Displacement of the chloro group in 49a and 49b with iodide afforded the corresponding isomeric iodopropylsilyl dyes 52a and 52b (Scheme 3), which could be further elaborated by reaction with a wide variety of nucleophiles. Azide-functionalized dyes 55a and 55b were readily synthesized (Scheme 3), and reacted rapidly with strained dibenzocyclooctyne (DBCO) reagents in copper-free click chemistry reactions (Scheme S1). Reaction of 52a-b with the phenol of Hoechst 33258 allowed direct incorporation of this DNA-binding dye (68a-b, Figure ). Additional Si-bridge elaboration allowed introduction of an NHS ester (Figure ), chloroalkane ligands for the protein HaloTag 39 (Figure ), and O 6 -benzylguanine ligands for SNAP-tag 40 (Figure ). These reagents all hold considerable potential for labeling of biomolecules with bright, photostable near-IR dyes, and we anticipate that Si-iodopropylsilyl dyes can be readily elaborated with many other nucleophiles.