X-ray attenuating compositions and methods

A method of enhancing x-ray attenuation of an x-ray attenuating compound, comprising

• a) choosing a molecule capable of modulating from a first conformational state to a second conformational state in response to an external stimulus,
• b) determining a first interatom distance between a first k-edge atom and a second k-edge atom in the first conformational state within a first harmonic error of 0 to about 0.2,
• c) determining a second interatom distance between the first k-edge atom and the second k-edge atom in the second conformational state within a second harmonic error of about 0.8 to 0.99,
• d) attaching the first k-edge atom to the molecule at a first position, and
• e) attaching the second k-edge atom to the molecule at a second position,
• wherein the first position and the second position provide the first interatom distance in the first conformational state and the second interatom distance in the second conformational state.