There is nothing in the Constitution that ties the appointment of Electors to popular vote elections.
No for you
There is no direct tie, but the constitution establishes a Republican form of government. Fair elections are an inherent necessity in this form of government even if the Constitution does not specifically address them on this scale.
As Madison said of the constitution, "Had we undertaken the task of explaining every aspect, we would have written a digest of laws, and not a Constitution."