In {HEAD ~ a second most preferred embodiment}, {TAIL ~ the dye} is N N 3,3,3, 3 tetramethylbenzindodicarbocyanine, which has 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  
In { HEAD ~ a second most preferred embodiment } , { TAIL ~ the dye } is N N 3,3,3 , 3 tetramethylbenzindodicarbocyanine , which has 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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