ImplodingEmitter.cs

public class ImplodingEmitter : MonoBehaviour {
    void Start() {
       StartCoroutine(Implode());
    }
 
    IEnumerator Implode() {
       if (!particleSystem.isPlaying) {
         particleSystem.Play();
       }
 
       //let the system do it's thing for a bit
       yield return new WaitForSeconds(3f);
 
       //stop emission
       particleSystem.emissionRate = 0f;
 
       //allocate reference array
       ParticleSystem.Particle[] particles = new ParticleSystem.Particle[particleSystem.particleCount];
 
 
       //this loop executes over several frames
       // - get particle list
       // - update each particle's position
       // - set particle list
       // - wait one frame
       for (float t = 0f; t < 1f; t += 0.1f) {
         int count = particleSystem.GetParticles(particles);
         for (int i=0; i<count; i++) {
          particles[i].position = Vector3.Lerp(particles[i].position, transform.position, t);
         }
         particleSystem.SetParticles(particles, count);
 
         yield return null;
       }
 
       //once loop is finished, clear particles
       particleSystem.Clear();
    }
}