8-Amino-BODIPYs: Structural Variation, Solvent-Dependent Emission, and VT NMR Spectroscopic Properties of 8-R<sub>2</sub>N-BODIPY
作者:Robinson I. Roacho、Alejandro Metta-Magaña、Michelle M. Portillo、Eduardo Peña-Cabrera、Keith H. Pannell
DOI:10.1021/jo302758a
日期:2013.5.3
New 8-NR2-BODIPYs, R-2 = (HPr)-Pr-i (3a) (HBu)-Bu-i (3b), and Et-2 (4), are reported. Restricted rotation about the C8-N bond in such molecules has been observed for the first time (3a and 3b) and evaluated using VT NMR. The fluorophores 3a and 3b are blue emitters, and the efficiency of the emission is closely related to the polarity of the solvent, e.g., hexane > toluene > DCM > THF > MeOH > H2O, an effect also noted by emission variation in alcohol solvents H(CH2)(n)OH, n = 1-6. In mixed-solvents systems, addition of 10-15% of the more polar solvent results in transformation of the emission properties to those of the bulk polar solvent. Compound 4 has zero emission in all solvents. The crystal structures of 3a, 3b and 4 are reported, along with that of the present 8-NH2-BODIPY (2). Compounds 2, 3a, and 3b exhibit trigonal planar N atoms which are coplanar with the BODIPY core; 4 exhibits a very significant distortion that breaks the planarity of the extended BODIPY pi system due to the steric impact of the two ethyl groups, and observation that explains the lack of emission for 4.