Ningwei Sun

Novel polyamides with fluorene-based triphenylamine: electrofluorescence and electrochromic properties

A series of novel polyamides with fluorene-based triphenylamine units in the backbone were prepared from a newly synthesized diamine monomer, N,N-di (4-aminophenyl)-2-amino-9,9-dimethylfluorene, and various dicarboxylic acids via phosphorylation polyamidation technique. These polyamides were amorphous and exhibited excellent solubility in many polar solvents and could be solution-cast into flexible polymer films. They possess good thermal stability with glass transition temperature in the range of 256–316 °C and 10% weight loss in excess of 500 °C in nitrogen. The dilute N-methyl-2-pyrrolidone (NMP) solutions of these polyamides showed strong UV-vis absorption bands at 334–367 nm and the polyamide derived from 1,4-cyclohexanedicarboxylic acid exhibited fluorescence maximum at 441 nm with quantum yields up to 47.1%. Furthermore, the fluorescence can be effectively switched between “on” and “off” states by applying reduction and oxidation potentials, exhibiting a high contrast ratio (If/If0) of 12.7. The polymer films showed reversible electrochemical oxidation and reduction, enabling an improved stability of electrochromic characteristics with color changing from colorless to green. The anodically electrochromic films had high coloration efficiency (up to 283 cm2 C−1 at 860 nm) and after over 500 cycles the polymer films still exhibited continuous cyclic stability of electrochromism.

Highly stable electrochromic and electrofluorescent dual-switching polyamide containing bis(diphenylamino)-fluorene moieties

Two kinds of electroactive polyamides with bis(diphenylamino)-fluorene units acting as electroactive fluorophores were prepared via condensation polymerization from a novel diamine, N,N′-bis(4-aminophenyl)-N,N′-bis(4-methoxyphenyl)-2,7-diamino-9,9-dimethylfluorene, with cycloaliphatic and aromatic dicarboxylic acids, respectively. These polyamides exhibited excellent solubility in various organic solvents and outstanding thermal stability. Cyclic voltammograms of the polyamide films revealed two reversible redox couples with half-wave potentials at 0.54–0.56 and 0.75–0.78 V, respectively. The polyamide films showed excellent reversible stability of multicolor electrochromic characteristics (colorless-orange-blue) after over 1000 cyclic switches. Compared with the polyamide derived from aromatic dicarboxylic acids, the polyamide derived from cycloaliphatic dicarboxylic acid exhibited strong fluorescence with quantum yield up to 50.2%. Furthermore, the fluorescence could be reversibly modulated by electrochemical redox with superior stability and a high contrast ratio of 152.

Multiple Stimuli-Responsive Fluorescence Behavior of Novel Polyamic Acid Bearing Oligoaniline, Triphenylamine, and Fluorene Groups

Multiple stimuli-responsive fluorescent materials have gained increasing attention for their fundamental investigation and intelligent applications. In this work, we report design and synthesis of a novel polyamic acid bearing oligoaniline, triphenylamine, and fluorene groups, which served as sensitive units and fluorescence emission unit, respectively. The resulting polymer exhibits multiple stimuli-responsive fluorescence switching behavior triggered by redox species, pH, electrochemical, and pressure stimuli. Every fluorescence switching mechanism upon each stimulus was studied in detail. The interactions and energy transfer between sensitive units and emission unit are largely responsible for this fascinating fluorescent switching behavior. This work provides a deep understanding of the optical switching essence upon these stimuli, opening the way for the development of new fluorescent sensing applications.

High-contrast electrochromic and electrofluorescent dual-switching materials based on 2-diphenylamine-(9,9-diphenylfluorene)-functionalized semi-aromatic polymers

Two kinds of electrochromic and photoluminescence-active semi-aromatic polyamide and polyimide were prepared via condensation polymerization from a novel diamine, N,N-di-(4-aminophenyl)-2-amino-9,9-diphenylfluorene, with cycloaliphatic dicarboxylic acid and dianhydride, respectively. These polymers showed excellent solubility and increased thermal stability with 10% weight loss in excess of 450 °C in a N2 atmosphere. Due to the stable electrochemistry and improved solid-state fluorescence properties, the polymer films exhibited repeatable and high-contrast electroswitching in both coloration and emission (ΔT% = 80–85%, Ioff/Ion = 152.1–177.9). Especially, the polyamide still showed excellent electroswitching stability even after hundreds of cycles.

Broad-Range Electrically Tunable Plasmonic Resonances of a Multilayer Coaxial Nanohole Array with an Electroactive Polymer Wrapper

Plasmonic assemblies featuring high sensitivity that can be readily shifted by external fields are the key for sensitive and versatile sensing devices. In this paper, a novel fast-responsive plasmonic nanocomposite composed of a multilayer nanohole array and a responsive electrochromic polymer is proposed with the plasmonic mode appearance vigorously cycled upon orthogonal electrical stimuli. In this nanocomposite, the coaxially stacked plasmonic nanohole arrays can induce multiple intense Fano resonances, which result from the crosstalk between a broad surface plasmon resonance (SPR) and the designed discrete transmission peaks with ultrahigh sensitivity; the polymer wrapper could provide the sensitive nanohole array with real-time-varied surroundings of refractive indices upon electrical stimuli. Therefore, a pronounced pure electroplasmonic shift up to 72 nm is obtained, which is the largest pure electrotuning SPR range to our knowledge. The stacked nanohole arrays here are also directly used as a working electrode, and they ensure sufficient contact between the working electrode (plasmonic structure) and the electroactive polymer, thus providing considerably improved response speed (within 1 s) for real-time sensing and switching.

Rheological behaviour and cure kinetic studies of a trifunctional phenylethynyl-terminated imide oligomer

A phenylethynyl-terminated imide oligomer (PETI)was prepared from a triamine and 4-phenylethynylphthalic anhydride. The oligomer can be used to prepare high performance resin-based composite material via resin transfer moulding due to its low melt viscosity. The cured resin also exhibited excellent thermal stability with 5% weight loss at temperature above 531°C and higher glass transition temperature T g (410°C) than PETI series as a result of the introduction of star-branched units. The rheological properties of the oligomer were measured and numerically fit with the dual Arrhenius model. The curing of the resin was also studied by dynamic and isothermal differential scanning calorimetry measurements. Based on the experimental data, both the curing reaction rate and the curing degree were calculated in the dynamic mode and tested under isothermal conditions.

Porphyrin–poly(arylene ether sulfone) covalently functionalized multi-walled carbon nanotubes: synthesis and enhanced broadband nonlinear optical properties

A novel multi-walled carbon nanotube (MWNT) hybrid was synthesized by covalently attaching a porphyrinated poly(arylene ether sulfone) onto the surface of carbon nanotubes. The polymer functionalized nanotube exhibited excellent solubility in organic solvents, and the weight% of MWNTs in the resulting hybrid was found to be 36%. Considerable fluorescence quenching and shortened fluorescence lifetime were observed in the MWNT hybrid due to the photo-induced electron/energy transfer behavior from porphyrin moieties to MWNTs. Z-scan measurements demonstrated the improved broadband nonlinear optical performance of the MWNT hybrid at both 532 and 1064 nm in nanoseconds, which is attributed to the accumulation effect of nonlinear absorption and scattering, and a remarkable photo-induced electron/energy transfer process. Meanwhile, the MWNT hybrid can be homogeneously dispersed in a polymer matrix, further fabricated into a uniform film with high transparency and ultrafast optical limiting response under femtosecond laser pulses.

A series of organosoluble polyamides with 4-(dimethylamino)triphenylamine Synthesis, thermal and electrochromic properties

A series of novel aromatic polyamides containing 4-(dimethylamino)triphenylamine were prepared via the polycondensation reactions of the newly synthesized dicarboxylic acid, 4,4′-dicarboxy-4″-(dimethylamino)triphenylamine, and various diamines. Introduction of 4-(dimethylamino)triphenylamine units along the polymer chain enhanced the solubility of the polymers. The 10% weight loss temperatures of these polymers ranged from 432°C to 471°C with the char yields more than 63% at 800°C under nitrogen atmosphere. The polymers displayed low oxidation potentials because of the incorporation of dimethylamino at the para position of triphenylamine. Cyclic voltammograms of the polyamide films showed their onset potential around 0.38–0.47 V with color changing from nearly colorless to light blue.

Electrochromic and electrofluorochromic polyimides with fluorene-based triphenylamine

A series of novel polyimides (PIs) based on N,N-di(4-aminophenyl)-2-amino-9,9-dimethylfluorene and various dianhydrides were synthesized. These PIs were amorphous and readily soluble in many solvents. They displayed outstanding thermal stability and high glass transition temperatures (269–374°C). The polymer films showed reversible electrochemical redox and satisfactory electrochromic performance with long-term stability, high coloration efficiency, and acceptable switching times. The PI derived from 1,2,4,5-cyclohexanetetracarboxylic dianhydride exhibited maximum fluorescence at 400 nm with quantum yields up to 28.1%. Furthermore, the fluorescence can be effectively electroswitched between “on” and “off” states, exhibiting a high contrast ratio of 75.

Poly(arylene ether)s based on platinum(II) acetylide complexes: synthesis and photophysical and nonlinear absorption properties

The design and fabrication of nonlinear absorption molecule-embedding solid-state optical power limiting materials are significant but challenging. In the present study, we first report on the synthesis and optical properties of two poly(arylene ether)s incorporating platinum acetylide in the backbones, as well as the fabrication of solid-state optical power limiting materials based on the prepared polymers. The concentrations of platinum acetylide chromophores in the polymer chains were examined to be 19 wt% and 26 wt%, which are the highest levels for non-metal polyyne polymers. Poly(arylene ether)s with platinum acetylide exhibited good mechanical strength, thermal stability, and high glass transition temperature. Investigation of their photophysical behavior revealed that at a high linear transmittance, the polymers showed longer triplet state lifetimes and larger nonlinear absorption coefficients than the corresponding platinum acetylide monomers as a result of the shielding effect. Solid-state monoliths based on platinum acetylide-incorporating poly(arylene ether)s exhibited excellent reverse saturable absorption and optical limiting performance at 532 nm, compared to the optically opaque platinum acetylide chromophore doped polymer monoliths that are formed by severe aggregation.