Semibluffing the turn

Is semibluffing profitable in the turn in a 1/2$ game shorthanded?

I got a flush draw Ace high and raise the turn heads up in a semibluff, with trhhe hearts on the table the man called my raise and bet the river anyway then i folded.

A second example is that i had a open ended straigh draw and no overcards in my pocket i was almost sure he hasnt anything big, then i raise the turn and he calls. In the river the straigh didnt come i bet again in a pure bluff only to be called and lose 2$ more agains a pair of 4 (being several overcards on the flop) i ask wheter against so extremely loose players it is simply better to raise te turn only to see a free showdown.