Chengcheng Peng

Synthesis and optical properties of new fluorinated second-order nonlinear optical copolymers: an attempt toward the balance between solubility and long-term alignment stability

A new fluorinated co-polyarylate (P) was synthesized by interfacial polymerization of 1,1-bis(4-hydroxyphenyl)-1-phenyl-2,2,2-trifluoroethane (BPAPF) and diphenolic acid (DPA) with isophthaloyl chloride (IPC). P1–P3, containing different concentrations of tricyanofuran (TCF) accepter chromophores, were obtained by the esterification reaction between P and chromophore 1 catalyst by DCC and DPTS. The obtained co-polyarylates were characterized and evaluated by UV-Vis, 1H NMR, FT-IR, GPC, DSC and TGA. All the co-polyarylates P1–P3 exhibited excellent thermal stability, film forming ability and good electro-optic (EO) activity. The largest r33 value of the copolymers is 52 pm V−1 at the wavelength of 1310 nm, when the concentration of chromophore 1 is 18 wt%.

Synthesis and properties of a new second-order NLO chromophore containing the benzo[b]furan moiety for electro-optical materials

To further explore the potential application of the benzo[b]furan ring in NLO chromophores, we have designed and synthesized a new chromophore (A) having a 1,1,7,7-tetramethyljulolidine fused furan ring as the electron donor group to systematically investigate the role of benzo[b]furan ring in NLO chromophores. Its corresponding chromophore B using 8-(1-hydroxyhexoxy)-1,1,7,7-tetramethyljulolidine as electron donor group was also prepared for comparison. Upon introducing benzo[b]furan ring at the donor end of chromophore A, a reduced energy gap of 1.14 eV was obtained compared with chromophore B (Ege = 1.28 eV). Furthermore, the macroscopic EO activity of the new chromophores was investigated using guest-host doped polymer films (doping chromophores A or B into amorphous polycarbonate (APC) with a loading density of 20 wt%). The poled films containing chromophore A achieved a maximum EO coefficient (r33) of 52 pm V−1 at 1310 nm, which is larger than the poled films containing chromophore B (r33 = 35 pm V−1). These two chromophores showed excellent thermal stability with onset decomposition temperatures higher than 229 °C. The combined large EO activities and high thermal stability indicates the important role of the benzo[b]furan moiety in the construction of new NLO chromophores.

A study of two thermostable NLO chromophores with different π-electron bridges using fluorene as the donor

Two chromophores C1 and C2 based on a fluorene electron donor with different π-electron bridges and the same electron acceptor have been synthesized and systematically characterized using NMR, MS and UV-vis absorption spectra. The energy gap between the ground state and the excited state and molecular nonlinearity were studied using UV-vis absorption spectroscopy, Density Functional Theory calculations and cyclic voltammetry measurements. The different properties between C1 and C2 were systematically compared. The results showed that C2 had a better performance than C1. The electrooptic coefficient of a poled film containing 25 wt% of C2 doped in amorphous polycarbonate afforded a value of 40 pm V−1 at 1310 nm. In addition, the excellent thermostability of C2 made itself a favourable candidate for practical application.

Synthesis and electro-optic activities of new side-chain polycarbonates containing nonlinear optical chromophores and isolation groups

Dendritic julolidine-based nonlinear optical (NLO) chromophore (JTCFC) possessing isolation group was designed and synthesized to realize effective isolation of NLO chromophores in the polymer backbone. Electro-optic (EO) polycarbonates (PC-JTCFCs) consisting of the dendritic JTCFC and comonomers were prepared through a facile copolymerization strategy. The sufficiently high polymerizability of the dendritic JTCFC, which could be caused by the well-isolation of chromophores and lack of steric effect, afforded the EO polycarbonates with ultra-high molecular weight (Mw up to 145 990). The DSC analysis showed that the EO polycarbonates exhibited similar Tg values (near 150 °C), indicating that the interchromophore interactions are effectively suppressed. The effective isolation of NLO chromophores directly suppressed the dipole–dipole interactions and improved the translation of microscopic hyperpolarizability into macroscopic EO activity. After corona poling, the synthesized EO polycarbonates exhibited a maximum EO coefficient (r33) of 55 pm V−1 at 1310 nm, which was greatly enhanced as compared to the guest–host systems reported previously. Moreover, the prepared EO polycarbonates also possessed good temporal stability, 85% of the initial r33 value of PC-JTCFC-3 could be kept after 500 h at 85 °C.

Microwave-assisted synthesis of novel julolidinyl-based nonlinear optical chromophores with enhanced electro-optic activity

Under microwave (MW) irradiation at a proper temperature, three chromophores (A, B, C) with julolidinyl-based donors and TCF or CF3-Ph-TCF acceptors have been synthesized in high overall yields compared with the conventional heating method. The introduction of a MW heating approach in the synthesis of these chromophores proved to markedly shorten reaction times, reduce by-products and increase the efficiency. The solvatochromic behavior and cyclic voltammetry (CV) measurements suggested that chromophores B and C with stronger acceptors can be more easily polarized with respect to chromophore A. The solvent dependence of the relevant theoretical parameters including dipole moment (μ), first-order polarizability (α), hyperpolarizability (β) and bond-length alternation (BLA) of all chromophores were also studied by DFT calculations. All these chromophores showed good thermal stability and large β values. In an electro-optic (EO) activities test, the guest–host poled polymer A/APC exhibited the highest EO coefficient (r33) of 192 pm V−1 at 1.31 μm. The MW-assisted syntheses and systematic analyses afforded a rational design for NLO chromophores, and provided a new method to optimize the structures of the chromophores to achieve higher r33 values.

Novel NLO-phores containing dihexyl amino benzo[b]thiophene exhibiting good transparency and enhanced electro-optical activity

Two new chromophores (A and B) were synthesized, in which a benzo[b]thiophene moiety was first introduced as a donor group. To investigate the macroscopic EO activity of the new chromophores, guest–host doped polymer films were fabricated by doping chromophores A and B into amorphous polycarbonate (APC). The poled films containing A with a loading density of 20 wt% achieved a maximum EO coefficient (r33) of 42 pm V−1 at 1310 nm, while for the poled films containing B, the r33 value is 75 pm V−1 at 1310 nm. UV-vis spectral absorption of the new chromophores were studied in solutions and films, and chromophores A and B showed a maximum absorption in chloroform of 658 nm and 688 nm, respectively. Compared to the FTC (r33 = 20–50 pm V−1 at 1310 nm, λmax = 685 nm in chloroform) analogues, they exhibited enhanced electro-optical activity together with a high optical gap. This new type of chromophore provided better optimization of the nonlinearity-transparency trade-off.

Research of the optimum molar ratio between guest and host chromophores in binary chromophore systems for excellent electro-optic activity

A series of binary chromophore systems (BCSs) based on electro-optic (EO) polymers P1–P5 and guest chromophores C1 and C2 were designed and prepared. The poled films of these BCSs showed large EO coefficients (r33 = 57–160 pm V−1), which were much higher than the sum of their individual components. The optimum molar ratio (OMR) between guest and host chromophores was first systematically explored by changing their molar ratios (Ng : Nh) in the following BCSs: (1) C1/P2; (2) C1/P4; (3) C2/P1; (4) C1/P5. Meanwhile, the influence of the types of the chromophores and the polymer main chains on the OMR was also studied. Finally, these results indicated that the BCSs showed the greatest r33 growth rates when the Ng : Nh was 1 : 1. Hence, the OMR in BCS was 1 : 1 and the types of the chromophores and the polymer main chains were found to have little influence on the OMR. At the OMR, the r33 values were even 2.1 times of the sum of their individual components. We give a model for this phenomenon. The research of OMR in BCSs provided a promising way to further improve the EO coefficients.

Synthesis and electro-optic properties of the chromophore-containing NLO polyarylate polymers

Base on the same two monomers, diphenolic acid (DPA) and isophthaloyl chloride (IPC), three chromophore-containing nonlinear optical (NLO) polyarylate polymers were prepared. A tricyanofuran (TCF)-acceptor type chromophore group was in main-chain (mPAR-chr1), side-chain (sPAR-chr1) and side-chain with a 1,1-bis(4-hydroxyphenyl)-1-phenyl-2,2,2-trifluoroethane (BPAPF) group (sPAR-F-chr1), respectively. The obtained polymers were characterized and evaluated by UV-Vis, 1H NMR, DSC and TGA. All the polymers exhibited good electro-optic (EO) activity. The relationship between EO coefficients (r33) and the chromophore concentration of the three polymers were also characterized and discussed. There were no obvious differences found in EO activity between mPAR-chr1 and sPAR-chr1 polyarylates with the same chromophore. The fluorinated block polyarylate sPAR-F-chr1 has the largest r33 value in these three polyarylates which is 52 pm/V at the wavelength of 1310 nm (which is almost twice the r33 value of normal polymers contained the same chormophore at the same content), when the concentration of chromophore 1 is 18wt.%. 85% of the r33 value was retained in the sPAR-F-chr1 after being heated at 85°C for 600 hours. The polymer sPAR-F-chr1, with good solubility, high Tg (above 200 °C) and side functional group at the same time, may probably be a practical NLO material. These properties make the new polyarylates have potential applications in EO devices such as EO modulators and switches.