Guowei Deng

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.

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.

Facile bromine-termination of nonlinear optical chromophore: remarkable optimization in photophysical properties, surface morphology and electro-optic activity

This paper describes how a small molecular structure modification can enhance the microscopic and macroscopic properties of chromophore. A new chromophore WJ10 is synthesized by applying bromine-termination to the remote donor of WJ6, an existing donor–π–acceptor chromophore. This small molecular change can significantly enhance the photophysical properties of chromophore and generate intriguing inverted solvatochromism in solutions. The absorption intensity of chromophore WJ10 in a guest-host electro-optic polymer film is 40–50% higher than that of the chromophore WJ6, which results in the increase of microscopic first-order hyperpolarizability of WJ10 in guest–host electro-optic (EO) polymer film. DFT calculations was carried out to explain this intriguing photophysical property in both solutions and in films. Bromine-termination also has the influence on macroscopic surface morphology of WJ10 in EO films, making WJ10 more homogeneously dispersed than WJ6. In EO activities, EO coefficient obtained with the WJ10 film is more than two times larger (211 pm V−1) than benchmark value 104 pm V−1 obtained from WJ6. The enhanced electro-optic activity with WJ10 is due to the enhancement of the microscopic hyperpolarizability and the better chromophore alignment in the poling process. This study demonstrates the structure–property relationship in bromine-termination of nonlinear optical chromophore, which can be further explored for the synthesis of new organic EO materials.

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.

Hydrogen-bonded network: An effective approach to improve the thermal stability of organic/polymer electro-optic materials

Binary polymer blends that can form hydrogen-bond networks were prepared and used to fabricate the guest-host organic electro-optic (EO) materials. The hydrogen-bonds network in the solid films of novel guest-host organic EO materials was verified by FT-IR spectra. After corona poling, two kinds of EO films revealed the maximum EO coefficient value (r33) of 19.5 and 30 pm/V at the wavelength of 1310 nm. The EO activity and the order parameter of the chromophores in the poled films both indicated that the hydrogen-bond network has little impact on the motion of the chromophores while poling. These new EO films exhibited better temporal stability after 250 h at 55 and 85 °C compared with the conventional guest-host systems that have the similar or higher Tgs. Moreover, the results also indicated that polymer blends as the host of EO materials can change the dielectric strength of the materials, which directly influence the poling efficiency.

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.