Negative Lookahead Equivalent in emacs

[luishenriquezperez@gmail.com]

Hi,

I'm trying to write a regex that matches the last character of a sequence of non-whitespace characters '[^\n\r\t\f ]', or an empty line matching ^$. 

Thus: 
Hello World! --> "o" and "!" would be matched

In non-elisp regex languages I know the code for this is: \S(?!\S) 
I know that \S is equivalent too [^ /n/r/t/f]. 
But I'm unsure of what the elisp equivalent (if any) of the negative lookahead (?!).

I saw on this forum a post  "gnu.emacs.help › regex nirvana - near miss"
Where Drew Adams said: "Typically, what you want to do for this in Emacs Lisp is to combine 
the use of a regexp for positive matching with other code that takes 
care of the non-matching (negation) need. "

However, I'm not sure how to go about doing this.