The DNA Duplex as an Aqueous One-Dimensional Soft Crystal Scaffold for Photochemistry

In this account, we demonstrate that DNA duplex is an ideal scaffold for photochemistry, particularly for comparison of photochemical theory with experiments. The well-defined structure of a DNA duplex can be regarded as an aqueous one-dimensional soft crystal composed of a chromophore-like base-pair assembly. When any base pair in the duplex is replaced with a chromophore, orientation, distance, and association number of chromophores can be precisely controlled. We have developed a new methodology for introduction of chromophores into DNA duplexes using D-threoninol. By using the DNA duplex as a scaffold, experiments on exciton interactions of chromophore assemblies can be compared with molecular exciton theory. A fluorescent resonance energy transfer (FRET) system was also constructed by introducing donor pyrene and acceptor perylene into the DNA duplex using D-threoninol monomers. Using this system, we demonstrated orientation-dependent FRET. We found that theories on both exciton interaction and FRET qualitatively coincide with experimental data and revealed the limitation of the point-dipole approximation. We also evaluated the intrinsic quantum yield of photodimerization of stilbene derivatives by suppressing a side reaction. We propose that there is a correlation of quantum yield of photodimerization with the energy gap of HOMO or LUMO, a hypothesis that deserves theoretical investigation.