I'd say 'No', as a result of the following:
First, "hit" is really just a short-hand for "hit hard enough to deal damage". The game is agnostic to whether a "miss" is due to them actually moving out of the way of your attack or because your attack went *ping* on their armor; both count equally as a "miss". This means that, even if you are holding the charge on a Touch attack, you cannot deliver it with an unarmed strike on the premise that you didn't appreciably deal damage, but you didn't miss outright; there is no allowance in the rules for this.
Secondly, even regarding a Touch attack, a trip is not sufficient to deliver the spell. You require an additional feat, for instance, Tripping Staff, to allow a Magus to deliver a spell via spellstrike with their quarterstaff. If the contact due to tripping were sufficient to deliver a touch spell, such a feat would be superfluous.
Based on this evidence, we can conclude that "strike" doesn't just mean "any contact" as would be implied by the normal definition of the term, but we must look at it in the context of the Pathfinder system that it would mean, "appreciably strike", in which case, means a "hit" for the purpose of dealing damage in combat. You cannot casually caress them across the cheek with a Cruel weapon and trigger the ability and, just the same, you cannot use the weapon as a tripping implement to the same effect.
