“…128 To overcome the above mentioned shortcomings of probe 10 we turned our attention to crown-ether functionalities as receptor units, because it has been demonstrated already with numerous examples that the direct attachment of azacrown ether units to a fluorophore is a general design principle for the development of donor-acceptor based fluorescent probes that change emission wavelength upon complexation of a metal ion (Scheme 1c). [3][4][5][6][7][8][9][10][11][12][122][123][124][125][126][127] Nevertheless, most crown ether host molecules do not bind the analyte to significant extent in water, 129 so that the majority of probes can only operate in non-competitive organic solvents. Therefore, we focused our studies on the 1,4-dioxa-7,13-dithia-10-azacyclopentadecane receptor unit, that is known to bind Hg 2+ ions in water with high affinity.…”