Disclosed is a compound having the following structure: TIFF2023537627000024.tif61169X is an anion (e.g., a biologically relevant anion such as
chloride,
iodide, etc.); Y is NH, NR 10 , or CR 11 R 12 where Z is a
heteroatom (e.g., O, S, or Se), and R and R 1 are independently selected from methyl, ethyl, propyl (e.g., n-propyl,
isopropyl), butyl (e.g., n-butyl, isobutyl, tert-butyl), and the like, and combinations thereof. In various examples, R and R 1 At least one of the atoms is not an
oxygen atom (both cannot be
oxygen atoms to form -NO2). 2 and R 3 R is independently selected from methyl, ethyl, propyl (e.g., n-propyl,
isopropyl), butyl (e.g., n-butyl, isobutyl, tert-butyl), etc., and combinations thereof. 4 , R 5 , R 6 , R 7 , R 8 , R 9 , R 10 , R 11 , R 12 are independently selected from
hydrogen,
alkyl groups (e.g., methyl, ethyl, propyl (e.g., n-propyl,
isopropyl), butyl (e.g., n-butyl, isobutyl, tert-butyl), etc.), and combinations thereof. Also disclosed are compositions and methods of using the compounds and compositions. The compounds or compositions can be used to visualize or identify tumors.