Synthesis,characterization of naphthalene‐based polyimides,and their use as immobilized enzyme membrane

A new monomer, 1,5‐bis(p‐dimethylaminophenylimino)naphthalene, was prepared through Schiff‐base condensation reaction of 1,5‐diaminonaphthalene and 4‐(dimethylamino)benzaldehyde in the presence of ethanol. A series of aromatic polyimides bearing naphthalene and ? CH?N? groups were synthesized from the diamine with five kinds of commercial dianhydrides via a conventional one‐stage process. The resulting naphthalene based polyimides (NBPs) showed good solubilities in N‐methyl‐2‐pyrrolidone and m‐cresol. NBPs had glass‐transition temperatures at 139–174°C and 10% weightloss temperatures above 430 °C in nitrogen atmospheres. Excellent properties of NBPs are attributed to the incorporation of the naphthalene and ? CH?N? group in 1,5‐bis(p‐dimethylaminophenylimino)naphthalene. Moreover, chemically prepared polyimides were used for immobilization of glucose oxidase (GOx). The amperometric responses of the NBPs‐GOx‐Pt electrodes toward glucose were examined at a potential of 0.7 V in PBS solution by means of time‐base (TB) technique. Results show that NBPs bearing ? O? group membrane (PI‐3) has many advantages in the immobilization of glucose oxidase because of its strong adherence to electrode surface and chemical stability and selectivity. Copyright © 2010 John Wiley & Sons, Ltd.     

Coumarin‐3‐Aldehyde as a Scaffold for the Design of Tunable PET‐Modulated Fluorescent Sensors for Neurotransmitters

NeuroSensor 521 (NS521) is a fluorescent sensor for primary‐amine neurotransmitters based on a platform that consists of an aryl moiety appended to position C4 of the coumarin‐3‐aldehyde scaffold. We demonstrate that sensors based on this platform behave as a directly linked donor–acceptor system that operates through an intramolecular acceptor‐excited photoinduced electron transfer (a‐PET) mechanism. To evaluate the PET process, a series of benzene‐ and thiophene‐substituted derivatives were prepared and the photophysical properties, binding affinities, and fluorescence responses toward glutamate, norepinephrine, and dopamine were determined. The calculated energy of the highest occupied molecular orbital (E_HOMO) of the pendant aryl substituents, along with oxidation and reduction potential values derived from the calculated molecular orbital energy values of the platform components, allowed for calculation of the fluorescence properties of the benzene sensor series. Interestingly, the thiophene derivatives did not fit the typical PET model, highlighting the limitations of the method. A new sensor, NeuroSensor 539, displayed enhanced photophysical properties aptly suited for biological imaging. NeuroSensor 539 was validated by selectively labeling and imaging norepinephrine in secretory vesicles of live chromaffin cells.     

Ultrafast Relaxation Dynamics of the Excited States of 1‐Amino‐ and 1‐(N,N‐Dimethylamino)‐fluoren‐9‐ones

The dynamics of the excited states of 1‐aminofluoren‐9‐one (1AF) and 1‐(N,N‐dimethylamino)‐fluoren‐9‐one (1DMAF) are investigated by using steady‐state absorption and fluorescence as well as subpicosecond time‐resolved absorption spectroscopic techniques. Following photoexcitation of 1AF, which exists in the intramolecular hydrogen‐bonded form in aprotic solvents, the excited‐state intramolecular proton‐transfer reaction is the only relaxation process observed in the excited singlet (S₁) state. However, in protic solvents, the intramolecular hydrogen bond is disrupted in the excited state and an intermolecular hydrogen bond is formed with the solvent leading to reorganization of the hydrogen‐bond network structure of the solvent. The latter takes place in the timescale of the process of solvation dynamics. In the case of 1DMAF, the main relaxation pathway for the locally excited singlet, S₁(LE), or S₁(ICT) state is the configurational relaxation, via nearly barrierless twisting of the dimethylamino group to form the twisted intramolecular charge‐transfer, S₁(TICT), state. A crossing between the excited‐state and ground‐state potential energy curves is responsible for the fast, radiationless deactivation and nonemissive character of the S₁(TICT) state in polar solvents, both aprotic and protic. However, in viscous but strong hydrogen‐bond‐donating solvents, such as ethylene glycol and glycerol, crossing between the potential energy surfaces for the ground electronic state and the hydrogen‐bonded complex formed between the S₁(TICT) state and the solvent is possibly avoided and the hydrogen‐bonded complex is weakly emissive.     

Donor‐Acceptor‐Functionalized Tetraethynylethenes with Nitrothienyl Substituents: Structure‐Property Relationships

Tetraethynylethenes (TEEs) functionalized with donor (4‐(dimethylamino)phenyl) and acceptor (5‐nitro‐2‐thienyl) groups were prepared by Pd⁰‐catalyzed Sonogashira cross‐coupling reactions (Schemes 1 – 6). The physical properties of these novel chromophores were examined and compared with those of analogous systems containing 4‐nitrophenyl instead of 5‐nitro‐2‐thienyl acceptor groups. X‐Ray crystal‐structure analyses showed the π‐conjugated frameworks of 2 , 11 , and 13 , including the TEE core and all aryl moieties, to be nearly perfectly planar (Figs. 1, 3, and 4). In contrast, one 4‐(dimethylamino)phenyl group in 10 is rotated almost 90° out of the molecular plane, presumably due to crystal‐packing effects (Fig. 2). The analysis of bond lengths and bond angles revealed little, if any, evidence of intramolecular ground‐state donor‐acceptor interactions. The electrochemical behavior of nitrothienyl‐substituted TEEs is similar to that of the corresponding nitrophenyl‐functionalized derivatives (Table 3). The nitrothienyl groups were reduced at −1.23 V (vs. the ferrocene/ferricinium couple, Fc/Fc⁺), regardless of the degree or pattern of other substitutions. For nonsymmetrical TEE 13 , the reduction of the nitrothienyl group at −1.23 V is followed by a reduction of the nitrophenyl group at −1.40 V, a potential typical for the reduction of other nitrophenyl‐substituted TEEs, such as 17 – 20 . UV/VIS Spectroscopy showed a consistently lower‐energy absorption cutoff for nitrothienyl derivatives compared with the analogous nitrophenyl‐substituted TEEs that confirms a lowering of the HOMO‐LUMO gap as a result of nitrothiophene substitution (Figs. 5 and 6). A comparison of the tetrakis‐arylated TEEs 11 , 13 , and 20 clearly showed a steady bathochromic shift of the longest‐wavelength absorption maximum and the end‐absorption upon sequential replacement of nitrophenyl by nitrothienyl groups. Quantum‐chemical computations were performed to explain a number of complex features of the electronic absorption spectra. All empirical features of relevance in the experimental UV/VIS spectra for 2 , 5 , 6 , and 17 – 19 were correctly reproduced by computation (Tables 4 and 5). The combination of theory and experiment was found to be very useful to explain the particular acceptor properties of the 5‐nitro‐2‐thienyl group.     

Synthesis and properties of novel sulfonated polyimides containing 1,5‐naphthylene moieties

A series of novel sulfonated polyimides (equivalent weight per sulfonic acid = 310–744 g/equiv) containing 10–70 mol % 1,5‐naphthylene moieties were synthesized as potential electrolyte materials for high‐temperature polymer electrolyte fuel cells. The polycondensation of 1,4,5,8‐naphthalene tetracarboxylic dianhydride, 4,4′‐diamino‐2,2′‐biphenyldisulfonic acid, and 1,5‐diaminonaphthalene gave the title polymer electrolytes. The polyimide electrolytes were high‐molecular‐weight (number‐average molecular weight = 36.0–350.7 × 10³ and weight‐average molecular weight = 70.4–598.5 × 10³) and formed flexible and tough films. The thermal properties (decomposition temperature > 260 °C, no glass‐transition temperature), stability to oxidation, and water absorption were analyzed and compared with those of perfluorosulfonic acid polymers. The polyimide containing 20 mol % 1,5‐naphthylene moieties showed higher proton conductivity (0.3 S cm^?1) at 120 °C and 100% relative humidity than perfluorosulfonic acid polymers. The temperature and humidity dependence of the proton conductivity was examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3901–3907, 2003     

Efficient Singlet‐State Deactivation of Cyano‐Substituted Indolines in Protic Solvents via CN?HO Hydrogen Bonds

The photophysical properties of indoline (I) and three of its derivatives, namely, N‐methylindoline (MI), 5‐cyanoindoline (CI), and 5‐cyano‐N‐methylindoline (CMI), are studied in H‐donating solvents of varying polarity. Based on measurements of fluorescence yield and lifetime, and of triplet yield and hydrated‐electron formation, two distinct mechanisms of solvent‐induced fluorescence quenching are evidenced. The first mechanism involves the cyano substituent and leads to an increase in the rate constant of internal conversion of one order of magnitude in ethanolic solution and of more than two orders of magnitude in water, as compared to solutions in n‐hexane or acetonitrile. A similar trend had previously been observed in the case of 4‐N,N‐dimethylaminobenzonitrile (DMABN). The second mechanism reduces the fluorescence lifetimes of the non‐cyanated derivatives in aqueous solution by one order of magnitude and is related to the formation of hydrated electrons. Neither of these mechanisms is influenced by methylation at the ring nitrogen. Quantum chemical calculations are performed on the ground and excited states of the hydrogen‐bonded complexes between protic solvents and MI as well as CMI. Stable hydrogen‐bonded configurations involving the CN substituent and a solvent OH group are found; these configurations are stable both in the ground and the first excited singlet states, whereas the corresponding complex at the ring amino nitrogen is stable in the ground state only. The CN? HO configuration is therefore a prime candidate for a mechanistic explanation of the observed quenching by the first mechanism. These findings may have useful applications for the design of fluorescence probes for water in biological systems.     

Formation of One‐Dimensional Helical Columns and Excimerlike Excited States by Racemic Quinoxaline‐Fused [7]Carbohelicenes in the Crystal

A series of quinoxaline‐fused [7]carbohelicenes (HeQu derivatives) was designed and synthesized to evaluate their structural and photophysical properties in the crystal state. The quinoxaline units were expected to enhance the light‐emitting properties and to control the packing structures in the crystal. The electrochemical and spectroscopic properties and excited‐state dynamics of these compounds were investigated in detail. The first oxidation potentials of HeQu derivatives are approximately the same as that of unsubstituted reference [7]carbohelicene (Heli), whereas their first reduction potentials are shifted to the positive by about 0.7 V. The steady‐state absorption, fluorescence, and circular dichroism spectra also became redshifted compared to those of Heli. The molecular orbitals and energy levels of the HOMO and LUMO states, calculated by DFT methods, support these trends. Moreover, the absolute fluorescence quantum yields of HeQu derivatives are about four times larger than that of Heli. The structural properties of the aggregated states were analyzed by single‐crystal analysis. Introduction of appropriate substituents (i.e., 4‐methoxyphenyl) in the HeQu unit enabled the construction of one‐dimensional helical columns of racemic HeQu derivatives in the crystal state. Helix formation is based on intracolumn π‐stacking between two neighboring [7]carbohelicenes and intercolumn CH ??? N interaction between a nitrogen atom of a quinoxaline unit and a hydrogen atom of a helicene unit. The time‐resolved fluorescence spectra of single crystals clearly showed an excimerlike delocalized excited state owing to the short distance between neighboring [7]carbohelicene units.     

Solvent‐Free One‐Step Photochemical Hydroxylation of Benzene Derivatives by the Singlet Excited State of 2,3‐Dichloro‐5,6‐dicyano‐p‐benzoquinone Acting as a Super Oxidant

Photoinduced hydroxylation of neat deaerated benzene to phenol occurred under visible‐light irradiation of 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ), which acts as a super photooxidant in the presence of water. Photocatalytic solvent‐free hydroxylation of benzene derivatives with electron‐withdrawing substituents such as benzonitrile, nitrobenzene, and trifluoromethylbenzene used as neat solvents has been achieved for the first time by using DDQ as a super photooxidant to yield the corresponding phenol derivatives and 2,3‐dichloro‐5,6‐dicyanohydroquinone (DDQH₂) in the presence of water under deaerated conditions. In the presence of dioxygen and tert‐butyl nitrite, the photocatalytic hydroxylation of neat benzene occurred with DDQ as a photocatalyst to produce phenol. The photocatalytic reactions are initiated by oxidation of benzene derivatives with the singlet and triplet excited states of DDQ to form the corresponding radical cations, which associate with benzene derivatives to produce the dimer radical cations, which were detected by the femto‐ and nanosecond laser flash photolysis measurements to clarify the photocatalytic reaction mechanisms. Radical cations of benzene derivatives react with water to yield the OH‐adduct radicals. On the other hand, DDQ ^{. ?} produced by the photoinduced electron transfer from benzene derivatives reacts with the OH‐adduct radicals to yield the corresponding phenol derivatives and DDQH₂. DDQ is recovered by the reaction of DDQH₂ with tert‐butyl nitrite when DDQ acts as a photocatalyst for the hydroxylation of benzene derivatives by dioxygen.     

m‐Methoxy Substituents in a Tetraphenylethylene‐Based Hole‐Transport Material for Efficient Perovskite Solar Cells

Three tetrapheynlethylene derivatives (N,N‐di(4‐methoxyphenyl)aminophenyl‐substituted tetraphenylethylene; TPE‐4DPA) with different methoxy positions (pp‐, pm‐, and po‐) have been synthesized and characterized. The methoxy groups can control the oxidation potential of the materials, and the electronic properties of the derivatives were affected by the position of the methoxy substituents. These compounds were synthesized in a facile and cost‐effective way, and were applied as hole‐transport materials in perovskite solar cells. The corresponding cell performances were compared with respect to their structure modifications, and it was found that the derivative with m‐OMe substituents showed the highest power conversion efficiency (PCE) of 15.4 %, with a J_sc value of 20.04 mA cm^?2, a V_oc value of 1.07 V, and a fill factor (FF) value of 0.72, which is higher than the p‐OMe and o‐OMe substituents. Moreover, the PCE of pm‐TPE‐4DPA is comparable with that of the state‐of‐the‐art 2,2′,7,7′‐tetrakis(N,N′‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene under identical conditions.     

Benzo[b]phosphole‐Containing π‐Electron Systems: Synthesis Based on an Intramolecular trans‐Halophosphanylation and Some Insights into Their Properties

The intramolecular trans‐halophosphanylation of 2‐(aminophosphanyl)phenylacetylenes mediated by PBr₃ followed by the oxidation with H₂O₂, produces 3‐bromobenzo[b]phosphole oxide derivatives. This cyclization is also used for the synthesis of a 3‐iodo derivative by conducting the reaction in the presence of LiI. Based on this synthetic method, various benzophosphole‐containing π‐conjugated compounds, including a phosphoryl and methylene‐bridged stilbene 10 , 2,3,6,7‐tetraphenylbenzo[1,2‐b:4,5‐b′]diphosphole‐P,P′‐dioxides 11 , and their phosphine sulfide derivatives 12 , are synthesized. The study of the structure–property relationships in a series of the bridged stilbenes, including a bis(methylene)‐bridged stilbene 10 , and a bis(phosphoryl)‐bridged stilbene, reveals that as the contribution of the phosphoryl groups increased, the absorption and emission maxima substantially shift to longer wavelengths. The intrinsic substituent effects of the phosphoryl group in this skeleton are to decrease the oscillator strength of the electronic transition and thus decrease the radiative decay rate constants from the singlet excited state. Nevertheless, these compounds maintain high fluorescence quantum yields (Φ_F>0.8) owing to the significantly retarded nonradiative decay process. In the study of the benzodiphosphole derivatives 11 and 12 , their cyclic voltammetry revealed that both of the phosphoryl and phosphine sulfide derivatives have low reduction potentials (?1.7 to ?1.8 V vs ferrocene/ferrocenium couple) with the high reversibility of the redox waves. These compounds also showed high thermal stabilities with the high glass transition temperatures of 147–159 °C, indicative of their potential utilities as amorphous materials.     

Asymmetrical Fluorene[2,3‐b]benzo[d]thiophene Derivatives: Synthesis,Solid‐State Structures,and Application in Solution‐Processable Organic Light‐Emitting Diodes

A series of novel asymmetrical fused compounds containing the backbone of fluorene[2,3‐b]benzo[d]thiophene (FBT) were effectively synthesized and fully characterized. Single‐crystal X‐ray studies demonstrated that the length of the substituent side chains greatly affects the solid‐state packing of the obtained fused compounds. DFT, photophysical, and electrochemical studies all showed that the FBTs have large band gaps, low‐lying HOMO energy levels, and therefore good stability toward oxidation. Moreover, the substituents strongly influence the fluorescence properties of the resulting FBT derivatives. The di‐n‐hexyl compound exhibits intense fluorescence in solution with the highest quantum yield of up to 91 %. Solution‐processed green phosphorescent organic light‐emitting diodes with the di‐n‐butyl derivative as the host material exhibited a maximum brightness of 14 185 cd m^?2 and a luminescence efficiency of 12 cd A^?1.     

para‐Quinodimethane‐Bridged Perylene Dimers and Pericondensed Quaterrylenes: The Effect of the Fusion Mode on the Ground States and Physical Properties

Polycyclic hydrocarbon compounds with a singlet biradical ground state show unique physical properties and promising material applications; therefore, it is important to understand the fundamental structure/biradical character/physical properties relationships. In this study, para‐quinodimethane (p‐QDM)‐bridged quinoidal perylene dimers 4 and 5 with different fusion modes and their corresponding aromatic counterparts, the pericondensed quaterrylenes 6 and 7 , were synthesized. Their ground‐state electronic structures and physical properties were studied by using various experiments assisted with DFT calculations. The proaromatic p‐QDM‐bridged perylene monoimide dimer 4 has a singlet biradical ground state with a small singlet/triplet energy gap (?2.97 kcal mol^?1), whereas the antiaromatic s‐indacene‐bridged N‐annulated perylene dimer 5 exists as a closed‐shell quinoid with an obvious intramolecular charge‐transfer character. Both of these dimers showed shorter singlet excited‐state lifetimes, larger two‐photon‐absorption cross sections, and smaller energy gaps than the corresponding aromatic quaterrylene derivatives 6 and 7 , respectively. Our studies revealed how the fusion mode and aromaticity affect the ground state and, consequently, the photophysical properties and electronic properties of a series of extended polycyclic hydrocarbon compounds.     

A Spectroscopic and Theoretical Investigation of a Free‐Base meso‐Trithienylcorrole

The unique optical properties of free‐base meso‐tris(5‐methylthien‐2‐yl)corrole were compared to those of the widely investigated meso‐triphenyl‐substituted analogue. A combination of spectroscopic and computational experiments was undertaken to elucidate the relationship between structural features of the neutral, mono‐anionic and mono‐cationic forms of the corroles and their corresponding optical properties. A general bathochromic shift was measured for the thienyl‐substituted corrole. The experimental spectra are supported by excited state calculations. A systematic series of ground state minimizations were performed to determine energy minima for the flexible and solvent‐sensitive molecules. Trithienylcorrole was found to have a more nonplanar macrocycle in conjunction with a high degree of π‐overlap with the meso‐substituents. Both structural features contribute to their bathochromically shifted optical spectra. The configurational character of the thienyl‐substituted corrole is shown to have a larger degree of molecular orbital mixing and doubly excited character, which suggest a more complex electronic structure that does not fully adhere to the Gouterman four‐orbital model. The reactivity of the thienyl groups, particularly with respect to their ability to be (electro)‐polymerized, combined with the tight coupling of the meso‐thienyl groups with the corrole chromophore elucidated in this work, recommends the meso‐thienylcorroles as building blocks in, for instance, organic semiconductor devices.     

Magnetism‐Tunable Oligoacene Dioxide Diradicals: Promising Magnetic Oligoacene‐Like Molecules

Graphene oxide has attracted intense research interest recently because the graphene oxide synthesis route, as a promising alternative for cost‐effective mass production of graphene, has been explored. To further study the oxidation process and possible mechanism and to explore applicability of the oxidized products, we have performed a computational study on three series of oligoacene dioxides, focusing on their structures and electronic properties. Taking 1,5‐dioxidized naphthalene as a starting point, three series of oligoacene dioxides are considered as follows: 1) middle insertion by 1–2 benzene rings; 2) single‐side expansion using 1–2 benzene rings; 3) double‐side expansion using two benzene rings. On the basis of density functional theory and complete active space self‐consistent field (CASSCF) calculations, we reveal that oligoacene dioxides in the middle insertion series have a triplet ground state, whereas those in the single‐side expansion series and the double‐side expansion series have open‐shell broken‐symmetry singlet diradical ground states except for their common origin naphthalene‐1,5‐dioxide whose ground state is triplet and which is also viewed as the origin of the middle insertion series. Magnetic coupling interactions of these oligoacene dioxides are also determined. This work should help people toward an atomistic understanding of the electronic structures and properties of possible intermediates or products and even the oxidation mechanism of graphene sheets, and provides a reasonable strategy of designing novel graphene‐oxide‐based magnetic materials.     

An Unexpected Double Diels–Alder Reaction of (E)‐2‐Bromo‐4‐aryl‐1,3‐pentadiene Involving [1,5]‐Hydrogen Migration and HBr Elimination: Synthesis of Bicyclo[2.2.2]octene Derivatives

An unexpected double Diels–Alder (DDA) reaction of (E)‐2‐bromo‐4‐aryl‐1,3‐pentadiene was developed and resulted in a series of “butterfly‐like” bicyclo[2.2.2]octene derivatives in moderate to good yields without the need for a metal catalyst. The proposed mechanism involves a [1,5]‐sigmatropic hydrogen migration and HBr elimination. Through this decisive [1,5]‐hydrogen shift step, the electronic properties and steric hindrance of the conjugated diene substrate are completely altered and the DDA reaction of this potential diene synthon is successfully achieved.     

Triarylboranes with a 2‐Dimesitylboryl‐2’‐(N,N‐dimethylamino)biphenyl Core Unit: Structure–Property Correlations and Sensing Abilities to Discriminate Between F− and CN− Ions

A series of triarylboranes, in which different substituents are introduced at the para position of the dimethylamino group of a 2‐dimesitylboryl‐2’‐(N,N‐dimethylamino)biphenyl core unit, have been comprehensively investigated to explore the effect of structural modification on photophysical properties. The introduction of electron‐accepting substituents would facilitate the HOMO→LUMO charge transfer (CT) transition. In contrast, the intramolecular CT transition is significantly prohibited when electron‐donating substituents are incorporated. Notably, the HOMO→LUMO CT transition mainly consists of the transition from the electron‐donating amino group to an electron acceptor other than boryl when a strong electron acceptor such as the dicyanovinyl group is present. This dicyanovinyl‐substituted compound displays sensing abilities to discriminate fluoride and cyanide ions. In solution in THF, the fluoride ions first bind to the boron center, then attack the α‐carbon atom of the dicyanovinyl group, whereas the cyanide anion acts on the electron‐accepting centers in the reverse sequence. As a result, the absorption and emission change in different manners upon addition of fluoride and cyanide ions.     

Thermodynamics and Conformations in the Formation of Excited States and Their Interconversions for Twisted Donor‐Substituted Tridurylboranes

We synthesized a series of donor‐substituted tridurylboranes containing different types and number of chromophores including 1‐pyrene (PB1–3), 3‐carbazole (CBC1–3), or substituted p‐carbazol‐N‐phenyl (CBN3a–c) as various donor–acceptor (D–A) molecules. The photophysical and electrochemical properties of these twisted D–A molecules were investigated by means of UV/Vis absorption and fluorescence spectroscopy as well as cyclic voltammetry (CV). Solvent polarity, viscosity, and temperature effects on the fluorescence emission reveal the existence of three types of excited states, and their equilibria and interconversions between three excited states. In increasing order of the charge‐separated extent and the conformational change, three excited states are the locally excited (LE) state, the more planar intramolecular charge‐transfer (ICT) state, and the more twisted ICT (TICT) state as compared to the ground state. The TICT state undergoes a conformational change with a higher energy barrier over the ICT state. The solvent polarity effect on the state conversion is opposite to the viscosity effect, and temperature effects derive from its resulting changes of polarity and viscosity. For example, the increase of the polarity of the solvent results in excited‐state conversions from the LE state to the ICT state, and/or from the ICT to the TICT state, and an increased viscosity leads to the opposite conversions. On the basis of electrochemical and spectral data, thermodynamics of a possible ICT process were estimated, and correlated with the excited‐state character. Finally, three excited states have been characterized by the conformation, the photophysical properties, and the thermodynamics of the ICT processes.     

Regeneration of polycondensation of wholly aromatic poly(azomethine)s with 1,5‐ or 2,6‐substituted naphthalene moiety in main chain

Wholly aromatic poly(azomethine)s with 1,5‐ or 2,6‐substituted naphthalene moiety in the main chains were prepared in aprotic polar solvents or m‐cresol under various reaction conditions. In the polymerization of 1,5‐diaminonaphthalene with terephthalaldehyde, the polymer that synthesized in (HMPA/DMSO) at room temperature for 24 h by adding 5 wt % of calcium chloride and a very small amount of p‐toluenesulfonic acid showed the highest reduced viscosity in all of the polymers from 1,5‐diaminonaphthalene. The reduced viscosity of poly(azomethine)s synthesized from 2,6‐diaminonaphthalene with 2,6‐diformylnaphthalene in m‐cresol and with terephthalaldehyde in HMPA/DMSO were η_red = 0.35 and 0.36, respectively. The thermal analysis showed the poly(azomethine)s had high thermal stability and the glass‐transition temperatures of these polymers are about 250 °C. The X‐ray diffraction showed that they are partially crystalline. They could be polymerized again by second stage polycondensation in polyphosphoric acid. The reduced viscosities of the obtained polymers were about 2–5 times as high as that of the pristine polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1064–1072, 2000     

Systematic Control of the Excited‐State Dynamics and Carrier‐Transport Properties of Functionalized Benzo[ghi]perylene and Coronene Derivatives

A series of benzo[ghi]perylene (Bp) and coronene (Cor) derivatives substituted with electron‐withdrawing methoxycarbonyl (COOMe) or electron‐donating methoxyl (MeO) groups was synthesized. The electrochemical, spectroscopic, and photophysical properties of these compounds were investigated by cyclic voltammetry, steady‐state and time‐resolved spectroscopy, and quantum‐yield measurements. Introduction of suitable substituents onto the aromatic rings enabled control of electrochemical and spectroscopic behavior. Examination of excited‐state dynamics revealed that fluorescence quantum yields increased with increasing number of COOMe groups in both Bp and Cor derivatives, consistent with the findings of DFT calculations. Single‐crystal analysis allowed the performance of field‐effect transistors containing single crystals of the derivatives to be rationalized.     

Synthesis of Soluble Quinacridone Photocatalysts for the Homogeneous Oxidation of Thioethers

Evaluation of quinacridone (QA) derivatives as homogeneous metal-free photocatalysts is here presented. QA derivatives were synthetized and systematically characterized, measuring their ground state and excited state redox potentials in dichloromethane (DCM) and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), in order to understand how structural modifications influenced their photocatalytic properties. In particular, the effect of dicyanomethylene and nitro EWG groups was investigated, in order to develop a photocatalyst capable of promoting oxidative processes in the presence of molecular oxygen. Among the analyzed derivatives, 2,9-dinitro-N,N′-dibutylquinacridone (DNDBQA) was the one with the highest excited state reduction potential (E_red*=1.60 V in HFIP vs SCE), while N,N’-dibutylquinacridone (DBQA) showed valuable excited state redox potentials (E_red*=1.29 V; E_ox*=−1.28 V in HFIP vs SCE), making it suitable for bimodal applications in oxidative and reductive photocatalytic processes. Afterwards, the synthetized QA derivatives were examined as photocatalysts to promote the selective aerobic oxidation of thioether to sulfoxide. Promising results in thioanisole oxidation were achieved with all the QA derivatives tested as photocatalysts, in terms of yield and selectivity. Remarkably, DBQA showed the best performances, catalyzing the reaction in only 20 minutes, using 0.5 % of the photocatalyst, and showing excellent performances in the oxidation of several thioether derivatives.