Patent ID: 7491830

Claim:
A fluorescent lipophilic phenyl xanthene dye according to structural formula (I): wherein: Rh is a rhodol-type xanthene ring system that is substituted at the exocyclic amine group with an optionally substituted lipophilic (C4-C20) alkyl group, or a rhodamine-type xanthene ring system that is substituted at an exocyclic amine group with an optionally substituted lipophilic (C4-C20) alkyl group; and R 11 , R 12 , R 13 , R 14 and R 15 are defined according to one of the following alternatives: (i) R 11 and R 15 are each the same halo group and R 12 , R 13 and R 14 are each hydrogen; (ii) R 11 , R 13 and R 15 are each the same halo group and R 12 and R 14 are each hydrogen; (iii) R 11 , R 12 , R 14 and R 15 are each the same halo group and R 13 is hydrogen; or (iv) R 11 , R 12 , R 13 , R 14 and R 15 are each the same halo group.