Smoothing the characters rotation with Lerp

Hey! I have a character, which will turn to face a certain direction when not moving. Currently the rotation after the character stops moving happens very fast, which looks ugly. So I'm trying to smooth it out with Lerp.

I've tried to code it but its currently not working, it doesn't give any errors but some of you might see whats wrong here.

public Quaternion dir;
public float smoothSpeed = 0.5f;

void Update () {
    if(Input.GetAxis("Vertical")==0 && Input.GetAxis("Horizontal")==0)
    {
        dir.y=-135;

        transform.rotation = Quaternion.Lerp(transform.rotation, dir, Time.deltaTime * smoothSpeed);
    }
}

}

The direction is right, but it is still doing the rotation instantly.

change

transform.rotation = Quaternion.lerp

to

transform.rotation = Quaternion.Slerp

Here is the Final Code:

using UnityEngine;
using System.Collections;

public class Smoothrotatoin : MonoBehaviour {

	public Quaternion dir; 
	public float smoothSpeed = 0.5f;
	
	void Update () { if(Input.GetAxis("Vertical")==0 && Input.GetAxis("Horizontal")==0) { dir.y=-135;
			
			transform.rotation = Quaternion.Lerp(transform.rotation, dir, Time.deltaTime * smoothSpeed/100);
		}
		
	}
	
}