the selectionChanged.connect just doesn't trigger the get_Details any longer.
I don't think you understand how signals and slots work. A connection (via connect()) between a signal (selectionChanged()) amd a slot (get_Details()) does not result in an immediate function call to the slot code.

What a connect() means is this: "In the future, when this signal is emitted by the signalling object instance (selectionModel), call this slot (get_Details()) and pass that slot the arguments provided by the signal". (Which in this case are the QModelIndex indexes that have been selected and deselected).

You do not call connect() every time you want to retrieve the new selection and pass that to the slot. You generally call connect() once when you are creating the object instances you are connecting. Thereafter, you simply wait for your slot to be called whenever the signalling object changes state.

You haven't posted enough of your code to verify what you are actually doing, but your description of how you are invoking connect() makes it seem like you have a misunderstanding of the protocol.