Abstract:
1,8-diazafluoren-9-one (DFO) is one of the most common reagents used to enhance latent
fingermarks on porous substrates. However, this compound is slower to react than similar
reagents, and also does not always react to completion. This thesis investigated methods
to address these problems.
The reaction of DFO with fingermarks has been widely studied phenomenologically, but
there are few studies focusing on the chemistry of the reaction. Since the accepted
mechanism for the reaction of DFO with amino acids shows that DFO reacts in a 2: 1
stoichiometry with primary amino acids, linking two DFO moieties into one molecule
could provide the following advantages: First, the two DFO moieties are maintained in
close proximity thus increasing the chance that both can react with a single amino acid.
Second, fluorescence is dependent on the overall flexibility of the molecule, so a bridged
DFO dimer could lead to a more rigid product exhibiting greater fluorescence. Finally, a
cyclic product should be less susceptible to hydrolysis.
The synthetic route taken to synthesise DFO dimers involved five steps. The first step,
synthesis of the mono-N-oxide of DFO, proceeded cleanly and in good yields. The second
step involved the introduction of a halogen (chlorine and bromine) at the 2-position of the
N-oxide. The 2-chloro DFO was prepared cleanly and in good yields from the N-oxide,
while the 2-bromo derivative was prepared from the 2-chloro derivative via 2-amino
DFO. After protection of the carbonyl functional group (using acetals) the 2-halo DFO
intermediates were reacted with selected diols in basic conditions to form bridged dimers.
The final step involved deprotection of the acetal to give the carbonyl functional group.
Four bridged DFO dimers were synthesised. Crystal structures supporting two of these
compounds were obtained, while most of the intermediate compounds in the synthetic
route were characterised by NMR and mass spectrometry. Reaction of alanine with the dimer synthesised with a 2,2'-dimethyl-propane-1,3-diol
bridge leads to a colour change similar to that seen with DFO. This suggests that the
bridged analogues do react with amino acids and can therefore potentially be used as
alternatives to DFO. Characterisation of the product with L-alanine was difficult as mass
spectrometry indicated that it was polymeric. Attempted reactions at low concentrations
of both the dimer and the amino acid did not lead to the formation of the desired cyclic
product and in most instances, no reaction occurred. Attempts at metal ion templating
also were unsuccessful, possibly since metal ions can catalyse hydrolysis of the product
and intermediates during the reaction with amino acids.
The products obtained from the reaction of L-alanine with a series of 2-substituted
monomeric DFO compounds had similar absorbance and fluorescence spectra to the
unsubstituted product, although they showed decreased fluorescence intensity in solution.
Studies on porous substrates also indicated that none of the derivatives showed higher
fluorescence than DFO upon reaction with fingermarks. However, the halo- derivatives
appeared less susceptible to hydrolysis.
The imine of DFO is stable in ethanol: acetic acid and reacts about 10 times more rapidly
with L-alanine than does DFO at 60 oC and 78 oC, suggesting that the imine might allow
development of fingermarks at lower temperature than required for DFO. However, when
a fingermark on paper was treated with DFO and DFO imine, the DFO imine treated
fingermark did not show significantly more colour or fluorescence than that with DFO
treatment.