Photophysical Properties of Quinolizinium Salts and Their Interactions with DNA in Aqueous Solution

The photophysical properties of three quinolizinium salts (naphto[2,1-b]quinolizinium bromide (Q2), naphto[1,2-b]quinolizinium bromide (Q3), and indolo[2,3-b]quinolizinium tetrafluoroborate (HI)) in fluid media and their interactions with DNA were investigated by steady-state and by nanosecond and femtosecond time-resolved techniques. The main decay pathways of the excited singlet state S(1), fluorescence, intersystem crossing, and internal conversion, were characterized in terms of quantum yields and rate constants. The lowest triplet state of the quinolizinium salts is able to sensitize singlet oxygen in rather high efficiency (phi(Delta) = 0.4 to 0.5 in MeCN). The complexes between quinolizinium salts and DNA formed in the ground state were characterized in terms of lifetimes and decay channels to give more details of the mechanism of photoinduced DNA strand break.