make object rotate towards its direction after bounce

Well i guess ill answer this myself. I managed to solve it and no, Vector3.reflect() is not needed. The key is to track the original direction of the object as a Vector3 while also tracking the new direction in a seperate Vector3 after collision.

     Vector3 newDir = new Vector3(transform.position.x, transform.position.y, 0);
     float newDirValue = Mathf.Atan2(newDir.y - currDir.y, newDir.x - currDir.x);
     float newDirValueDeg = (180 / Mathf.PI) * newDirValue;
     transform.rotation = Quaternion.Euler(0, 0, newDirValueDeg);

This will calculate and set the transform.rotation.z of the object in the new direction its taking. currDir is the name of the Vector3 variable that keeps track of the original direction before collision.

     void FixedUpdate()
     {
         currDir = new Vector3(transform.position.x, transform.position.y, 0);
     }

This part is important considering physic simulations (the bounce material) is called before OnCollisionEnter(). However, OnCollisionEnter() is called within FixedUpdate(). This allows the values of currDir to be utilized in the collision code before the values of currDir became identical to newDIr.