarizabilities ( β ) of these H-shaped chromophores were determined via HRS method. In investigating relation between NLO properties and substituent groups on benzene rings, it is found that the β values of H-shaped chromophores vary directly with the difference between the Hammett constants ( σ ) of the electron withdrawing and electron pushing groups in the D–π–A units.

A series of novel second-order nonlinear optical chromophores with two non-conjugated D−π−A units have been synthesized that exhibit much higher first hyperpolarizability (β) values than the corresponding mono-D−π−A unit compounds with a slight red shift.

A series of bis-hydroxyl ethyl azobenzen derivatives were synthesized successfully from N, N-bishydroxyl ethyl aniline and substituted aromatic diazonium chlorides. The hyper-Rayleigh scattering (HRS) method studied their NLO properties. The relation between the first molecular hyperpolarizability values and molecular structures of the chromophores was discussed.

All four chromophores show strong fluorescence emission and are soluble in common organic solvents.

Two tribranched chromophores, 1,3,5-triazine as electron deficient core, 9,9-dimethylfluorene as π -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.

Tribranched chromophores, a 1,3,5-triazine as electron-deficient core, 1,4-phenylenedivinylene as conjugated bridge, 3,4-ethylenedioxythiophene (EDOT) (T1) and triphenylamine (T2) as electron-donating end-groups were successfully prepared. T1 exhibits larger two-photon absorption cross-section than T2, and with an intense blue-shift for λ max in UV, single-photon excited fluorescence (SPEF) and two-photon excited fluorescence (TPEF) spectra.

Four chromophores containing bromo substituents, a ployimide with bromo-containing chromophores, four reference functional polyimides, and fourteen reference chromophores were synthesized for studying effect of bromo substituents on nonlinear optical (NLO) properties of materials and chromophores. The results of hyper-Rayleigh scattering and UV-vis spectra show that static first molecular hyperpolarizability (beta(0)) values of bromo-containing chromophores are 1.24-5.75 times as beta(0) of the corresponding chloro-containing chromophores (Hammett constants sigma of chloro and bromo groups are same) without causing a visible shift of the absorption band to longer wavelength. UV-vis spectra and the results of Maker Fringe method show that the polyimide with chromophores containing bromo substituents exhibits a good optical transparency and a much higher macroscopic nonlinear optical coefficient (d(33) = 20.1 pm/V) than the reference polyimides containing nitro (d(33) = 9.6 pm/V) and cyano (d(33) = 8.9 pm/V) groups in spite of nitro and cyano groups being strong electron acceptors. d(33) of polyimide with chloro-containing chromophores is very small. Therefore, this paper suggests an effective strategy for improving the NLO properties of polymeric materials and chromophores without reducing optical transparency in designing NLO polymers and chromophores. On the basis of quantum chemistry calculations, the reasons of effect of bromo substituents on NLO properties of chromophores and materials were discussed.

The first hyperpolarizabilities (beta) of several ldquoH-shapedrdquo second-order nonlinear optical chromophores measured by hyper-Rayleigh scattering technique exhibit much higher values than those of their monomers with slight absorption red shifting because of intra-molecular interactions.

Wavelength dependent hyper-Rayleigh scattering measurements have been performed by using a fluorescence spectrometer. With this detection strategy, first molecular hyperpolarizability (β) of a dual charge-transfer (H-shaped) chromophore and its monomer have been measured in two-photon resonance range from 670 to 950 nm as well as at off-resonance of 1064 nm. The absorption and resonance hyper-Rayleigh profiles can be simulated reasonably well with a common set of parameters. In addition, both resonance and off-resonance results show that β(0) per chromophore has a remarkable enhancement for the H-shaped molecule as large as 1.7, compared with that of the monomer, which could be ascribed to two physical effects: (1) coherent enhancement of two chromophores and (2) intramolecular dipole-dipole interaction, which was confirmed by their fluorescence-decay behaviors.