## The frightened effect ends when the spell ends, and the spell ends when you cast another concentration spell. 

*Wrathful smite* states that the target is

> frightened of you until the spell ends. 

So when the spell ends, they stop being frightened, and if you stop concentrating, the spell ends immediately. *Tasha’a Cauldron* contains a helpful list of rules summaries, one of which explains succinctly the rules for concentration:

> As soon as you start casting a spell or using a special ability that requires concentration, your concentration on another effect ends instantly

So casting a different spell that requires concentration will end the effects of *wrathful smite* immediately, and the target will no longer be frightened. The full rules, found in the PHB, reads:

>  The following factors can break concentration:
>
> * **Casting another spell that requires concentration.** You lose concentration on a spell if you cast another spell that requires concentration. You can't concentrate on two spells at once.
>
> * [other stuff that ends concentration]