PhD ThesisBoron dipyrromethenes (BODIPYs) have attracted considerable attention due to their
fluorescence properties, including high fluorescence quantum yields and absorption
coefficients, good photochemical stability and narrow absorption and emission
bandwidths. Because of these properties, they have found extensive use for in vivo
imaging, analyte sensing, photodynamic therapy, solar cells and light harvesting arrays.
This thesis is divided in two parts. Part one covers the synthesis of functionalised chiral
BODIPYs whilst part two involves investigations into the synthesis and application of
aminoBODIPY via metal catalysed amination reactions.
Four approaches to the synthesis of novel chiral BODIPY dyes were investigated. The
axially chiral BODIPY dye with C2-symmetry I was synthesised via Suzuki coupling of
the corresponding 2,6-dibromoBODIPY with 2-methoxyphenyl boronic acid. The
unsymmetrical axially chiral BODIPY II was synthesized via Suzuki coupling of the
corresponding 2-bromoBODIPY with phenyl boronic acid. Unfortunately, attempted
resolution of these chiral systems by analytical chiral HPLC was unsuccessful.
The new helically chiral BODIPYs IIIa-c were synthesised. Resolution of racemic
helically chiral BODIPYs IIIa and IIIb was successfully accomplished by preparative
chiral HPLC.
Abstract
ii
Electronic circular dichroism (ECD) spectra of both (M) and (P) isomers of IIIa and IIIb
were measured by Prof. W. Herrebout (University of Antwerp). Comparison of the
measured and computationally predicted ECD spectra allowed the absolute configuration
of each of the enantiomeric samples of IIIa-b to be established. The CPL spectra of both
(M) and (P) isomers of IIIa and IIIb were recorded by Prof. R. D. Peacock (University
of Glasgow). The |glum| of IIIa at 637 nm is 0.0043 and IIIb at 675 nm is 0.0042, which
are among the largest so far reported for a simple BODIPY fluorophore in solution.
We designed and synthesized the mono-strapped BODIPY V scaffold via sequential
regioselective functionalisation of the unsymmetrical BODIPY IV. Resolution of
N,N,F,O-BODIPY V by analytical chiral HPLC gave two peaks confirming that single
enantiomers of this compound should be accessible.
The 8-anisyl-substituted BODIPY VI was synthesized using a standard synthetic route,
regioselective iodination with ICl then gave the 2-iodo-substituted BODIPY VII. We
unexpectedly found that copper catalysed nucleophilic substitution of the 2-iodoBODIPY
VII produced the 3-amino BODIPYs VIIIa-n in good yield. The reactions occurred
successfully for a range of primary and secondary alkyl and aryl amines and even with
benzamide, albeit in low yield.
2-aminoBODIPYs Xa-e have been prepared successfully via Buchwald–Hartwig
amination of the 2-iodoBODIPY IX (fully blocked). The presence of the nitrogen group
Abstract
iii
in the 2-position gives a broadened red-shifted absorption maximum and quenched
fluorescence.
This palladium catalysed amination was used to prepare the 2-nitroaniline-substituted
BODIPY XI. Reduction of the nitro group by hydrogenation gave the novel fluorescencequenched
2-aminoaniline-substituted BODIPY XII. Reaction of this compound with
triphosgene gave the corresponding benzimidazolone-substituted BODIPY XIII. The
bright yellow fluorescence of the triphosgene reaction product XIII can be easily
visualized by the naked eye. The detection limit for phosgene was determined to be 160
nM in solution at room temperature.Taibah Universit