Positive charges and substituent size in TPM dyes may be two important factors in influencing the binding stability of the dyes and G-quadruplexes.

In addition to the familiar duplex DNA, certain G-rich DNA sequences can fold into a variety of four-stranded structures, which are called G-quadruplexes.

The results show that the fluorescence spectra of four TPM dyes can be used to discriminate intramolecular G-quadruplexes from intermolecular G-quadruplexes, single-and double-stranded DNAs.