Cu2+ Colorimetric Sensing and Fluorescence Enhancement and Hg2+ Fluorescence Diminution in "Scorpionate"-like Tetrathienyl-Substituted Boron-Dipyrrins

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• 作者：Shin Hei Choi ; Keliang Pang ; Kibong Kim ; David G. Churchill
• 刊名：Inorganic Chemistry
• 出版年：2007
• 出版时间：December 10, 2007
• 年：2007
• 卷：46
• 期：25
• 页码：10564 - 10577
• 全文大小：921K
• 年卷期：v.46,no.25(December 10, 2007)
• ISSN：1520-510X

文摘

Four novel tetrathienyl-substituted boron-dipyrrin-type (BODIPY-type) complexes, 3-(R')-4,4-di(R')-8-R-4-bora-3a,4a-diaza-s-indacene (4a, R = 2-T, R' = 2-T; 4b, R = 3-T, R' = 2-T; 5a, R = 2-T, R' = 3-T; 5b, R = 3-T,R' = 3-T; T = thienyl) have been prepared and fully characterized to explore patterns of stoichiometric Mⁿ⁺recognition in solution. Treatment of the respective parent BF₂ dipyrrin with 2- or 3-thienyllithium gave the unexpectedasymmetric tetrathienyl-substituted products in 8.5-35% yield. Compounds 4a and 4b bear a neutral "scorpionate"-like [SSS] tridentate binding pocket. Extensive NMR and UV-vis spectroscopic studies were performed on 4a-5b;5a, 4b, and 5b were structurally characterized. The _F values for 4a-5b all decrease compared to the BF₂-containing parent molecules (0.00058, 0.012, 0.00090, and 0.0051, respectively), with _abs,max values (, M^-1 cm^-1)of 563 (44 000), 553 (29 000), 539 (33 000), and 531 (44 000) nm, respectively, and Stokes' shifts of 25-36 nm.Upon treatment with metal ion (Ca²⁺, Cs⁺, Mn²⁺, Co²⁺, Cu²⁺, Ag⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺) perchlorate salts, thesolution of 4b undergoes rapid pink-to-clear switch-off behavior upon Cu²⁺ addition (10 M scale) with smallereffects seen for 4a. Further, there were 2- to 19-fold Cu²⁺ fluorescence enhancements for these ligands. Cu²⁺-and Hg²⁺-L (L = 4a-5b) binding was modeled, and response patterns for Mⁿ⁺-L 1:1 molar solutions upon Cu²⁺addition were measured. Upon treatment with Hg²⁺, all ligand solutions show a significant fluorescence decreaseaccompanied by minor absorption increases. The UV-vis spectroscopic detection limit for Cu²⁺ and Hg²⁺ is ~270ppb and ~1.7 ppm, respectively; the naked eye detection limit for Cu²⁺ with 4b (1.0 × 10^-5 M) is ~23 M. DFTcalculations gave HOMO-LUMO gaps of 478 (4a), 462 (4b), 448 (5a), and 442 nm (5b). Molecular orbital diagramsfor 4a-5b revealed that the HOMO and LUMO electron density is distributed onto the 3-position-thienyl group andto a lesser degree the B(thienyl)₂ moiety.