Energy doesn't scale with distance in that way, with quantum mechanics. A "mismatch in size" (roughly speaking) will result in a different quantum efficiency, not a lowered energy, and also keep in mind that DNA is a highly coiled molecule so the resonance frequency could be deceptive. The straightened length of DNA in a cell is on the length order of meters. (Though that doesn't mean that it will resonate with meter long waves, it will have a higher efficiency with wavelengths much longer than a micron)