Australian Journal of Chemistry Australian Journal of Chemistry Society
An international journal for chemical science
Australian Journal of Chemistry

Australian Journal of Chemistry

Volume 68 Number 11 2015

International Year of Light 2015

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Titanium dioxide is a versatile inexpensive heterogeneous photocatalyst. Apart from many applications in environmental chemistry, numerous applications in organic synthesis have been reported. Selective oxidation and reduction of organic compounds and C–C bond formation reactions have been carried out.

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2-Aryl-1,3-dimethylbenzimidazolines (DMBIHs) act as effective electron and hydrogen donors for photoinduced electron-transfer reduction of various organic substrates in which photoexcitation of the substrates as well as photosensitization utilizing substituted pyrenes or transition metal complexes as sensitizers are carried out.

CH15396Visible Light-Promoted Metal-Free Reduction of Organohalides by 2-Naphthyl or 2-Hydroxynaphthyl-Substituted 1,3-Dimethylbenzimidazolines

Eietsu Hasegawa, Kazuma Mori, Shiori Tsuji, Kazuki Nemoto, Taku Ohta and Hajime Iwamoto
pp. 1648-1652
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Visible light excitation of 2-naphthyl- or 2-hydroxynaphthyl-substituted 1,3-dimethylbenzimidazolines (DMBIH) promoted the reduction reaction of some organohalides, involving the cleavage of aromatic as well as aliphatic carbon–halogen bonds. Addition of certain bases, such as 1,8-diazabicyclo[5.4.0]undec-7-ene, significantly enhanced the reducing ability of hydroxynaphthyl-substituted DMBIH.

CH15342A Facile Preparation of α-Aryl Carboxylic Acid via One-Flow Arndt–Eistert Synthesis

Shinichiro Fuse, Yuma Otake, Yuto Mifune and Hiroshi Tanaka
pp. 1657-1661
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An efficient, one-flow Arndt–Eistert synthesis was demonstrated. A sequence of acid chloride formation–nucleophilic acyl substitution–Wolff rearrangement–nucleophilic addition was performed in a microflow system without isolating any intermediates, which included a potentially explosive compound. The microflow system was made from simple, inexpensive, and readily available instruments and tubes.

CH15356Photodecarboxylative Benzylations of N-Methoxyphthalimide under Batch and Continuous-Flow Conditions

Hossein Mohammadkhani Pordanjani, Christian Faderl, Jun Wang, Cherie A. Motti, Peter C. Junk and Michael Oelgemöller
pp. 1662-1667
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Photodecarboxylative benzylations of N-methoxyphthalimide were successfully realized and gave the corresponding benzylated hydroxyphthalimidines in moderate to good yields of 52–73 %. The photobenzylation was furthermore investigated in an advanced continuous-flow photoreactor, which enabled rapid optimization of the reaction conditions and achieved good yields after short residence times.

CH15115Formation of Carbanions from Carboxylate Ions Bearing Electron-Withdrawing Groups via Photoinduced Decarboxylation: Addition of Generated Carbanions to Benzaldehyde

Yuta Kumagai, Takashi Naoe, Keisuke Nishikawa, Kazuyuki Osaka, Toshio Morita and Yasuharu Yoshimi
pp. 1668-1671
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The photoinduced decarboxylation of carboxylate ions bearing electron-withdrawing groups using biphenyl and 1,4-dicyanonaphthalene leads to the efficient generation of carbanions under mild conditions. In particular, the cyanomethyl anion formed using this photochemical method can be added to benzaldehydes to give the corresponding adducts.

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Unprecedented molecular architectures are accessed via intramolecular cycloadditions of photogenerated azaxylylenes. The approach is well-aligned with diversity-oriented synthesis, whereby photoprecursors are synthesised in a modular fashion allowing for up to four diversity inputs, with the complexity of the primary photoproducts being further enhanced using high-yielding post-photochemical steps.

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The photochemical rearrangement of spirooxindole epoxides was performed catalytically with a chiral bifunctional xanthone. The substrates are non-covalently bound via hydrogen bonds to the photochemically active catalyst, which presumably acts as a triplet sensitizer. Upon irradiation with λ 366 nm, the 3-acylindolin-2-ones were formed in high yields (85–98 %) and with enantioselectivities up to 33 % ee.

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The effect of solvent polarity and temperature, as well as excitation wavelength, was examined for the diastereoselectivities of the Paternó-Büchi reaction of chiral cyanobenzoate with 1-(1-naphthyl)-1-phenylethene to reveal the different nature of the excited charge-transfer complex (ECT) and the conventional exciplex (EX). The exciplex ensemble was critically modulated by increased donor–acceptor interactions.

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The rate constant of intersystem crossing (ISC), kISC ~3 × 107 s–1, for cyclopentane-1,3-diyl diradicals was unequivocally determined by the simultaneous observation of the decay process of the triplet diradical (λobs = 320 nm) and the growth process of the corresponding singlet diradical (λobs = 560 nm). The two spin states were directly observed using a long-lived singlet 2,2-dimethoxy-1,3-diphenylcyclopentane-1,3-diyl diradical.

CH15401Formation and Direct Detection of Non-Conjugated Triplet 1,2-Biradical from β,γ-Vinylarylketone

H. Dushanee M. Sriyarathne, Kosala R. S. Thenna-Hewa, Tianeka Scott and Anna D. Gudmundsdottir
pp. 1707-1714
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Intramolecular triplet sensitization of a simple alkene results in the formation of 1,2-biradical. Laser flash photolysis was used to detect the biradical directly; the biradical has a lifetime of a few microseconds. Density functional theory calculations reveal that two radical centres are localized on the adjacent carbon atoms.

CH15412Engineering Disorder at a Nanoscale: A Combined TEM and XAS Investigation of Amorphous versus Nanocrystalline Sodium Birnessite

Rosalie K. Hocking, Hannah J. King, Aimee Hesson, Shannon A. Bonke, Bernt Johannessen, Monika Fekete, Leone Spiccia and Shery L. Y. Chang
pp. 1715-1722
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By coprecipitating a sodium birnessite-like phase with and without phosphate (1.5 %), we are able to engineer two very similar but distinct materials – one that is nanocrystalline and the other that is amorphous.

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The new red-emitting phosphor, La2Zr3(MoO4)9:Eu3+, exhibits broad absorption bands due to admixed Zr4+, Mo6+, and Eu3+ charge transfer (CT) bands. The influence of the various means of excitation on the emission is investigated. A bi-sigmoidal temperature-quenching behaviour was observed and discussed in relation to the CT bands.

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Vertical and lateral carrier mobilities of a polymer donor–PC61BM system were measured with the space charge limited current (SCLC) and field-effect transistor methods. Some blend films annealed at high temperatures exhibited an abrupt increase in the field-effect hole mobility, which was interpreted by an antiplasticization effect.

CH15381Aryl-Substituted Boron Subphthalocyanines and their Application in Organic Photovoltaics

Catherine Bonnier, David S. Josey and Timothy P. Bender
pp. 1750-1758
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Boron subphthalocyanines (BsubPcs) have shown potential as functional materials within organic photovoltaics. In this paper, we revisit an understudied class of BsubPcs with an aryl axial substituent. We have described their relevant properties for application in organic photovoltaics, and incorporated them directly into photovoltaic cells. The resulting cells demonstrate the high potential of this class of BsubPcs within this area.

CH15241Tuning the Light Absorption of Donor–Acceptor Conjugated Polymers: Effects of Side Chains and ‘Spacer' Units in Thieno[3,4-b]pyrazine-Fluorene Copolymers

Michael E. Mulholland, Kristine L. Konkol, Trent E. Anderson, Ryan L. Schwiderski and Seth C. Rasmussen
pp. 1759-1766
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Donor–acceptor (D-A) copolymers of thieno[3,4-b]pyrazine (TP) and fluorene are reported in order to illustrate the ability to tune the light absorption properties of TP-based materials via basic structure–function relationships.

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Materials for organic polymer solar cells should have maximized light absorption across the solar spectrum. An approach is described to synthesize donor–acceptor conjugated polymers that are optimized for light harvesting properties. The best candidate polymer is characterized using a range of photophysical techniques and its performance in solar cell devices evaluated.

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Tin oxide (SnO2) has been widely explored as electron-transport material in solar cells owing to its excellent mobility and transparency. This work reports on the application of SnO2 and SnO2/Sn nanoparticles in perovskite solar cells (PSCs). The study demonstrates a new approach to improve the performance of PSCs through material engineering.

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