2D Collider Isnt working


Im not sure what I am doing wrong, as the code works on a 3d object. I have tryed applying it to a UI image that is set in screen space, but it isnt picking up being clicked on can anyone help me with why it isnt working.

using UnityEngine;
using System.Collections;

public class ExitScript : MonoBehaviour {

	DisplayBoxInitializer boxInitializer;
	GameObject Exit ;

	public CharacterMotor charactermotor;
	public Player player;
	public MouseLook mouselook;

	// Use this for initialization
	void Start () {
	// Update is called once per frame
	void Update () {

	void OnMouseDown (){
		charactermotor.enabled = true;
		mouselook.enabled = true;
		//player.enabled = true;
		Screen.lockCursor = true;
		GetComponent<Renderer>().material.color = Color.red;
		StartCoroutine ("wait");
		//Exit.enabled = false;
	IEnumerator wait(){
		yield return new WaitForSeconds (0.5f);
		player.enabled = true;


As per the manual, the OnMouseDown event is only sent through the GUIElement and Collider components. Collider2D does not trigger this event.