Development of 1-Hydroxy-2(1H)-quinolone-Based Photoacid Generators and Photoresponsive Polymer Surfaces

A new class of carboxylate and sulfonate esters of 1-hydroxy-2(1H)-quinolone has been demonstrated as nonionic photoacid generators (PAGs). Irradiation of carboxylates and sulfonates of 1-hydroxy-2(1H)-quinolone by UV light (λ≥310?nm) resulted in homolysis of weak N?O bond leading to efficient generation of carboxylic and sulfonic acids, respectively. The mechanism for the homolytic N?O bond cleavage was supported by time-dependent DFT calculations. Photoresponsive 1-(p-styrenesulfonyloxy)-2-quinolone-methyl methacrylate (SSQL-MMA) and 1-(p-styrenesulfonyloxy)-2-quinolone-lauryl acrylate (SSQL-LA) copolymers were synthesized from PAG monomer 1-(p-styrenesulfonyloxy)-2-quinolone, and subsequently controlled surface wettability was demonstrated for the above-mentioned photoresponsive polymers.     

Recent Advances and Challenges in the Design of Organic Photoacid and Photobase Generators for Polymerizations

Photopolymerization, or the use of light to trigger polymerization, is one of the most exciting technologies for advanced manufacturing of polymers. One of the key components in the photopolymerization processes is the photoactive compound that absorbs the light, generating the active species that promotes the polymerization and largely determines the final properties of the material. The field of photopolymerization has been dominated by photoradical generators to mediate radical reactions. In the last decade, to expand the number of polymers that can be prepared by photopolymerization, intensive research has been devoted to the synthesis and utilization of photoactive molecules that are able to generate a base or an acid upon irradiation. These organic compounds are known to promote not only the ring‐opening polymerization of various heterocyclic monomers such as lactones, carbonates, or epoxides but also to trigger the step‐growth synthesis of polyurethanes. This Minireview highlights the recent advances in the development of organic photobase and photoacid generators, with the aim of encouraging the wider application of these photoactive compounds in the photopolymerization area and to expand the use of these polymers in advanced manufacturing processes.     

Versatile preparation of poly(1,4‐phenylenevinylene‐co‐1,4‐phenylene‐1,2‐ethanediyl) by CVD polymerization of p‐(methoxymethyl)benzyl chloride

It was demonstrated that a series of copolymers consisting of 1,4‐phenylenevinylene (PV) and 1,4‐phenylene‐1,2‐ethanediyl (PE) units could be prepared from a single monomer, p‐(methoxymethyl)benzyl chloride, via the chemical vapor deposition polymerization (CVDP) method. The composition of the copolymers could be varied simply by altering the monomer activation temperature. The higher the temperature, the lower the content of the PV unit. The photo (PL)‐ and electroluminescence (EL) properties of the copolymers that revealed a blueshift when compared with PPV strongly depend on the amount of the PE units incorporated. The external quantum efficiencies of the electroluminescence devices having the configuration of ITO/PEDOT‐PSS/copolymer/Al‐Li were higher than that of PPV, which can be ascribed to the improved confinement of excitons. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 742–751, 2005     

Novel Anionic Photoacid Generators (PAGs) and Corresponding PAG Bound Polymers

Summary: A new series of functionalized anionic photoacid generators (PAGs), and corresponding polymers were prepared in moderate to good yield and characterized. The thermostability of PAG bound polymers was superior to PAG blend polymers. The fluorine‐free PAG bound or blend polymers exhibited higher stability than fluorine‐substituted PAG bound or blend polymers. Although the acid generating efficiency of PAG blend polymers was higher than that of PAG bound polymers, yet it is anticipated that PAG incorporated into the polymer main chain may improve acid diffusion compared with the PAG blend polymers. This was demonstrated by preliminary electron beam lithography (EBL) results: the fluorine PAG bound polymer resist HE‐F4‐MBS‐TPS gave 35 nm 1:1 L/S and showed better resolution than the blend sample HE Blend F4‐IBBS‐TPS. The PAG bound resist showed the capability for higher resolution, since 30 nm 2:1 L/S patterned. Based on these preliminary EBL results, the PAG bound polymer samples are anticipated to have a resolution capability for the 32 nm node for EUVL.

Design of microstructures for EUV lithography.     

Synthesis and Characterizations of Regioregular Poly(3‐alkylthiophene) with Alter1483ting Dodecyl/1H,1H,2H,2H‐Perfluorooctyl Side Chains

A regioregular poly[4′‐dodecyl‐3‐(1H,1H,2H,2H‐perfluorooctyl)‐2,2′‐bithiophene] (P3DDFT) with alternating alkyl and semifluoroalkyl side chains were synthesized. Short ethylene spacer between perfluorohexyl part and thiophene did not largely affect the absorption and emission properties of the polythiophene backbone in comparison with poly(3‐dodecylthiophene) (P3DDT). P3DDFT showed a larger onset of the oxidation potential (+0.17 V) observed by cyclic voltamogram due to the electron withdrawing effect of the fluoroalkyl part. Thermal analysis and X‐ray diffraction patterns indicated that P3DDFT in the solid state forms a semicrystalline lamellar structure that is similar to that of P3DDT. Ultraviolet photoemission spectroscopy was also used to investigate their electron structure in the films. Comparison of hole mobilities in the films suggested that P3DDFT could have a less ordered packing structure compared to P3DDT both in the bulk and at the dielectric interface.

     

Photochemistry of N‐Arylsulfonimides: An Easily Available Class of Nonionic Photoacid Generators (PAGs)

The photochemical behavior of differently substituted N‐arylsulfonimides was investigated. Homolysis of the S?N bond took place as the exclusive path from the singlet state to afford both N‐arylsulfonamides and photo‐Fries adducts, the amount of which depended on reaction conditions and aromatic substituents. Sulfinic and sulfonic acids were released upon irradiation under deaerated and oxygenated conditions, respectively. The nature of the excited states and intermediates involved were proved by laser flash photolysis and EPR experiments. These results highlighted the potential of such compounds as nonionic photoacid generators able to photorelease up to two equivalents of a strong acid for each mole of substrate.     

Synthesis of Poly(benzothiadiazole‐co‐dithienobenzodithiophenes) and Effect of Thiophene Insertion for High‐Performance Polymer Solar Cells

We describe herein the synthesis of novel donor–acceptor conjugated polymers with dithienobenzodithiophenes (DTBDT) as the electron donor and 2,1,3‐benzothiadiazole as the electron acceptor for high‐performance organic photovoltaics (OPVs). We studied the effects of strategically inserting thiophene into the DTBDT as a substituent on the skeletal structure on the opto‐electronic performances of fabricated devices. From UV/Vis absorption, electrochemical, and field‐effect transistor analyses, we found that the thiophene‐containing DTBDT derivative can substantially increase the orbital overlap area between adjacent conjugated chains and thus dramatically enhance charge‐carrier mobility up to 0.55 cm² V^?1 s^?1. The outstanding charge‐transport characteristics of this polymer allowed the realization of high‐performance organic solar cells with a power conversion efficiency (PCE) of 5.1 %. Detailed studies on the morphological factors that enable the maximum PCE of the polymer solar cells are discussed along with a hole/electron mobility analysis based on the space‐charge‐limited current model.     

Synthesis of dual‐functional copolymer with orthogonally photosensitive groups

A dual‐functional copolymer, poly(4‐styrenesulfonyl azide‐co‐t‐butyl‐methacrylate), with built‐in photoacid labile and photocrosslinkable components was designed and synthesized by radical copolymerization. The mixture of copolymer and photoacid generators was spin coated on aminosilane treated Si wafers and polycarbonate (PC). When exposed to 365 nm UV light, photoacids were generated, which decomposed the acid labile groups, t‐butyl‐ester, to carboxylic acid in the exposed region, leading to drastic change of wettability from hydrophobic to hydrophilic after developing the film in an aqueous base solution. The patterned polymer film could be subsequently photoimmobilized on the substrate under 254 nm deep UV exposure through C? H insertion via exited azide groups. ¹H‐NMR and Fourier transform infrared spectra confirmed the synthesis of the copolymer, and the photodecomposition and photografting reactions occurred orthogonally at 365 and 254 nm, respectively, without interfering each other. On the patterned surfaces, including a hexagonal dot array and a gradient line array, we demonstrated selective wetting in the 365 nm exposed regions. On the gradient line array, we showed an interesting ratchet wetting pattern. Finally, we showed that the copolymer could be used to modify the wettability of PC while maintaining its high optical quality. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Donor–acceptor alternating π‐conjugated polymers containing Di(thiophen‐2‐yl)pyrene and 2,5‐Bis(2‐octyldodecyl)pyrrolo[3,4‐c]pyrrole‐1,4(2H,5H)‐dione for organic thin‐film transistors

New diketopyrrolopyrrole (DPP)‐containing conjugated polymers such as poly(2,5‐bis(2‐octyldodecyl)‐3‐(5‐(pyren‐1‐yl)thiophen‐2‐yl)‐6‐(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,4(2H,5H)‐dione) (P(DTDPP‐alt‐(1,6)PY)) and poly(2,5‐bis(2‐octyldodecyl)‐3‐(5‐(pyren‐2‐yl)thiophen‐2‐yl)‐6‐(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,4(2H,5H)‐dione) (P(DTDPP‐alt‐(2,7)PY)) were successfully synthesized via Suzuki coupling reactions under Pd(0)‐catalyzed conditions. P(DTDPP‐alt‐(2,7)PY), incorporating 2,5‐bis(2‐octyldodecyl)‐3,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,4(2H,5H)‐dione (DTDPP) at the 2,7‐position of a pyrene ring showed a lower band‐gap energy (E. = 1.65 eV) than the 1,6‐substituted analog, P(DTDPP‐alt‐(1,6)PY) (E = 1.71 eV). The energies of the molecular frontier orbitals of the substituted polymers were successfully tuned by changing the anchoring position of DTDPP from the 1,6‐ to the 2,7‐position of the pyrene ring. An organic thin‐film transistor fabricated using the newly synthesized P(DTDPP‐alt‐(2,7)PY), as a semiconductor material exhibited a maximum mobility of up to 0.23 cm² V^?1 s^?1 (I_on/off ～ 10⁶), which was much larger than that obtained using P(DTDPP‐alt‐(1,6)PY). This distinction is attributed to morphological differences in the solid state arising from differences between the geometrical configurations of DTDPP and the pyrene ring. In addition, the organic phototransistor devices made of P(DTDPP‐alt‐(2,7)PY) showed interesting photoinduced enhancement of drain current when irradiating the excitation light whose intensity is very small. Based on the photoinduced effect on I_DS, photocontrolled memory could be realized under the variation of gate voltages. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Three‐Way‐Switchable (Right/Left/OFF) Selective Reflection of Circularly Polarized Light on Solid Thin Films of Helical Polymer Blends

Two poly(quinoxaline‐2,3‐diyl) copolymers bearing miscibility‐enhancing 8‐chlorooctyloxy and (S)‐2‐methylbutoxy or n‐butoxy side chains were synthesized. After annealing in CHCl₃ vapor, a polymer‐blend film of these copolymers exhibited selective reflection of right‐handed circularly polarized light (CPL) in the visible region. The handedness of the CPL reflected was completely inverted upon annealing of the film in THF vapor. Annealing in n‐hexane vapor resulted in the phase separation of the polymer blend, which turned the selective reflection off. This three‐way‐switchable reflection, that is, reflection of right‐handed or left‐handed CPL, together with an OFF state, could be observed visually through right‐ and left‐handed CPL filters.     

Synthesis and photophysical properties of Rhodamine B dye‐bearing poly(isobutyl methacrylate‐co‐2,2,2‐trifluoroethyl methacrylate) as a temperature‐sensing polymer film

To develop a novel temperature‐sensitive paint, methacrylamide monomers bearing Rhodamine B dye (two regioisomers, 3a and 3b ) were synthesized and polymerized with isobutyl methacrylate and 2,2,2‐trifluoroethyl methacrylate to afford Rhodamine B‐pendant polymers 4a and 4b . The methacrylamide monomers 3a and 3b showed photophysical properties almost identical with those of Rhodamine B. The temperature sensitivity of the luminescence intensity of 3a and 3b was also similar to that of Rhodamine B. The polymers 4a and 4b have excellent solubility in nonpolar organic solvents and are suitable for application as paint. Films of polymers 4a and 4b showed temperature‐dependent luminescence, which is applicable for temperature‐sensing. The temperature sensitivity of the film of 4a was estimated to be ?0.37% °C^?1, and was independent of pressure. The film of 4b showed higher temperature sensitivity, but its temperature sensitivity was slightly pressure‐dependent. Hence, polymer 4a is expected to be superior for practical use in paints having temperature‐sensing functionality. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2876–2885, 2007     

Secondary doping in poly(3,4‐ethylenedioxythiophene):Poly(4‐styrenesulfonate) thin films

The electrical and structural properties of poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS) thin films deposited from aqueous dispersion using different concentrations of selected secondary dopants are studied in detail. An improvement of the electrical conductivity by three orders of magnitude is achieved for dimethyl sulfoxide, sorbitol, ethylene glycol, and N,N‐dimethylformamide, and the secondary dopant concentration dependence of the conductivity exhibits almost identical behavior for all investigated secondary dopants. Detailed analysis of the surface morphology and Raman spectra reveals no presence of the secondary dopant in fabricated films, and thus the dopants are truly causing the secondary doping effect. Although the ratio of benzenoid and quinoid vibrations in Raman spectra is unaffected by doping, the phase transition in PEDOT:PSS films owing to doping is confirmed. Further analysis of temperature‐dependent conductivity reveals 1D variable range hopping (VRH) charge transport for undoped PEDOT:PSS, whereas highly conductive doped PEDOT:PSS films exhibit 3D VRH charge transport. We demonstrate that the charge ‐ hopping dimensionality change should be a fundamental reason for the conductivity enhancement. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1139–1146     

Enhanced Performance of Benzothieno[3,2‐b]thiophene (BTT)‐Based Bottom‐Contact Thin‐Film Transistors

Three new benzothieno[3,2‐b]thiophene ( BTT ; 1 ) derivatives, which were end‐functionalized with phenyl ( BTT‐P ; 2 ), benzothiophenyl ( BTT‐BT ; 3 ), and benzothieno[3,2‐b]thiophenyl groups ( BBTT ; 4 ; dimer of 1 ), were synthesized and characterized in organic thin‐film transistors (OTFTs). A new and improved synthetic method for BTT s was developed, which enabled the efficient realization of new BTT ‐based semiconductors. The crystal structure of BBTT was determined by single‐crystal X‐ray diffraction. Within this family, BBTT , which had the largest conjugation of the BTT derivatives in this study, exhibited the highest p‐channel characteristic, with a carrier mobility as high as 0.22 cm² V^?1 s^?1 and a current on/off ratio of 1×10⁷, as well as good ambient stability for bottom‐contact/bottom‐gate OTFT devices. The device characteristics were correlated with the film morphologies and microstructures of the corresponding compounds.     

A Free‐standing electrochromic material of poly(5,7‐bis(2‐(3,4‐ethylenedioxy)thienyl)‐indole) and its application in electrochromic device

Free‐standing poly(5,7‐bis(2‐(3,4‐ethylenedioxy)thienyl)‐indole) (PETI) was electrochemically obtained from 5,7‐bis(2‐(3,4‐ethylenedioxy)thienyl)‐indole (ETI) prepared by Stille coupling reaction of 5,7‐dibromoindole and 3,4‐ethylenedioxythiophene. For comparison, poly(5,7‐bis(2‐thiophene)‐indole) was also electrosynthesized from 5,7‐bis(2‐thiophene)‐indole (BTI) which was prepared from the 5,7‐dibromoindole and thiophene. Characterizations of ETI and BTI were performed by cyclic voltammetry, scanning electron microscopy, ¹H NMR, and ¹³C NMR spectroscopy. Spectroelectrochemical studies showed PETI had better electrochromic properties and showed two different colors (brown and blue‐violet) under various potentials with better maximum contrast (ΔT%) and coloration efficiency (CE). An electrochromic device (ECD) based on PETI and poly(3,4‐ethylenedioxythiophene) (PEDOT) was also constructed and characterized. This ECD had fast response time, high CE, better optical memory, and long‐term stability. These results indicated that PETI had potential applications for ECD. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2356–2364     

Self‐Aligned Micropatterns of Bifunctional Polymer Surfaces with Independent Chemical and Topographical Contrast

Bifunctional surfaces are micropatterned using a self‐aligned, dual‐purpose lithographic mask and pairs of conformally deposited iCVD polymers. A first layer is deposited, then physically masked and etched in oxygen plasma. A second layer is deposited with the mask still in place. Lift‐off reveals the micropatterned surface. The thicknesses of the two layers are independently controlled so that the resultant surface displays both chemical and topographical contrast. The patterning scheme is independent of the polymers used and order of deposition. We use this scheme to create surfaces that spatially confine microcondensation, as well as chemical functionality. We also demonstrate microwells whose depth can be altered in response to a water stimulus.

     

Enhancing electrochromic properties of conducting polymers via copolymerization: Copolymer of 1‐(4‐fluorophenyl)‐2,5‐di(thiophen‐2‐yl)‐1H‐pyrrole with 3,4‐ethylene dioxythiophene

A copolymer of 1‐(4‐fluorophenyl)‐2,5‐di(thiophen‐2‐yl)‐1H‐pyrrole (FPTP) with 3,4‐ethylene dioxythiophene (EDOT) was electrochemically synthesized and characterized. While poly(FPTP) (P(FPTP)) has only two colors in its oxidized and neutral states (blue and yellow), its copolymer with EDOT has five different colors (purple, red, light gray, green, and blue). Electrochromic devices based on P(FPTP‐co‐EDOT) and poly(3,4‐ethylenedioxythiophene) (PEDOT) were constructed and characterized. The oxidized state of the device shows blue color whereas it shows purple for the reduced state. At several potentials the device has good transparency with green and gray colors. Maximum contrast (Δ%T) and switching time of the device were measured as 23% and 1.1 s at 555 nm. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4496–4503, 2007     

Excited‐State Proton Transfer and Conformational Relaxation of 2‐(4′‐Pyridyl)benzimidazole in Nafion Films

The effect of annealing on the acidity and water uptake of Nafion films has been studied by using the acidity sensing fluorophore 2‐(4′‐pyridyl)benzimidazole (4PBI). The difference in acidity and the microenvironment of the fluorophore in annealed and nonannealed films is brought out in this study. The annealed film is found to have less water uptake than nonannealed films. The amount of water uptake increases upon acid treatment of the films, as all the steady‐state and time‐resolved behaviour of the molecule in nonannealed films is restored. These observations are rationalised by the formation of anhydrides upon annealing and their hydrolysis to sulfonic acid groups upon acid treatment. Interestingly, the acidity of annealed films is found to be even less than that of Na⁺exchanged films, indicating that annealing removes more protons from the Nafion films than cation exchange can.