Control of On-Off or Off-On Fluorescent and Optical [Cu(2+)] and [Hg(2+)] Responses via Formal Me/H Substitution in Fully Characterized Thienyl "Scorpionate"-like BODIPY Systems

Abstract

One 8-phenyl and two 8-mesityl-substituted "scorpionate"-like BODIPY-type species of the formula [3,4,4-tris(S-R-(2-thieny))-8-(2,4,6-k-phenyl)-4-bora-3a,4a-diaza-s- indacene (R = H, R' = H, 3a; R, = H, R' = Me, 2a; R, = Me, R' = Me, 2b)] have been synthesized and fully characterized. Importantly, differences in their solution (MeCN) optical Cu2+ and Hg2+ probing capacity via SSS-chelation were investigated. Compounds 2a-3a were prepared from the requisite 8-substituted BODIPY complexes. They were characterized first by complete H-1, B-11 and C-13 NMR spectroscopic assignments (CD3Cl or CD3C(O)CD3); the molecular structures of 2a and 3a were determined by X-ray crystallography. Compounds 2a-3a were studied by UV-vis and fluorescence spectroscopy [Phi(F) = 0.27 +/- 0.013 (2a); 0.024 +/- 0.0016 (2b); 0.0034 +/- 0.00047 (3a)]. Importantly, low [Cu2+] with 3a (<3.0 x 10(-5) M) gave rise to an increase of fluorescence intensity (off-on; 6.3-fold), whereas with 2a it decreased (on-off). When [Hg2+] (<3.0 x 10(-5) M) was added to,213, the lambda(em,max) value increased (off-on; 3.2-fold), and for 2a, it decreased (on-off). The association constant (K-a) for Hg2+ . 2a was determined to be 3120 +/- 307 M-1. An approximate stoichiometric 1:1 binding determined by Job plot analysis is in line with successful DFT modeling of SSS-Cu2+ binding for this system type. H-1 NMR spectroscopy also revealed tentative sets of product complex peaks. These simple differences caused by formal ligand Me-group incorporation are the first for any related fluorophores, to the best of our knowledge.