Communication: Photoactivation of nucleobase bound platinumII metal complexes: Probing the influence of the nucleobase

Abstract

We present UV laser action spectra (220-300 nm) of isolated nucleobase-bound PtII(CN)42- complexes, i.e., Pt(CN)42-·M, where M = uracil, thymine, cytosine, and adenine. These metal complex-nucleobase clusters represent model systems for identifying the fundamental photophysical and photochemical processes occurring in photodynamic platinum (II) drug therapies that target DNA. This is the first study to explore the specific role of the nucleobase in the photophysics of the aggregate complex. Each of the complexes studied displays a broadly similar absorption spectra, with a strong λmax ∼ 4.7 eV absorption band (nucleobase localized chromophore) and a subsequent increase in the absorption intensity towards higher spectral-energy (Pt(CN)42- localized chromophore). However, strikingly different band widths are observed across the series of complexes, decreasing in the order Pt(CN)42-·Thymine > Pt(CN)42-·Uracil > Pt(CN)42-·Adenine > Pt(CN)42-·Cytosine. Changes in the bandwidth of the ∼4.7 eV band are accompanied by distinctive changes in the photofragment product ions observed following photoexcitation, with the narrower-bandwidth complexes showing a greater propensity to decay via electron detachment decay. We discuss these observations in the context of the distinctive nucleobase-dependent excited state lifetimes.