Why is my 2D collision not working?

So I have a rigid body 2D and a circle collider 2D on my player sprite (the green one) and a Polygon Collider 2D on an other (player is standing on an orange thingy). Both are triggers. To test if they work I added a debug line but if I walk over the other collider nothing happens. On the Z-axis the two sprites don't have the same value, but that shouldn't matter in 2D mode right?

     void OnCollisionEnter2D(Collision2D col) {
         Debug.Log ("It works!")
     }

I really can't see what I am doing wrong!