Dendronised Ni(II) porphyrins as photoswitchable contrast agents for MRI

Light-responsive contrast agents for magnetic resonance imaging (MRI) based on Ni(II) porphyrin molecular spin switches have recently been introduced. We present their implementation in water and methanol based gels leading to the first soft materials that are rewritable with light and readable with MRI. Light of two different wavelengths as non-invasive stimuli can be applied to switch MRI contrast on and off, with a high spatiotemporal resolution and without fatigue.