Solvent- and environment-dependent fluorescence of modified nucleobases

Fluorescent nucleosides with modified nucleobases are useful tools for detecting nucleic acids and probing their structures and functions. Nucleobases are suitable for modification because 1) intrinsically light-absorbing nucleobases can be converted to fluorescent chromophores by simple chemical modification, 2) attaching substituents to nucleobases at appropriately selected positions does not inhibit base pairing or duplex formation, and 3) duplex formation and protein interactions affect the environment of nucleobases, causing changes in their fluorescence intensities and/or wavelengths. This review summarizes recent fluorescent nucleosides and their photophysical properties, such as absorption wavelength, emission wavelength, and fluorescence quantum yield together with their solvent dependency.