Substituent Modulation for Highly Bright 9-Borafluorene Derivatives with Carbazole Pendant.

A series of 3,6-di-tert-butyl carbazole-functionalized 9-borafluorene derivatives have been prepared with outstandingly strong photoluminescence with quantum yields up to ca. 100 and 94% for Mes*BF-pCz in solution and film, respectively. 1,3,5-Tris(trifluoromethyl)benzene (FMes)-substituted compounds exhibit enhanced Lewis acidity with coordination to weak nucleophiles like tetrahydrofuran, resulting in a long afterglow at low temperature. The large two-photon absorption cross-section of ca. 1103 GM for Mes*BF-pCz at 800 nm in CH2Cl2 indicated its potential application in bioimaging.