Fluorene derivatives with intramolecular charge-transfer: exceptionally easy rotation around the double C(9)C(α) bond in nitro-substituted 9-aminomethylenefluorenes

Abstract

Strong intramolecular charge-transfer which occurs in fluorenes 2 and 3 from the donor amino group(s) to the acceptor fluorene moiety leading to exceptionally easy rotation around the C(9)C(α) bond has been observed in solution by ¹H NMR and UV–VIS spectroscopy; single crystal X-ray analysis of compound 2h shows significant π-bond delocalization along the C(9)–C(14)–N(2) fragment.