Transient absorption and time-resolved vibrational studies of photophysical and photochemical processes in DNA-intercalating polypyridyl metal complexes or cationic porphyrins

Recent advances in the use of transient absorption (TA) and time-resolved vibrational spectroscopies (TRIR and TR3) to study both excited states and reaction intermediates in metal complexes and porphyrins which intercalate into DNA are reviewed. A particularly well-studied class of compounds, which nicely illustrates the comparative advantages of these techniques, is that of ruthenium dppz complexes where the complex might show light-switching or photo-oxidising behaviour depending on the nature of the ancillary ligand. Comparative data on Re- and Cr-dppz complexes are also considered. In the second part of this review transient studies of porphyrins, which are known to intercalate into DNA, are considered with particular emphasis on tetramethyl-pyridiniumporphyrins, where the photophysical behaviour of the metal-free and various metal derivatives are compared.