An electro-optic element includes a first substrate defining first and second surfaces and a second substrate defining third and fourth surfaces. A first electrically conductive layer is disposed on the second surface and a second electrically conductive layer is disposed on the third surface. An electrochromic medium is disposed in a cavity between the first and second substrates, the electrochromic medium including an anodic component and a cathodic component. At least the anodic component is configured to reversibly attenuate transmittance of light having a wavelength within a predetermined wavelength range when in an electrochemically activated state. The anodic component includes a substituted ketal phenazine compound.