Shuhui Bo

Synthesis of novel nonlinear optical chromophore to achieve ultrahigh electro-optic activity

A new diene-conjugated chromophore WJ1 was synthesized with high yield of 36% through an H-bonding induced Vilsmeier reaction. By simple guest-host doping, a large electro-optic efficiency of 337 pm V(-1) at 1310 nm and excellent temporal stability at 75 °C have been achieved in poled films of WJ1/APC with a high loading density of 40 wt%.

Enhanced electro-optic coefficient (r33) in nonlinear optical chromospheres with novel donor structure

The synthesis and characterization of new push-pull chromophores A and B, from tricyanofuran (TCF) electron withdrawing and various electron donating moieties, have been demonstrated to compare the roles of donors in electro-optic performance. The crystal structure analyses of the intramolecular hydrogen bond, molecular coplanarity and π–π interactions reveal that A forms cross-stacking, while B forms antiparallel dimer packing, which indicates weaker intermolecular interactions of A than B. Also, the photophysical properties, solvatochromic behavior and Density Functional Theory (DFT) calculations were also investigated. In electro-optic activities, the doped films-A containing chromophore A display an r33 value of 36 pm V−1 at the saturated doping concentration of 40 wt%, while the doped films-B containing B show a maximum r33 value of 16 pm V−1 at the saturated concentration of 25 wt%. High loading density and high r33 value indicate that the chromophore A with julolidinyl-based donor can efficiently reduce the interchromophore electrostatic interactions and enhance the macroscopic optical nonlinearity, showing that chromophore A with julolidinyl-based donor has promising applications in nonlinear optical (NLO) materials.

One-step synthesis of highly water-soluble LaF3: Ln3+ nanocrystals in methanol without using any ligands

Water-soluble infrared-to-visible fluorescent LaF(3) nanocrystals doped with different lanthanide ions (Er(3+)/Yb(3+), Eu(3+), Nd(3+), Tb(3+)) have been synthesized in methanol without using any ligands. These nanocrystals are easily dispersed in water, producing a transparent colloidal solution. The colloids of the Er(3+)/Yb(3+), Eu(3+), Nd(3+), Tb(3+) doped nanocrystals exhibit strong luminescence in the visible and near-infrared spectral regions.

Nonlinear optical chromophores containing a novel pyrrole-based bridge: optimization of electro-optic activity and thermal stability by modifying the bridge

Three novel second order nonlinear optical chromophores based on julolidinyl donors and tricyanovinyldihydrofuran (TCF) acceptors linked together via modified pyrrole π-conjugation (chromophores A and B) or thiophene moieties (chromophore C) as the bridges have been synthesized and systematically characterized. In particular, the pyrrole moiety bridge has been modified with the electron withdrawing group (–Br, –NO2) substituted benzene ring. The introduction of side phenyl groups to chromophores A and B can increase the thermal and chemical stability and reduce dipole–dipole interactions so as to translate their hyperpolarizability (β) values into bulk EO performance more effectively than chromophore C. Moreover, DFT calculations suggested that the additional electron withdrawing groups in chromophores A and B could increase the β value compared to that of chromophore D without substituted phenyl groups, and they showed different influences on the solvatochromic behavior, thermal stability, and electro-optic activity of the chromophores. EO responses (r33 values) of guest–host polymers containing pyrrole-bridged chromophores were reported. Incorporation of chromophores A and B into APC provided large electro-optic coefficients of 86 and 128 pm V−1 at 1310 nm with a high loading of 30 wt%. Film-C/APC containing 25 wt% of chromophore C provides an EO coefficient of 98 pm V−1.

Synthesis and optical nonlinear property of Y-type chromophores based on double-donor structures with excellent electro-optic activity

New Y-type chromophores FTC-yh1 and FTC-yh2 containing bis(N,N-diethyl)aniline as a novel electron-donor, thiophene as a π-conjugated bridge and tricyanofuran (TCF) as an acceptor have been synthesized and systematically investigated in this paper. Density functional theory (DFT) was used to calculate the HOMO–LUMO energy gaps and first-order hyperpolarizability (β) of these chromophores. These chromophores showed better thermal stability with their decomposition temperatures all above 240 °C. Most importantly, the high molecular hyperpolarizability of these chromophores can be effectively translated into large electro-optic (EO) coefficients (r33) in poled polymers. The doped film-A containing 25 wt% chromophore FTC-yh1 displayed a value of 149 pm V−1 at 1310 nm, and the doped film-B containing FTC-yh2 showed a value of 143 pm V−1 at the concentration of 25 wt%. These values are almost four times higher than the EO activity of usually reported traditional single (N,N-diethyl)aniline nonlinear optical (NLO) chromophores FTC. High r33 values indicated that the double donors of the bis(N,N-diethyl)aniline unit can efficiently improve the electron-donating ability and reduce intermolecular electrostatic interactions, thus enhancing the macroscopic EO activity. These properties, together with the good solubility, suggest the potential use of the new chromophores as advanced material devices.

Comparison of nonlinear optical chromophores containing different conjugated electron-bridges: the relationship between molecular structure-properties and macroscopic electro-optic activities of materials

In electro-optic (EO) materials, realization of large EO coefficients for organic EO materials requires the simultaneous optimization of chromophore first hyperpolarizability, acentric order, molecular shape etc. As these parameters are complicatedly inter-related, thorough analyses are required to understand the dependence of macroscopic EO activity upon chromophore structure and property. Herein, we presented the synthesis of three chromophores containing different conjugated electron-bridges by acidic and alkaline formylation. Electron-rich moieties thiophene and formyl-thiophene in the different positions of chromophores played the different roles of electron-bridge, site-isolator and electron-isolator, generating intriguing property variations of electron distribution of push–pull structure, intramolecular charge-transfer, solvatochromism, microscopic hyperpolarizability and related density functional theory calculation results. In addition these molecular structure–property relationships were rationally related to the EO activities to understand the impact of microscopic molecular property on macroscopic EO activities of materials.

Synthesis of novel nonlinear optical chromophores: achieving excellent electro-optic activity by introducing benzene derivative isolation groups into the bridge

Three novel second order nonlinear optical (NLO) chromophores based on julolidinyl donors and tricyanofuran (TCF) acceptors linked together via modified polyene π-conjugation with rigid benzene derivative steric hindrance groups (chromophore CL1 and CL2) or unmodified polyene π-conjugation (chromophores CL) moieties as the bridges have been synthesized in good overall yields and systematically characterized. Density functional theory (DFT) was used to calculate the HOMO–LUMO energy gaps and first-order hyperpolarizability (β) of these chromophores. Besides, to determine the redox properties of these chromophores, cyclic voltammetry (CV) experiments were performed. Compared with CL, after introducing benzene derivative steric hindrance groups into the bridge, chromophores CL1 and CL2 had good thermal stabilities with high thermal decomposition temperatures which were 32 °C and 24 °C higher than chromophore CL, respectively. Most importantly, the introduction of rigid steric hindrance groups can effectively reduce dipole–dipole interactions to translate their relatively small β values into bulk high EO activities. By doping chromophores CL, CL1 and CL2 with a high loading of 45 wt% in APC, EO coefficients (r33) of up to 121, 197 and 202 pm V−1 at 1310 nm can be achieved, respectively. The r33 values of new chromophores CL1 and CL2 were about 1.6 times of chromophore CL. The high r33 value, good thermal stability and high yield suggest the potential use of the new chromophores in an nonlinear optical area.

A systematic study of the structure–property relationship of a series of nonlinear optical (NLO) julolidinyl-based chromophores with a thieno[3,2-b]thiophene moiety

A series of nonlinear optical (NLO) chromophores a–d bearing thieno[3,2-b]thiophene (TT) as the conjugated bridge or the lateral moiety have been synthesized and investigated. These chromophores display the same julolidinyl-based electron donor, but different electron acceptors (i.e., 2-dicyanomethylene-3-cyano-4-methyl-2,5-dihydrofuran, TCF, or malononitrile). The solvatochromic behavior, thermal stability and electrochemical properties were evaluated to study the structure–property relationships. The solvent dependence of dipole moment (μ), static polarizability (α), hyperpolarizability (β) and bond length alternation (BLA) of all chromophores was demonstrated by density functional theory (DFT) calculations. Upon using the D–A–π–A structure, the blue-shifted phenomenon and substantially enhanced microscopic NLO properties of chromophore d were obtained. The electrooptic coefficient (r33) of chromophore a (94 pm V−1 at 1.31 μm) was four times higher than that of chromophore b (∼20 pm V−1), while the calculated hyperpolarizability (β) of chromophore b was five times larger with respect to chromophore a. All the results demonstrated that the TT unit is a highly efficient conjugated bridge, and it has some electronical and sterical effects on macroscopic electrooptic (EO) activity when it is used as the lateral moiety. Guidelines can be proposed for the design of a new series of guest–host polymers including julolidinyl-based chromophores with a TT moiety, which could be useful in organic EO device fabrication.

Comparison of second-order nonlinear optical chromophores with D–π–A, D–A–π–A and D–D–π–A architectures: diverse NLO effects and interesting optical behavior

Four second-order nonlinear optical chromophores with D–π–A, D–A–π–A and D–D–π–A architectures have been synthesized and systematically characterized. Chromophores A and C have been synthesized with an additional acceptor (–CN) or donor group (thiophene) on the π bridge, termed the D–A–π–A and D–D–π–A configurations. D–π–A structural chromophores B and D were chosen as reference compounds for comparison. The results show that incorporation of the –CN group could increase poling efficiency possibly due to reduced intermolecular dipole–dipole interactions which results in comparable r33 values (48 pm V−1). An r33 value of 45 pm V−1 was obtained for the film C/APC suggesting significant site isolation. Compared with the D–π–A structural chromophores B and D, chromophores A and C demonstrated similar or enhanced NLO effects and better optical transparency.

Auxiliary donor for tetrahydroquinoline-containing nonlinear optical chromophores: enhanced electro-optical activity and thermal stability

A series of chromophores FTC, L1 and L2 have been synthesized based on three different types of electron donors, including diethylaminophenyl, tetrahydroquinolinyl and N-(4-dimethylaminophenyl) tetrahydroquinolinyl groups respectively, with the same thiophene bridges and strong tricyanovinyldihydrofuran (TCF) acceptors. In particular, the donor part of the chromophore L2 was modified with an additional donor N-(4-dimethylaminophenyl) substituent, resulting in enhanced thermal stability and electro-optic activity. Cyclic voltammetry measurements showed that chromophore L2 had a smaller energy gap than chromophore L1 due to the additional donor. Moreover, density functional theory calculations suggested that the molecular quadratic hyperpolarizability (μβ) value of chromophore L2 is 29% and 44% larger than that of chromophores L1 and FTC, respectively. The doped film containing the chromophore L2 showed an r33 value of 100 pm V−1 at the concentration of 25 wt% which is much higher than the EO activity of the chromophore L1 (57 pm V−1) and two times higher than that of the traditional chromophore FTC (39 pm V−1).