Drugs like sufentanil, alfentanil, fentanyl and other opiates although belong to phenyl piperidine group like pethidine (meperidine), their spectrum of action is more morphine-mimicking, more like mediated through β endorphin and t receptors.
Actually there are some very striking differences between the two:
Fentanyl and other opiates unlike, morphine, is very highly lipid soluble, so has rapid onset and recovery. This again is due to rapid redistribution in fat and muscle. As a result of this, very rapidly crosses blood-brain barrier.
It is totally devoid of any cardiac effects, neither inhibitory nor excitatory. May produce bradycardia. Sufentanil and alfentanil have similar spectrum of activity as that of fentanyl.