Villas-Boas was officially unveiled this morning and will earn around £15million over the course of his three-year contract.
But the 33-year-old denied money was a motivating factor behind his move back to west London.
He said: "I can assure you that Porto could beat that offer. They were ready to make a competitive offer for me to stay, but I took the challenge.
"I've made some very difficult moves in my life. One of them was leaving a crazy salary at Inter Milan as an assistant to join the bottom club in Portugal (Academica).
"So I just felt it inside me that I should take the opportunity and the move.
"Against the will of everybody, against the will of my family, I took that."
Explaining their concerns, he said: "We have spent seven years moving around from London to Milan to Coimbra to Porto and now to London.
"This causes an emotional instability in any family."