You mean the longest notation? We discussed this a while back and yes, the pawn capture-promotion-check is one of the longest pieces of shorthand notation possible, with 7 characters. It is tied with Nd1xc3+
The longest geometric move would be Ba1-h8. The longest chronologic move would be the one right before mate, by a sore loser.

A move is something like f4 or Ng5. What's the longest one you can think of? I though of: fxg8=Q#.