Want to change an icon in the toolbar when its clicked

So I made a plugin. I have the "exec" command working just fine. I have it loading my icon normally. What I want to do, is when the icon is clicked, the icon changes to a loading gif that I have. 

I tried this with no luck:

exec : function(editor)
{
    editor.ui.items.CustomIcon.icon = this.path + 'icons/loading.gif';
}

any help here would great!