Photoinduced charge separation in pyrenedicarboxamide-linked DNA hairpins.

The synthesis and photophysical properties of the dihydroxypropylamide derivative of pyrene-1,6-dicaboxamide, its aniline dyad, and DNA conjugates are reported. The dicarboxamide serves as a hairpin linker for bis(oligonucleotide) conjugates having short base pair stems. The dihydroxypropyl derivative has a large fluorescence quantum yield and long singlet decay time, as determined by fluorescence and time-resolved broad band pump-probe spectroscopy. The aniline dyad undergoes exergonic charge separation with formation of a radical ion pair which decays via charge recombination. The highly characteristic transient absorption spectrum of the pyrene anion radical is used to monitor the dynamics of its formation and decay. The dicarboxamide-linked hairpin conjugates undergo charge separation with adjacent guanine and adenine bases. Charge separation with guanine is accompanied by efficient pyrene fluorescence quenching. In contrast, reversible charge separation with adenine results in multiple exponential fluorescence decay. The energetics and dynamics of charge separation are compared with those of other arenedicarboxamide DNA hairpin linkers.