Dioscorus Boles has written an excellent article on one of the Coptic Fathers: An aid to the study of St. Pisentios, bishop of Coptos: his life and two famous letters. Even the most detailed patrologies give little information about this 7th century Father, but his life and letters are important among the Coptic Fathers.
Dioscorus has linked to the primary sources, in several languages, and English and French translations. The first letter is an exhortation to his flock not to convert to Islam; the second belongs to Coptic apocalyptic literature.
Very useful – thank you!