Small molecules targeting telomeric DNA or its interactions with telomerase have been an active area of cancer research. In the present study, we investigated the interactions of six benzimidazole compounds, called azacyanines, differing from each other in alkyl chain length and branching in the benzimidazole ring (azamethyl, azaethyl, azapropyl, azaisopropyl, azabutyl, and azaisobutyl) with human telomeric DNA (tel24) in 1:1 and 1:6 ratio (tel24:azacyanine) using UV-Vis, circular dichroism (CD), and fluorescence spectroscopy. All the compounds were binding to tel24 as indicated by the formation of the weak induced CD band between 320 nm and 360 nm. A substantial red shift and hypochromic effect were observed in the UV-Vis spectrum of azamethyl or azabutyl upon binding to tel24. No red shift or hypochromic effect was observed in the spectrum of azaisopropyl. The denaturation temperature (T-m) of tel24 increased the most, from 65 degrees C to 78 degrees C, in the presence of azabutyl in 1:6 ratio. Azaisopropyl stabilized tel24 the least under the same conditions. The highest (7.84 x 10(5) +/- 3.44 x 10(4) M-1) and the lowest (2.04 x 10(5) +/- 5.38 x 10(4) M-1) association constants were obtained for azabutyl and azaisopropyl, respectively, by fluorescence spectroscopy. Overall, the benzimidazole scaffold, the one-pot synthesis, and the stabilization ability of azacyanines to tel24 make them plausible drug candidate molecules in targeting G-quadruplexes.