New 8-NR2-BODIPYs, R2 = H(i)Pr (3a), H(i)Bu (3b), and Et2 (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)nOH, n = 1-6. In mixed-solvent 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 parent 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 π system due to the steric impact of the two ethyl groups, an observation that explains the lack of emission for 4.

Fluorescent members of the 4, 4‐difluoro‐4‐bora‐3a, 4a‐diaza‐s‐indacene (BODIPY) family are widely used for a range of markers, dyes, and sensors. The capacity to substitute the basic framework is an attractive feature permitting a range of differently substituted materials to be formed. New isomeric BODIPYs, o‐, m‐, and p‐8‐[R‐C6H4]‐BODIPY (R = CH2OH, 2a (o), 2b (m), 2c (p); R = OMe, 3a (o), 3b (m), 3c (p)), have been synthesized and characterized by nuclear magnetic resonance, absorbance and emission spectroscopy, and single crystal X‐ray diffraction. The o‐isomers have a very high quantum yield emission in non‐polar solvents, while the m‐ and p‐ analogs showed weak fluorescence under the same conditions. Spectroscopic analysis, as well as X‐ray structural characterization, suggested that substitution in the ortho‐position of the phenyl ring is sufficient to increase the steric hindrance and hence impede the rotation of the phenyl moiety about the 8C‐C axis, thereby favoring radiative compared to non‐radiative relaxation. Copyright © 2013 John Wiley & Sons, Ltd.

The simple reaction of phenylthiol with 8-MeS-BODIPY (1) in dichloromethane was readily accomplished to form 8-PhS-BODIPY (2). If the reaction is performed in THF 3,8-bis(phenylthio)-BODIPY (3) and 3,5,8-tris(phenylthio)-BODIPY (4) are sequentially formed in an unprecedented reaction. This provides a simple new methodology for the introduction of the phenylthio-moiety in the 3- and 5-positions. Alkyl thiols do not form multi-thiolated products under identical conditions, as exemplified using EtSH, where only 8-EtS-BODIPY (5) is formed.

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Reactions between 8-RS-BODIPY (R = Me, 1) and alkyl and aryl thiols were readily accomplished in dichloromethane (DCM) to provide a synthetic pathway to a range of new 8-organothioBODIPYs in good yield. The new alkyl 8-RS-BODIPYs, R = Et, 2; Pr, 3; Bu, 4; t Bu, 5, n-Dodecyl, 6; exhibit absorption and emission properties essentially unchanged from those of 1 whereas the arylthio analogs, R = Ph, 7; 2,6-Me 2 C 6 H 3 , 8; p-MeC 6 H 4 , 9; p-MeOC 6 H 4 , 10, exhibit no fluorescence with the exception of 7, and then only in hexane. In common with other related 8-substituted BODIPYs the new 8-alkylthio-BODIPY dyes show decreasing fluorescence intensity as solvent polarity increases. Compounds 2, 3, 7, and 8 were characterized via single crystal X-ray analysis; the alkyl derivatives 2 and 3 exhibited planar BODIPY cores with co-planar organothio-substituents, whereas the aryl derivatives exhibited both BODIPY core deformation and significant twisting about the S-C(8) bond removing co-planarity between the aryl group and the distorted BODIPY core.These deformations coincide with the significantly reduced emission properties.