The research on selective chromo-fluorogenic sensors for anions, cations and neutral molecules is an exciting topic with recent developments, especially in the possibility of using colorimetric/fluorimetric probes to sense both anions and cations in aqueous solution. In particular, heterocyclic systems which have the ability to act as the recognition unit as well as the signalling unit, are very interesting since variation of their absorption/fluorescence properties can happen during the recognition event. With careful design, for example by inclusion of additional heterocycles, the analyte recognition and overall photophysical properties can be improved, leading to higher sensitivity and selectivity.¹ Imidazole based chromophores have received increasing attention recently due to their distinctive optical properties and excellent thermal stabilities making them versatile systems for several applications such as optical chemosensors and two-photon absorbing molecules,² among other applications in materials and medicinal chemistry. For the recognition of certain anions, anthraquinone derivatives have been reported as suitable systems for colorimetric sensing since they are an example of electron acceptor groups that can be electronically connected with recognition units.³

Based on the above facts, herein we report the synthesis of one imidazo-anthraquinone, and its photophysical and chemosensory properties. The new derivative was obtained in good yield through a Radziszewski reaction between 1,2-diamino anthraquinone and an heterocyclic aldehyde, characterized by the usual techniques and a detailed photophysical study was undertaken. The evaluation of the compound as a colorimetric chemosensor was carried out by performing spectrophotometric titrations in ACN and ACN/H₂O in the presence of relevant organic and inorganic anions, and of alkaline, alkaline-earth and transition metal cations.

Acknowledgements: Thank are due to Fundação para a Ciência e Tecnologia (Portugal) and FEDER-COMPETE for financial support through Centro de Química (UID/QUI/00686/2013 and UID/ QUI/0686/2016), and a PhD grant to R.C.M. Ferreira (SFRH/BD/86408/2012). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased with funds from FCT and FEDER.

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