A donor-acceptor-π-acceptor (D-A-π-A)-type organic dye (DTN-1) incorporating a pyrido[3,4-b]pyrazine (PP) unit with the pyridyl N atom adjacent to the anchoring group has been synthesized for use in dye-sensitized solar cells (DSSCs). The maximum absorption wavelength of DTN-1 was clearly red-shifted compared with dye DT-1, based on PP unit with the pyridyl N atom adjacent to the donor group. However, this change of structure has a negative effect on photovoltaic performances, and devices made with DTN-1 only reached a power conversion efficiency of 6.10 % under AM1.5G irradiation compared with 8.57 % achieved by DT-1. Density functional theory calculations suggest that DTN-1 has a smaller oscillator strength, which is connected to its relatively low light-harvesting efficiency. In addition, the results of electrochemical impedance spectroscopy (EIS) reveal that charge recombination in DSSCs based on DTN-1 is more than that in the counterpart DT-1, thus leading to a lower open-circuit voltage (V_oc).

Compared with traditional one-photon fluorescence imaging, two-photon fluorescence imaging techniques have shown advantages such as increased penetration depth, lower tissue autofluorescence, and reduced photo­damage, and therefore are particularly useful for imaging tissues and animals. In this work, the design and synthesis of two novel DPP-based compounds with large two-photon absorption (2PA) cross-sections (σ ≥ 8100 GM) and aggregation-induced emission (AIE) properties are reported. The new compounds are red/NIR emissive and show large Stokes shifts (Δλ ≥ 3571 cm⁻¹). 1,2-Distearoyl-sn-glycero-3-phosphoethanol amine-N-[maleimide(polyethylene glycol)-2000 (DSPE-PEG-Mal) is used as the encapsulation matrix to encapsulate DPP-2, followed by surface functionalization with cell penetrating peptide (CPP) to yield DPP-2-CPP nanoparticles with high brightness, good water dispersibility, and excellent biocompatibility. DPP-2 nanoparticles have been used for cell imaging and two-photon imaging with clear visualization of blood vasculature inside mouse ear skin with a depth up to 80 μm.

Two organic donor–acceptor–π–acceptor (D-A-π-A) sensitizers (AQ and AP), containing quinoxaline/pyrido[3,4-b]pyrazine as the auxiliary acceptor, have been. Through fine-tuning of the auxiliary acceptor, a higher designed and synthesized photoelectric conversion efficiency of 6.02 % for the AQ-based dye-sensitized solar cells under standard global AM1.5 solar conditions was achieved. Also, it was found that AQ-Pt/TiO₂ photocatalysts displayed a better rate of H₂ evolution under visible-light irradiation (420 nm<λ<780 nm) because of the stability of the oxidized states and the lower rates of electron recombination. Importantly, sensitizers AQ and AP-Pt/TiO₂ showed strong photocatalytic activity during continuous light soaking for 10 h with methanol as the sacrificial electron donor. Additionally, the processes of their intermolecular electron transfer were further investigated theoretically by using time-dependent DFT. The calculated results indicate that the auxiliary acceptor plays the role of an electron trap and results in broad spectral responses.

Three new metal-free dyes with a 5,6-bis(octyloxy)benzo[c][1,2,5]thiadiazole core (DOBT-I–III) have been designed and synthesized for use as DSSCs. Their absorption properties and electrochemical and photovoltaic performances have been investigated systematically. The DSSCs based on DOBT-I–III show high open-circuit voltages (V_oc) of 829, 818, and 784 mV, respectively. Of the three dyes, DOBT-III, which contains a thiophene-bridging linker, exhibits the best photovoltaic performance: a short-circuit photocurrent density (J_sc) of 12.74 mA cm^–2 and a fill factor (FF) of 0.73, which corresponds to an overall conversion efficiency of 7.29 % under standard global AM 1.5 solar conditions.

Room temperature molten salt 1-methyl-3-(trimethylsilyl)methyl-imidazolium iodide (MSII) was used for iodide sources in dye-sensitized solar cells with an organic sensitizer 2-cyano-3-[5-[4-[3-[4-(4-(N,N-bis(4-methoxyphenyl)amino)phenyl)phenyl]-2,5-di-n-butyl-pyrrolo[3,4-c]pyrrole-1,4-dione]phenyl]furan-2-yl] acrylic acid (DPP-I) as light harvester. With an optimized electrolyte (MSII:I₂:BI:GuNCS24:2:2:0.4, BI and GuCNS are short for benzimidazole and guanidine thiocyanate, respectively), photovoltaic parameters (J_sc, V_oc, and ff) of device are 8.97 mA·cm⁻², 600 mV and 0.61, respectively, yielding a maximum overall photo-to-energy conversion ef?ciency (η) of 3.23%. And then the charge-transfer mechanism of devices was deeply analyzed with electrochemical impedance spectroscopy (EIS) in the dark.

Two new benzotriazole-bridged sensitizers are designed and synthesized (BTA-I and BTA-II) containing a furan moiety for dye-sensitized solar cells (DSSCs). Two corresponding dyes (BTA-III and BTA-IV) with a thiophene spacer were also synthesized for comparison. All of these dyes performed as sensitizers for DSSCs, and the photovoltaic performance data of these benzotriazole-bridged dyes showed a high open-circuit voltage (V_oc: 804–834 mV). Among the four dyes, DSSCs based on BTA-II, with a furan moiety and branched alkyl chain, showed the highest V_oc (834 mV), a photocurrent density (J_sc) of 12.64 mA cm⁻², and a fill factor (FF) of 0.64, corresponding to an overall conversion efficiency (η) of 6.72 %. Most importantly, long-term stability of the BTA-I, BTA-II, BTA-III, BTA-IV-based DSSCs with ionic-liquid electrolytes under 1000 h light-soaking was demonstrated, and BTA-II exhibited better photovoltaic performance of up to 5.06 % power conversion efficiency.

A series of new push–pull organic dyes (BT-I–VI), incorporating electron-withdrawing bithiazole with a thiophene, furan, benzene, or cyano moiety, as π spacer have been synthesized, characterized, and used as the sensitizers for dye-sensitized solar cells (DSSCs). In comparison with the model compound T1, these dyes containing a thiophene moiety between triphenylamine and bithiazole display enhanced spectral responses in the red portion of the solar spectrum. Electrochemical measurement data indicate that the HOMO and LUMO energy levels can be tuned by introducing different π spacers between the bithiazole moiety and cyanoacrylic acid acceptor. The incorporation of bithiazole substituted with two hexyl groups is highly beneficial to prevent close π–π aggregation, thus favorably suppressing charge recombination and intermolecular interaction. The overall conversion efficiencies of DSSCs based on bithiazole dyes are in the range of 3.58 to 7.51 %, in which BT-I-based DSSCs showed the best photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 81.1 %, a short-circuit photocurrent density (J_sc) of 15.69 mA cm⁻², an open-circuit photovoltage (V_oc) of 778 mV, and a fill factor (ff) of 0.61, which correspond to an overall conversion efficiency of 7.51 % under standard global AM 1.5 solar light conditions. Most importantly, long-term stability of the BT-I–III-based DSSCs with ionic-liquid electrolytes under 1000 h of light soaking was demonstrated and BT-II with a furan moiety exhibited better photovoltaic performance of up to 5.75 % power conversion efficiency.

Five new multi-branched two-photon absorption triazine chromophores (T1–T5) with different donor strength, conjugation length, and direction of charge transfer have been designed and synthesized. The one-photon fluorescence, fluorescence quantum yields, and two-photon properties have been investigated. The two-photon absorption (2PA) cross sections measured by the open aperture Z-scan technique were determined to be 447, 854, 1023, 603, and 766 GM for T1, T2, T3, T4, and T5, respectively. This result indicates that their 2PA cross section values (σ) increase with increasing electron-donating strength of the end group, extending the conjugation length of the system, and introducing electron-withdrawing perfluoroalkyl as side groups to the end donor. In addition, the σ value of T5 is also larger than that of T1, which provides evidence that the σ value is relative to the direction of charge transfer (from the ends to the center of the molecule or from the center to the ends). Moreover, significant enhancement of the two-photon absorption cross section was achieved by introducing a thiophene moiety to a conjugated CC bond. At the same time, the optical limiting behavior for these chromophores was studied by using a focused 800 nm laser beam with pulses of 140 fs duration. It was found that these molecules also exhibit good optical limiting properties. These initial results clearly demonstrate that multi-branched triazine chromophores are a highly suitable class of two-photon absorbing materials.

In this work, we have developed a new class of aggregation-induced emission (AIE) active compounds, in which three electron-donating diphenylamine, phenothiazine, or carbazole groups are connected to the 1, 4-positions of the benzene through bis(α-cyano-4-diphenylaminostyryl) conjugation bridges to form three triarylamine quadrupolar derivatives (3 a–c). Their one- and two-photon absorption properties have been investigated. The two-photon absorption (2PA) cross sections measured by the open-aperture Z-scan technique were determined to be 1016, 1484, and 814 GM for 3 a–c, respectively. From this result, the high 2PA properties of these molecules are attributed to the extended π system and enhanced intramolecular charge transfer from the starburst triarylamine to the cyano group. Moreover, cyano-substituted diphenylamine styrylbenzene (CNDPASB)-based compounds are very weakly fluorescent in THF, but their intensities increase by almost 230, 70, and 5 times, respectively, in water/THF (v/v 90 %) mixtures, in which they exhibit strongly enhanced red, orange, and deep yellow fluorescence emissions, respectively. This result indicates that the intramolecular vibration and rotation of these dyes is considerably restricted in nano-aggregates formed in water, leading to significant increases in fluorescence. It was found that the color tuning of the CNDPASB-based compounds could be conveniently accomplished by changing the starburst triarylamine donor moiety. Multilayer electroluminescence devices with TPBI (2,2′,2′′-(benzene-1,3,5-triyl)-tri(1-phenyl-1H-benzimidazole)) electron-transporting layers have been made, with 3 a and 3 c as a non-doping red–yellow emitter. The preliminary results for these multilayer devices show a maximum efficiency of 0.25 %, and electroluminescence (EL) wavelengths around 568 nm. The excellent 2PA and AIE properties of these compounds make them potential materials for biophotonic applications.

Two new linear and hyperbranched conjugated polymers P1 and P2 have been synthesized by Sonogashira coupling reaction, in which the main chain consists of bithiazole moieties as electron acceptors and triphenylamino groups as donors. The conjugated polymers were characterized by TGA, UV–vis absorption, fluorescence emission, electrochemical cyclic voltammetry, and two-photon absorption measurements. They exhibited excellent solubility in organic solvents and high thermal stability (5% of weight loss at 299 °C). The two-photon absorption cross sections (σ) measured by the open aperture Z-scan technique using 140 femtosecond (fs) pulse were determined to be 1014 and 552 GM per repeating unit for P1 and P2, respectively. This result shows that the σ of linear conjugated P1 is higher than that of hyperbranched P2, indicating that the linear polymer offers better intramolecular charge transfer ability. In THF, P1 and P2 exhibit intense frequency up-converted fluorescence under the excitation of 140 fs pulses at 800 nm with the peaks located at 580 and 548 nm, respectively. Meanwhile, the optical limiting behaviors for the polymers were studied by using a focused 800 nm laser beam of 140 fs duration. It was found that these polymers also exhibit good optical-limiting properties and make them potential candidates for optical limiters in the photonic fields. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

A novel hyperbranched polyyne (hb-DPP) with triphenylamine as the core, 2,5-dioctylpyrrolo [3,4-c]pyrrole-1,4 (2H,5H)-dione (DPP) as the connecting unit has been designed and synthesized by Glaser-Hay oxidative coupling reaction, which was characterized by IR, NMR, UV-vis, FL, and GPC. The polymer exhibits high molecular weight (M_w up to ∼6.55 × 10⁴ Da) and is readily soluble in common organic solvents such as toluene, chloroform, tetrahydrofuran, N,N-dimethyl formamide and so on. The one- and two-photon absorption (TPA) properties have been investigated. The TPA cross section of the polymer was measured by open-aperture Z-scan experiment using 140 femtosecond (fs) pulse, and the TPA cross section for hb-DPP was determined to be 579 GM per repeating unit at wavelength of 800 nm. In tetrahydrofuran, hb-DPP exhibits intense frequency up-converted fluorescence with the peak located at 584 nm under the excitation of 800 nm fs pulses. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4400–4408, 2009

Novel polyphenylacetylene (P1) containing naphthalimides units in the side chain was designed and synthesized. The structure and properties of the polymer were characterized and evaluated by IR, NMR, UV, and PL. The measurements of sensing behavior to various halide anions, that is, F⁻, Cl⁻, Br⁻, and I⁻, reveal that the polymer is a ratiometric fluorescent chemosensors for fluoride ion. The polymer sensor shows spectral shifts and intensity changes in the presence of fluoride, in a wavelength-ratiometric and -colorimetric manner, which can detect fluoride concentrations in range of 10–100 μM at visible wavelengths. The obvious colorless-to-yellow color change and blue-to-orange emission color change on the addition of fluoride ion are easily observed by naked eyes. It provides a feasible way to construct a ratiometric fluorescent chemosensors for fluoride ion. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1544–1552, 2009

Three new poly(N-vinylcarbazole) (PVK)-based copolymers containing N-(n-butyl)-N-ethyl-1,6,7,12-tetra-(4-tert-butyl-phenoxy)-3,4,9,10-perylene tetracarboxylic bisimides were successfully synthesized by partially formylated by the standard Vilsmeier reaction, and the formyl groups of high reactivity are condensed with cyanoacetylated perylene to afford PVK-based polymers. The copolymers containing different percentage of perylene were obtained through the percentage of cyanoacetylated perylene unit being controlled by the initial feed ratio. The structures and properties of three copolymers were characterized and evaluated by FT-IR, NMR, UV–vis, FL spectroscopy, gel permeation chromatography, and thermogravimetric analysis measurements. The polymers were highly soluble in conventional solvents such as toluene, CHCl₃, THF, DMF etc., and they were thermally stable up to 442–445°C. Three copolymers have emission spectra with characteristic features of the perylene unit, and fluorescence quantum yields of polymers are higher than that of perylene bisimide, which may be caused by singlet–singlet energy transfer from PVK backbone to perylene in the polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008