Chao-Zhi Zhang

Significant effect of bromo substituents on nonlinear optical properties of polymer and chromophores.

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.

p-Nitrophenylazo Calix[4]arenes, Synthesis, Monolayers and NLO-properties

The mono, bis, tris and tetrakis (p-nitrophenyl)azo calix[4]arenes (1, 2, 3 and 4) with NLO properties are synthesized by the diazo-coupling of calix[4]arene with p-nitrophenyl diazonium. HRS measurements at 1064 nm indicate that (p-nitrophenyl)azo calix[4]arenes have higher second-order hyperpolarizability β values than the corresponding reference compound 4-(4-nitrophenylazo)-2,6-dimethylphenol, without red shift of the charge transfer band. The bis and tris (p-nitrophenyl)azo calix[4]arenes (2, 3) without hydrophobic alkyl chains can form stable Langmuri monolayers at the air/water interface because of arene π–π stacking.

Theoretical Study of Nonlinear Optical Properties of “Parallel Connection” Chromophores Containing Parallel Nonconjugated D-π-A units

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-photon resonant hyperpolarizability of an H-shaped molecule studied by wavelength-tunable hyper-Rayleigh scattering

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.

Electric response of a metal-molecule-metal junction to laser pulse by solving hierarchical equations of motion

We have combined the quantum dissipative theory and the time dependent density functional theory to perform the first principle calculation of laser induced quantum dynamical electron transport through a molecule weak bridged to two electrodes. The formalism of hierarchical equations of motion based on non-equilibrium Greens function theory has been taken in this work. Numerical simulations of optical absorption spectra of benzene, laser induced transient current without and with bias, charge pumping effect, as well as the spectrum analysis from the current in Au-benzene-Au molecular junction are presented and discussed.

NONLINEAR OPTICAL PROPERTIES OF NOVEL AND EFFECTIVE H-SHAPED CHROMOPHORES CONTAINING THREE PARALLEL AND NON-CONJUGATED D-π-A UNITS

H-shaped chromophores containing three parallel non-conjugated D-π-A units are effective chromophores with high hyperpolarizability and good optical transparency. The semi-empirical methods ZINDO, AM1, MNDO and PM3 were employed to study the effect of strength of acceptors and donors, and steric repulsion between substituents on static first hyperpolarizabilities (β0) and enhancements of β0 of the H-shaped chromophores. The results show that the H-shaped chromophore would exhibit the largest β0 and/or the largest enhancement of β0 of the chromophore when combination of a donor (D) and an acceptor (A) in a D-π-A unit is suitable.

Synthesis and crystal structure of 2-(4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropan-2-ol

The title compound 2-(4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropan-2-ol was synthesized by the reaction of phenol with hexafluoroacetone using mesitylene as solvent and. methanesulfonic acid as catalist. The structure is determined by X-ray structure analysis. Two kinds of strong intermolecular hydrogen bonds O(Alk)-H···O(Ar)and O(Ar)-H···O(Alk) are formed in crystal. These hydrogen bonds connect the molecules into two-dimensional layers. Based on theoretical calculations of the electronic structure of the title compound, its application in fluoro-containing materials is predicted. The title compound may be employed to synthesize many organic fluoro-containing polymers, because alcoholic hydroxyl and phenolic hydroxyl are easily deprotonated.

Theoretical Study of Effect of the Number of N,N-dimethyl-4-nitroaniline Units in Novel “Parallel Connection” Chromophores on Its Nonlinear Optical Properties

Design of “parallel connection” chromophores could give a way of acquiring effective chromophores. The semiempirical method ZINDO was employed to study relationship between static first hyperpolarizabilities of “parallel connection” chromophores and the number of parallel nonconjugated N,N-dimethyl-4-nitroaniline (DMNA) units in the chromophore. The results show that the chromophore containing three parallel non-conjugated DMNA units exhibits the highest static first hyperpolarizability, which is 1.8 times that of chromophore DMNA. However, static first hyperpolarizabilities of the chromophores containing four or five DMNA units are very small. The absorption maximum wavelength (𝜆max) of “parallel connection” chromophores is remarkably shorter (34.9 nm–38.1 nm) than that of 1DMNA. Therefore, the “parallel connection” chromophore containing three DMNA units would be an effective chromophore with a large first hyperpolarizability and a good optical transparency. It could give a useful suggestion for designing effective chromophores containing parallel non-conjugated D-π-A units.

Crystal structure and optoelectronic properties of antiaromatic compound 3,4,9,10-tetrahydrodicyclopenta[ cd,lm ]perylene

An antiaromatic compound 3,4,9,10-tetrahydrodicyclopenta[cd,lm] perylene, was synthesized by a coupling reaction. Its crystal structure was determined by X-ray diffraction. Crystal structures shows that the antiaromatic compounds are aggregated to J-aggregation materials. It further results ultrafast charge separation at organic interface and electron transfer in the aggregation materials. UV-vis spectrum shows that title compound has a broad UV-vis light absorbance at the wavelength range from 250 to 470 nm and a 2.67 eV energy gap value between the highest occupied and the lowest unoccupied molecular orbital energy levels.

THEORETICAL STUDY OF MACROSCOPIC OPTICAL NONLINEARITIES OF "PARALLEL CONNECTION" CHROMOPHORES CONTAINING PNA UNITS

The semi-empirical method ZINDO was employed to study relationship between macroscopic optical nonlinear parameter μβ/MW (where μ is the dipole moment, β is the first hyperpolarizability, and MW is molecular weight) and the number of parallel non-conjugated D-π-A units in a chromophore. The computational results show that macroscopic optical nonlinear parameter μβ/MW value increases remarkably from 1.64 to 2.53 with increasing the number of parallel and non-conjugated p-Nitroaniline (PNA) units in a chromophore from 1 to 3. Then the μβ/MW value decreases rapidly from 2.53 to 0.43 with increasing the number of PNA units in a chromophore from 3 to 5. It suggests that design of chromophores containing two or three parallel non-conjugated D-π-A units would be an effective strategy for increasing the first hyperpolarizability and macroscopic optical nonlinearity of designed NLO materials.