
TY  - JOUR
A1  - Geue, Jason P. 
A1  - Head, Nicholas J. 
A1  - Ward, A. David 
A1  - Lincoln, Stephen F. 
T1  - The Formation of Fluorescent Alkaline Earth Complexes by 4-{2-[10-(2-Morpholinoethyl)-9-anthryl]methyl}morpholine and its -Ethyl}morpholine and -Propyl}morpholine Analogues in Acetonitrile
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 2003
VL  - 56
IS  - 4
SP  - 301
EP  - 307
KW  - 
UR  - https://doi.org/10.1071/CH02231 
N2  - The formation of fluorescent alkaline earth complexes of 4-{2-[10-(2-morpholinoethyl)9-anthryl]methyl}morpholine and its new -ethyl}morpholine and -propyl}morpholine analogues, L = (1)&#8211;(3), in acetonitrile is reported. Each L has a &#8216;fluorophore&#8211;spacer&#8211;receptor&#8217; structure in the sequence &#8216;anthracene&#8211;(methylene)n&#8211;morpholine&#8217; in which quenching of the anthracene fluorophore becomes less effective as the receptor tertiary nitrogen becomes more distant with an increase in n from 1 to 3. Complexation by the alkaline earths (M2+) modulates photoinduced electron transfer (PET) and enhances the fluorescence of (1)&#8211;(3). The two alkyl morpholine receptors of (1)&#8211;(3) may either complex M2+ singly to form [ML]2+ and [M2L]4+ or cooperatively to form a [ML&#8242;]2+ &#8216;sandwich&#8217; complex depending on the length of the alkyl spacer. Thus, (1) dominantly forms [ML]2+ and [ML&#8242;]2+ while (2) and (3) form all three complexes as exemplified by [Mg(2)]2+ and [Mg(2)&#8242;]2+ characterized by the overall complexation constant K1 = 9.19 &#215; 104 dm3 mol&minus;1 and [Mg2(2)]4+ characterized by the stepwise complexation constant K2 = 1.19 &#215; 103 dm3 mol&minus;1 at 298.2 K and I = 0.05 mol dm&minus;3 (NEt4ClO4). The most stable and fluorescent complexes are formed by Mg2+ and Ca2+, consistent with M2+ size being an important factor affecting complex characteristics. Eighteen complexation constants and quantum yields are reported for the (1)&#8211;(3) complexes together with those for (1)&#8211;(3) alone. In 40 : 60 (v/v) 1,4-dioxan/water, protonation modulates PET to increase the fluorescence of (1)H22+&#8211;(3)H22+. (The pKa values for (2)H22+ are 6.38 and 5.62, and for (3)H22+ are 7.00 and 6.25.) The syntheses of (2) and (3) are reported. 
ER  -

