Long-lived excited state dynamics of i-motif structures probed by time-resolved infrared spectroscopy

UV?generated excited states of cytosine (C) nucleobases are precursors to mutagenic photoproduct formation. The i?motif formed from C?rich sequences is known to exhibit high yields of long?lived excited states following UV absorption. Here the excited states of several i?motif structures have been characterized following 267?nm laser excitation using time?resolved infrared spectroscopy (TRIR). All structures possess a long?lived excited state of ?300?ps and notably in some cases decays greater than 1?ns are observed. These unusually long?lived lifetimes are attributed to the interdigitated DNA structure which prevents direct base stacking overlap