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Calix[4]azacrowns as Novel Molecular Scaffolds for the Generation of Visible and Near-Infrared Lanthanide Luminescence
文摘
Two calix[4]azacrow ns, capped with two ami nopolyamide bridge s, were u sed a s liga nd s for the complexatio n ofla ntha nide io ns [Eu(III), Tb(III), Nd(III), Er(III), La(III)]. The formatio n of 1:2 a nd 1:1 complexe s wa s ob served, a nd stability co nsta nt s, determi ned by UV ab sorptio n a nd fluore sce nce spectro scopy, were fou nd to be ge nerally o nthe order of log s/gifchars/beta2.gif" BORDER=0 ALIGN="middle">11 ![](/image<font color=) s/e ntitie s/ap.gif"> 5-6 a nd log s/gifchars/beta2.gif" BORDER=0 ALIGN="middle">12 ![](/image<font color=) s/e ntitie s/ap.gif"> 10. The structural cha nge s of the liga nd s upo n La(III) complexatio n wereprobed by 1H NMR spectro scopy. The two liga nd s were ob served to have oppo site fluore sce nce behavior s, namely,fluore sce nce e nha nceme nt (via blocki ng of photoi nduced electro n tra nsfer from ami ne group s) or que nchi ng (viala ntha nide-chromophore i nteractio ns) upo n metal io n complexatio n. Lo ng-lived la ntha nide lumi ne sce nce wa sse nsitized by excitatio n i n the ![](/image<font color=) s/gifchar s/pi.gif" BORDER=0 >, ![](/image<font color=) s/gifchar s/pi.gif" BORDER=0 >* ba nd of the aromatic moietie s of the liga nd s. The direct i nvolveme nt of thea nte nna triplet state wa s demo nstrated via que nchi ng of the liga nd pho sphore sce nce by Tb(III). Ge nerally, Eu(III)lumi ne sce nce wa s weak ( s/gifchars/Phi.gif" BORDER=0 >lum ![](/image<font color=) s/e ntitie s/le.gif"> 0.01%) a nd much shorter lived ( s/gifchars/tau.gif" BORDER=0 >lum = 0.36 m s) tha n the Tb(III) emi ssio n. Thelatter, o n the other ha nd, reached lifetime s of up to 2.60 m s a nd qua ntum yield s a s high a s 12% for o ne of theliga nd s. Water/deuterium oxide excha nge experime nt s showed the pre se nce of o nly o ne solve nt molecule i n thecoordi natio n sphere of the la ntha nide s. However, Eu(III) lumi ne sce nce wa s efficie ntly que nched by NH o scillator sa nd the pre se nce of a liga nd-to-metal charge tra nsfer state. Near-i nfrared lumi ne sce nce of Nd(III) wa s al so ge neratedby e nergy-tra nsfer se nsitizatio n.
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