Hyperbranched Copolymers Based on Glycidol and Amino Glycidyl Ether: Highly Biocompatible Polyamines Sheathed in Polyglycerols

Functional hyperbranched polyglycerols (PGs) have recently garnered considerable interest due to their potential in biomedical applications. Here, we present a one-pot synthesis of hyperbranched PGs possessing amine functionality using a novel amino glycidyl ether monomer. A Boc-protected butanolamine glycidyl ether (BBAG) monomer was designed and polymerized with glycidol (G) through anionic ring-opening multibranching polymerization to yield a series of hyperbranched P(G-co-BBAG) with controlled molecular weights (4800-16700 g/mol) and relatively low molecular weight distributions (1.2-1.6). The copolymerization and subsequent deprotection chemistry allow the incorporation of an adjustable fraction of primary amine moieties (typically, 5-20% monomer ratio) within the hyperbranched PG backbones, thus providing potentials for varying charge densities and functionality in PGs. The copolymerization kinetics of G and BBAG was also evaluated using a quantitative in situ 13C NMR spectroscopic analysis, which revealed gradient copolymerization between the comonomers. The free amine groups within the deprotected P(G-co-BAG) copolymer were further utilized for a facile conjugation chemistry with a model molecule in a quantitative manner. Furthermore, the superior biocompatibility of the prepared P(G-co-BAG) polymers was demonstrated via cell viability assays, outperforming many existing polyamines possessing relatively high cytotoxicity. Taken together, the biocompatibility with facile conjugation chemistry of free amine groups sheathed within the framework of hyperbranched PGs holds the prospect of advancing biological and biomedical applications.close0

Small molecules based on 6,7-difluoroquinoxaline and thieno[3,2-b]thiophene for solution-processed solar cells

Fluorinated quinoxaline-based small molecules, SM1, SM2, and SM3, were developed as the donor materials for photovoltaic cells. The small molecules containing a 2,3-didodecyl-6,7-difluoroquinoxaline as the electron-deficient unit and thienothiophene as the electron rich units were synthesized by Stille coupling. The small molecules exhibit satisfactory thermal stability and a broad absorption band from 400 to 700 nm. The HOMO/LUMO energy levels of SM1, SM2, and SM3 were -5.70/-3.48, -5.57/-3.42, and -5.66/-3.59 eV, respectively. SM3 with the alkyl group at 4-position in terminal thiophene units has lower HOMO energy levels to increase the V-OC value

Synthesis and properties of polyfluorene, containing oxadiazole and carbazole units as pendants for white light-emitting diodes

Polyfluorene-based conjugated polymer, containing oxadiazole and carbazole units as pendants, was prepared as the emitting layer in light-emitting diodes (LEDs) to show that it has higher maximum brightness and electroluminescence (EL) efficiency as compared to poly(9,9-bis(2-ethylhexyl)fluorene-2,7-diyl). The prepared polymer, poly[9-(6-(N-carbazolyl)-hexyl)-9-(6-(4-(5-phenyl-1,3,4-oxadiazolyl)-phenoxy)-hexyl)-fluorene-2,7-diyl] was used as the emitting layer in LEDs. Oxadiazole and carbazole units as pendants caused aggregation to generate broad peak around 547 nm. The Commission internationale de l'eclairage coordinate of the LEDs was (0.28, 0.30) which is quite close to that of the standard white of National Television Systems Committee (0.31, 0.33). The maximum brightness and EL efficiency of the device with aluminum cathode were 6400 cd/m2 at 10V and 0.50 cd/A at 290mA/cm2, respectively.close10

Enhanced open circuit voltage by hydrophilic ionic liquids as buffer layer in conjugated polymer-nanoporous titania hybrid solar cells

We demonstrate the fabrication of a nanoporous titania (NP-TiO(2)) network structure by using a polystylene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymer template and modifying the surface of NP-TiO(2) with ionic liquids (ILs), bmim-BF(4) and benmim-Cl. The effect of the molecular weight of PS-b-P4VP on the morphology of the NP-TiO(2) and IL-modified NP-TiO(2) are characterized by scanning electron microscopy and contact angle measurements. Subsequently, hybrid solar cells are fabricated using MEH-PPV and NP-TiO(2), and the effect of IL layers and IL concentrations on device performances are evaluated under AM 1.5 G illumination. The devices containing bmim-BF(4) and benmim-Cl show drastically enhanced open circuit voltages (V(oc)) of 1.05 V and 0.91 V, respectively, while the reference device without an IL layer exhibits a V(oc) of 0.60 V. Significantly improved V(oc) can be attributed to the change in interfacial energy levels by formation of ionic double layers at the TiO(2)/IL and at the IL/MEH-PPV interfaces. We also observed the trend that short circuit current decreased and V(oc) increased with increasing IL concentration, which is ascribed to interruption of charge transfer from MEH-PPV to TiO(2) and the change in interfacial energy level by shifting the vacuum level, respectively.close121

Thermally Durable Nonfullerene Acceptor with Nonplanar Conjugated Backbone for High-Performance Organic Solar Cells

A nonfullerene acceptor (NFA) with acceptor-donor-acceptor (A-D-A) architecture, i-IEICO-2F, based on 4,9-dihydro-s-indaceno[1,2-b:5,6-b ']dithiophene as an electron-donating core and 2-(6-fluoro-2,3-dihydro-3-oxo-1H-inden-1-ylidene)-propanedinitrile as electron-withdrawing end groups, is designed and synthesized. i-IEICO-2F has a twist structure in the main conjugated chain, which causes blueshifted absorption and leads to harmonious absorption with a high bandgap donor. The bandgap of i-IEICO-2F compliments the bandgap of suitable wide bandgap donor polymers such as J52, leading to complete light absorption throughout the visible spectrum. Devices based on i-IEICO-2F exhibit optimized photovoltaic performance including an open-circuit voltage of 0.93 V, a short-circuit current density of 16.61 mA cm(-2), and a fill factor of 73%, and result in a power conversion efficiency (PCE) of 11.28%. The i-IEICO-2F-based devices reach PCEs of >11% without using any additives or post-treatments. Devices are found to be thermally stable and maintain 44% of their initial PCE after 184.5 h of continuous thermal annealing (TA) treatment at 150 degrees C. Based on UV, atomic force microscopy (AFM), and grazing incidence wide angle X-ray scattering (GIWAXS) results, i-IEICO-2F devices show almost identical morphology and molecular orientation throughout the TA treatment and excellent stability compared to other IEICO derivatives

Low bandgap small molecules based on 2,2-bithiophene-3,3-dicarboximide for soluble-processed solar cells

Small molecules, SM1 and SM2, with bithiophene-imide as the central electron deficient unit and bridged thiophene and terminal triphenyl amine as electron rich units, have been designed and synthesized. The dithienoazepinedione, bithiophene imide (BTI) group, is an attractive electron deficient unit since it demonstrates strong electron-withdrawing character, a planar architecture, and good solubility. The spectra of SM1 and SM2 in the solid thin films show absorption bands with maximum peaks at 368, 495 and 397, 517 nm, and the absorption onsets at 598 and 631 nm. The electrochemical band gaps are about 1.45 and 1.43 eV, somewhat lower than the optical band gaps. The best device with SM1: PC71BM in chloroform with thermal treatment at 130 C showed VOC of 0.91 V, JSC of 3.93 mA/cm2, and FF of 0.38, which yielded PCE of 1.36%.close0

Pyrrolo[3,2-b]pyrrole-Based Copolymers as Donor Materials for Organic Photovoltaics

A new accepter unit, pyrrolo[3,2-b]pyrrole-2,5-dione, was prepared and utilized for the synthesis of the conjugated polymers containing electron donor-acceptor pair for OPVs. Pyrrolo[3,2-b]pyrrole-2,5-dione unit, regioisomer of the known pyrrolo[3,4-c]pyrrole-1,4-dione, is originated from the structure of stable synthetic pigment. The new conjugated polymers with 1,4-diphenylpyrrolo[3,2-b]pyrrole-2,5-dione, thiophene and carbazole were synthesized using Suzuki polymerization to generate P1 and P2. The solid films of P1 and P2 show absorption bands with maximum peaks at about 377, 554 and 374, 542 nm and the absorption onsets at 670 and 674 nm, corresponding to band gaps of 1.85 and 1.84 eV, respectively. To improve the hole mobility of the polymer with 1,4-bis(4-butylphenyl)-pyrrolo[3,2-b]-pyrrole-2,5-dione unit, which was previously reported by us, the butyl group at the 4-positions of the N-substituted phenyl group was substituted with hydrogen and methyl group. The field-effect hole mobility of P2 is 9.6 ?? 10-5 cm2/Vs. The device with P2:PC71BM (1:2) showed VOC value of 0.84 V, JSC value of 5.10 mA/cm2, and FF of 0.33, giving PCE of 1.42%.close0

Synthesis of the pyrrolo[3,2-b]pyrrole-based copolymer with enhanced open circuit voltage

A new accepter unit, pyrrolo[3,2-b]pyrrole-2,5-dione, was prepared and utilized for the synthesis of the conjugated polymer containing electron donor-acceptor pair for OPVs. Pyrrolo[3,2-b]pyrrole-2,5-dione unit, regioisomer of the known pyrrolo[3,4-c]pyrrole-1,4-dione, is originated from the structure of stable synthetic pigment. The new conjugated polymer with pyrrolo[3,2-b]pyrrole-2,5-dione, thiophene and carbazole was synthesized using Suzuki polymerization to generate P1. The solid thin film of P1 shows absorption band with maximum peaks at 374 and 548 nm, and the absorption onset at 679 nm, corresponding to band gap of 1.83 eV. The field-effect hole mobility of P1 is 2.2 x 10(-5) cm(2)/Vs. The device based on the polymer:PCBM (1:2) blend without thermal treatment showed a V-OC of 0.82 V, a J(SC) of 6.28 mA/cm(2), and an FF of 0.39, giving a PCE of 2.00%.close