Mount a fully articulated tv mount with only one stud
Your best bet to assure that the fully articulated TV mount is secure and will operate correctly is to mount a large piece of 3/4" thick plywood across the wall in the back of the recessed area. Make sure this plywood spans across at least the three studs in the wall and even better if you put it full width and pickup the corner studs as well. Screw the plywood to the studs with heavy duty screws at least 3 or 4 per stud. The plywood can be sanded, primed and painted to match the wall. Behind the TV you will barely see it there, but when you do you will reset assured that you have the best secure mount possible. 

Trying to use toggle bolts into just drywall is not a secure proposition. Fully articulated mounts can put a huge amount of torque on the TV bracket when extended and pulled out. This can rip the toggle bolts right out of the drywall. Use the thick plywood as described above and distribute the forces of the bracket torque across a significant portion of the wall structure. And by the way, plywood has fantastic screw holding strength when used with proper sized pilot drilling.