The current generation of Samsung Frames can be reliably controlled using CEC, but your CEC source needs to be "unregistered". I suggest using the following:
Power on - \xF0\x04
Power off - \xF0\x36
However, on the latest generation of Samsung Frame, art mode should be considered the standard off state. The only way to get the TV into a "full off" state is a press and hold from the IR remote control.
If the TVs are in spaces where they need to be dark like bedrooms, then you will need to use the Samsung art settings to adjust when art is shown. There are settings for motion detection, ambient light level and if memory serves, time ranges as well.
Regards,
Bruce
Bruce Bartlett