Você não pode usar uma tecla de função, porque isso envia vários caracteres. De acordo com o manual:
escapexySet the command character to x and the character generating a literal command character (by triggering the "meta" command) to y (similar to the -e option). Each argument is either a single character, a two-character sequence of the form
"^x"(meaning"C-x"), a backslash followed by an octal number (specifying the ASCII code of the character), or a backslash followed by a second character, such as"\^"or"\". The default is"^Aa".
Cada formulário, no entanto expresso, corresponde a um único código ASCII.