Alkynyl Ruthenium Colorimetric Sensors:  Optimizing the Selectivity toward Fluoride Anion

Abstract

We report on the synthesis of alkynyl ruthenium colorimetric sensors whose receptors are constituted by thiazolidinedione, rhodanine, or barbituric heads as recognition centers for anions. As modifications in the charge density at these recognition centers affect the whole molecule, through the alkynyl ligand acting as a communicating wire, the effects of hydrogen-bonding interactions with the anions were observed with the naked eye and monitored by UV-vis absorption spectrometry. The selectivity of the sensors was improved through electronic modifications of the alkynyl ruthenium subunit: the higher the electron density at the receptor head, the higher the selectivity is. TD-DFT calculations rationalize the long-range electronic communication as a main characteristic of the alkynyl ruthenium species and as a key to improve the selectivity of alkynyl ruthenium-based sensors toward anions.

A simple synthesis of trans-RuCl(CCR)(dppe)2 complexes and representative molecular structures

“…The chemistry of transition metal complexes transRuCl(C"CR)(dppe) 2 is very well established [1][2][3][4][5][6][7][8][9][10], with a considerable body of recent research demonstrating the utility of these moieties in the construction of multimetallic complexes [11][12][13][14][15], optical materials [16][17][18], including those that exhibit pH or redox-switchable NLO response [19][20][21][22][23][24][25], colormetric [26] and fluorescent [27] sensing behaviour, the ''wire-like" behaviour that arises from extensive d-p mixing along the Ru-C"C fragment [28][29][30][31][32][33][34][35][36][37], and other characteristics that make these compounds potentially useful molecular electronic components [5,33,34,[38][39][40][41]. The facile replacement of the chloride ligand in complexes trans-RuCl(C"CR)(dppe) 2 either directly or from related vinylidenes with a second alkynyl ligand is well documented …”

Flavonol based ruthenium acetylides as fluorescent chemosensors for lead ions

“…These properties arise as a result of overlap between the d-orbitals of ruthenium and the conjugated p system and can thus be modified systematically either through variation of the organic p system or by fine-tuning the electron richness of the alkynyl ruthenium moiety itself. We already established that alkynyl ruthenium complexes bearing terminal hydrogen-bond receptors can also act as efficient anion sensors exhibiting large guest-induced colour changes and show high selectivity to fluoride ions [24].…”

Chromo- and Fluorogenic Organometallic Sensors

“…Similarly, a series of Ru(II) alkynyl complexes (7c-7g; Fig. 7) show a dramatic À , Cl À and Br À , although selectivity for F À is evident, and there is a dependence on the electron density on the appended functional group [68]. Bucking this trend, a series of luminescent cyclometallated Ir(III) poly-pyridine thiourea complexes (7h-7p; Fig.…”