In a second most preferred embodiment, the dye is N N 3,3,3, {HEAD ~ 3 tetramethylbenzindodicarbocyanine}, which has {TAIL ~ the formula}: ##STR4## These two dyes are preferred because they have commercially available precursors for the linking groups: 6 bromohexanol, 6 bromohexanoic acid and 1,4 butane sultone  
has
In a second most preferred embodiment , the dye is N N 3,3,3 , { HEAD ~ 3 tetramethylbenzindodicarbocyanine } , which has { TAIL ~ the formula } : # # STR4 # # These two dyes are preferred because they have commercially available precursors for the linking groups : 6 bromohexanol , 6 bromohexanoic acid and 1,4 butane sultone
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