A highly selective turn-on colorimetric and luminescence sensor based on a triphenylamine-appended ruthenium(II) dye for detecting mercury ion

Abstract A dual colorimetric and luminescent sensor based on a heteroleptic ruthenium dye [Ru(Hipdpa)(Hdcbpy)(NCS) 2 ] – ·0.5H +  0.5[N(C 4 H 9 ) 4 ] + Ru(Hipdpa) {where Hdcbpy = monodeprotonted-4,4′-dicarboxy-2,2′-bipyridine and Hipdpa = 4-(1 H -imidazo[4,5- f ][1,10]phenanthrolin-2-yl)- N , N -diphenylaniline} for selective detection of Hg 2+ is presented. The results of spectrophotometric titrations revealed an evident luminescence intensity enhancement ( I / I 0  = 11) and a considerable blue shift in visible absorption and luminescence maxima with the addition of Hg 2+ . The sensitive response of the optical sensor on Hg 2+ was attributed to the binding of the electron-deficient Hg 2+ to the electron-rich sulfur atom of the thiocyanate (NCS) ligand in the Ru(Hipdpa), which led to an increase in the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Accordingly, the blue shift in the absorption spectrum of Ru(Hipdpa) due to the binding of Hg 2+ was obtained. Ru(Hipdpa) was found to have decreased Hg 2+ detection limit and improved linear region as compared to di(tetrabutylammonium) cis -bis(isothiocyanato)bis(2,2′-bipyridine-4-carboxylic acid-4′-carboxylate)ruthenium(II) N719. Moreover, a dramatic color change from pink to yellow was observed, which allowed simple monitoring of Hg 2+ by either naked eyes or a simple colorimetric reader. Therefore, the proposed sensor can provide potential applications for Hg 2+ detection.