A sensitive phosphorescent thiol chemosensor based on an iridium(iii) complex with α,β-unsaturated ketone functionalized 2,2′-bipyridyl ligand

Abstract

An iridium(III)-containing phosphorescent chemosensor Ir(ppy)(2)(L)(PF(6)) (1, ppy = 2-phenylpyridine) containing a 2,2'-bipyridyl ligand (L) functionalized with an alpha,beta-unsaturated ketone for selective detection of thiol was synthesized and characterized by spectroscopic and photophysical measurements. The structure of complex 1 was determined by X-ray crystallography. In order to get an insight into 1,4-addition reactions of thiol to complex 1, the adduct 2 from reaction of 1 with benzenethiol was successfully prepared and characterized. Complex 1 shows a lowest energy absorption at ca. 450 nm, primarily ascribable to an intraligand charge transfer (ILCT) transition from the HOMO (pi) resident on the fragment -C(O)C(6)H(4)N(C(2)H(5))(2) to the LUMO (pi*) localized on the 2,2'-bipyridyl moiety in the functionalized 2,2'-bipyridyl ligand as suggested from DFT computational studies. Complex 1 is weakly emissive at ca. 587 nm at ambient temperature, arising likely from the (3)ILCT excited state. Upon addition of thiol to a semi-aqueous solution of complex 1, the lowest energy absorption is obviously blue-shifted and the emission is remarkably enhanced due probably to a conversion from the primary ILCT state to the predominant [pi(ppy)-->pi*(L)] LLCT and the [5d(Ir)-->pi*(L)] MLCT state caused by the formation of the 1-thiol adduct. The sensing properties of 1 to thiol were also investigated by ESI-MS spectrometry and (1)H NMR spectroscopy.

Rational Design of Phosphorescent Chemodosimeter for Reaction‐Based One‐ and Two‐Photon and Time‐Resolved Luminescent Imaging of Biothiols in Living Cells

“…Scheme shows the synthetic route of complex 1 . The cyclometalated C^N ligand L was prepared by the reaction of acetophenone and 4‐(pyridin‐2‐yl)benzaldehyde through aldol condensation reaction . The dinuclear cyclometalated Ir(III) chloro‐bridged precursor [Ir(L) 2 Cl] 2 with L as cyclometalated ligand was synthesized using the same method as that reported by Nonoyama .…”

Crystal structure of [1,1′′′-bis(pyrimidin-2-yl)-4,4′:2′,2′′:4′′,4′′′-quaterpyridine-1,1′′′-diium-κ2N1′,N1′′]bis[2-(pyridin-2-yl)phenyl-κ2N,C1]iridium(III) tris(hexafluoridophosphate) acetonitrile trisolvate

“…The bite angle of the qpy-based ligand is 76.6 (2) , while those of the ppy ligands are slightly larger at 80.1 (6) and 80.8 (5) . As for other related complexes (Ladouceur et al, 2010;Zhao et al, 2010;Constable et al, 2013;Schneider et al, 2014), the strong trans effects of a -bonded phenyl ring (Coe & Glenwright, 2000) causes these units to adopt a cis orientation, so that the pyridyl rings of the ppy ligands are oriented trans. The structural trans effect of the phenyl rings is shown by the ca 0.08 Å lengthening of the Ir-N(qpy) distances [average = 2.132 (10) Å ] with respect to the Ir-N(ppy) ones [average = 2.05 (6) Å ].…”

“…Complexes of the form [Ir III (ppy) 2 (N-N)] + (N-N = 2,2 0 -bipyridyl or a related -diimine ligand) are well known, and many examples have been structurally characterized (e.g. Ladouceur et al, 2010;Zhao et al, 2010;Constable et al, 2013;Schneider et al, 2014).…”

An Ir(III) complex chemosensor for the detection of thiols

“…[39] Additionally, Chen’s group reported an iridium(III) complex thiol chemosensor based on an α,β-unsaturated ketone motif. [40] In this project, we sought to employ an iridium(III) complex for the detection of thiols based on the redox reaction between GSH and the N^N donor (phendione) of a luminescent iridium(III) complex. We anticipate that the reduction of phendione by thiols would influence the metal-to-ligand charge-transfer (MLCT) state of the iridium(III) complex, thereby allowing the complex to function as a luminescent chemosensor for thiols detection.…”