Pity the offspring of Johann Sebastian Bach: Lavishly gifted as musicians, they’ve never been able to escape the vast shadow of their father. That’s certainly the case of second son Carl Philipp Emanuel Bach, who broke from the formal musical herd of the time to develop a distinctive and highly influential “Empfindsamer” (or “sentimental”) style, full of sudden shifts in rhythm and harmony, overheated emotionalism and a kind of quirky, almost operatic drama. It’s fascinating stuff but not widely heard anymore, so it was a treat to hear soprano Julianne Baird, with Preethi de Silva on harpsichord and pianoforte, offer up a program on Friday night at the Library of Congress that made a strong case for a revival of this intriguing composer.