In one most preferred embodiment, the dye is {TAIL ~ N N} {HEAD ~ 3,3,3,3 tetramnethylbenzindodicarbocyanine}, which has the formula: ##STR3## 
In one most preferred embodiment , the dye is { TAIL ~ N N } { HEAD ~ 3,3,3,3 tetramnethylbenzindodicarbocyanine } , which has the formula : # # STR3 # #
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH