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).

•Two chromophores had been synthesized and systematically investigated.•Chromophore L1 had smaller energy gap and larger β value than that of chromophore L2.•The r33 value of film-L1/APC is two times than that of the chromophore L2.Two novel chromophores based on the phenoxazine (chromophore L1) or phenothiazine (chromophore L2) donor, and tricyanofuran acceptors linked together via thiophene as the bridges have been synthesized and systematically investigated. Cyclic voltammetry measurements showed that chromophore L1 had smaller energy gap than chromophore L2 due to the stronger electron-donating ability. Moreover, Density functional theory calculations suggested that the β value of chromophore L1 is 17% larger than that of chromophore L2. The doped film containing the chromophore L1 showed an r33 value of 49 pm/V at the concentration of 25 wt% which is two times higher than the EO activity of the chromophore L2 (23 pm/V) and the traditional aryl chromophore (10–20 pm/V). High r33 value, high thermal stability (onset decomposition temperatures higher than 220 °C) suggests the potential use of the new chromophore in nonlinear optical materials.

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.

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.

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 145990). 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.

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.

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.

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.

Two series of novel electro-optic (EO) polycarbonates incorporating two kinds of tricyanopyrroline-based nonlinear optical (NLO) chromophores were designed and synthesized. These new polycarbonates were prepared through the facile copolymerization of diol NLO chromophores and bisphenol A bis(chloroformate), and the successful preparations were demonstrated by 1H NMR and Fourier transform infrared (FT-IR) spectra. These polycarbonates possessed good thermal stabilities and also showed higher glass transition temperatures (Tg) in the range of 156–165 °C. After corona poling, the EO coefficients (r33) of two poled polycarbonates films were up to 52 pm/V (PC-DTCPC-Ph-2) and 46 pm/V (PC-DTCPC-FPh-2) at the wavelength of 1310 nm. The higher Tgs endow the polycarbonates' poled films with good temporal stability of poling-induced dipole alignment, and the resulting poled films of PC-DTCPC-Ph-2 and PC-DTCPC-FPh-2 could retain 95% and 93% of the initial EO activities at 85 °C for more than 500 h respectively.

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).

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.