Highlights of the August 2017 issue of Australian Journal of Chemistry include two reviews, one each from the UK and India, and a research article from Northern Ireland. Daniel Lynch of Exilica Ltd (UK) and Darren Hamilton of the Department of Chemistry, Mount Holyoke College, USA, provide a historical overview of azulenyl squaraines, a class of organic dye that possesses properties that make the dyes highly attractive for optical data storage. These organic molecules are defined as either symmetrical or unsymmetrical squaraine compounds prepared through the 1:2 condensation reaction of 3,4-dihydroxycyclobut-3-ene-l,2-dione (squaric acid) and azulene (or an associated derivative such as an aza-azulene), or condensation of an azulenyl half-squarine with a suitable electron-donating aromatic system such as an N-substituted 2,3,3-trimethylindolenine (see scheme). From the first reported synthesis of an azulenyl squaraine in 1966, these compounds have been intensely investigated because they absorb within the wavelength range of a semiconductor laser beam, i.e. within an approximate range of 700-900 nm. The authors report on the fascinating synthesis chemistry and on potential novel applications such as in biomedicine as photosensitisers in photodynamic therapy.
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