We report on the first stage of our theoretical study of the quino[2,3,4-kl]acridinium,1,13-dimethoxy-5,9-dipropyl-cation. This molecule, involved in the synthesis of novel triazaangulenium dyes of high chemical stability, is a chiral [4]-helicenium. The structure and the IR spectrum of the quino[2,3,4-kl]acridinium,1,13-dimethoxy-5,9-dimethyl-cation derived from theoretical calculations which use various density functional theory methods, are compared with the geometry derived from X-ray diffraction measurements and the experimental IR spectrum. Our study shows that the chosen variant of DFT methods (Becke88 for exchange, P86 for correlation, 3-21G** basis set) reproduces the experimental geometry within 0.004 Å and the IR frequencies within 15 cm−1.