Nonpolar thymidine analogs are provided comprising a dihalogenated or trihalogenated base of the structure: ##STR00001## where R.sub.1 is a sugar moiety; R.sub.2 is H or CH.sub.3; an imaging moiety or a cytotoxic moiety and X.sub.1 and X.sub.2 are independently selected from I, Cl, Br, and F, with the proviso that not more than one F will be present at these positions.