Sugar free energy drinks are fine with your workout, as long as you don't stay over an hour which is overtraining anyway. Something like Speed Stack, Endorush, or Redline is good.
Just don't stay hooked on stimulants too long, as they can build up cortisol and lower your adrenaline levels over time. After about 8-9 weeks on stimulants, you should give yourself a good 7-8 weeks off of them to allow your natural adrenal glands time to recover. Use them strategicallty for fat loss instead of relying on them for daily energy,