Jefferson was in Paris as Ambassador from August 1784 to September 1789 and wasn’t in the United States for the Constitutional Convention, which took place in 1787.
The Convention was the third of a series convened to solve issues between the states, beginning with the Mount Vernon Conference convened over a proposal to build a canal along the Potomac.
The Philadelphia Convention was called to revise The Articles of Confederation, but Madison and Edmund Randolph instead suggested the Virginia Plan which served as the basis of the Constitution. Washington presided over the convention. Hamilton was a delegate from New York.
John Adams, like Jefferson, did not participate in the Convention although both had been on the list of 70 men invited. Patrick Henry, Richard Henry Lee, John Hancock, Sam Adams likewise didn’t show.