Abstract:
1,8-diazafluoren-9-one (DFO) reacts with α-amino acids to form the fluorescent product 9- (1,8-diazafluoren-9-ylidene)amino-1,8-diazafluorenone (DFYADF). DFYADF is a pale pinkpurple in colour and produces an intense yellow-orange fluorescence when illuminated with light over a wide spectral range between 450 nm and 560 nm. Within a cellulose matrix such as paper or untreated wood, DFO reacts selectively with the amino acids present in fingermark deposits. Minimal staining of the substrate is observed so under optimal conditions, fingermark ridge patterns are revealed with the highest levels of contrast on highly patterned or coloured backgrounds. For these reasons, DFO is widely used for fluorescence imaging of latent fingermarks on porous surfaces. An issue with DFO is its poor solubility in the HFE-7100 carrier solvent. This has been partially overcome by optimisation of solvent formulations, in particular by employing small proportions of polar co-solvents in order to achieve dissolution of the reagent and inhibit precipitation during storage. However, there exists a fine balance between the maximum DFO concentration attainable without precipitation and an acceptable co-solvent load above which diffusion of inks will occur. In this research, DFO derivatives were synthesised which exhibit greater solubility in fluorinated carrier solvents. Synthesis of the target compound 2-(1'H,1'H,2'H,2'Hperfluorooctyloxy) DFO was achieved in six steps. DFO was activated toward nucleophilic substitution of chlorine at the 2-position by N-oxidation, giving the mono N-oxide of DFO. The 2-chloro derivative was obtained by stirring DFO mono N-oxide in POCl3, and the reactive ketone group was subsequently protected by conversion to the dimethyl acetal. Attempts at directly coupling the commercially available fluorinated alcohol 1H,1H,2H,2Hperfluoro- 1-octanol with 2-chloro DFO dimethyl acetal by refluxing both compounds in a suspension of NaH failed. However, a low yield of an HF elimination product 2- (1'H,1'H,2'H,2'H,4'H,4'H,5'H-3-oxaperfluoroundec-5'-eneoxy) DFO was achieved by substitution of the Cl in 2-chloro DFO dimethyl acetal with a short 2-hydroxyethoxy extension and then refluxing the resulting product with the tosylate of 1H,1H,2H,2Hperfluoro- 1-octanol in a suspension of NaH and the phase transfer catalyst 15-crown-5. Synthesis of 2-hydroxy DFO dimethyl acetal followed by coupling with 1H,1H,2H,2Hperfluoro- 1-octanol via a Mitsunobu reaction using diisopropyl azodicarboxylate (DIAD) as the proton acceptor gave a fluorinated DFO dimethyl acetal. Deprotection of this 2- (1'H,1'H,2'H,2'H-perfluorooctyloxy) DFO dimethyl acetal gave the desired product 2- (1'H,1'H,2'H,2'H-perfluorooctyloxy) DFO. In preliminary fluorescence testing 2-(1'H,1'H,2'H,2'H,4'H,4'H,5'H-3-oxaperfluoroundec-5'- eneoxy) DFO was found to develop latent fingermarks of similar brightness and clarity when compared to DFO in the standard solvent formulation. 2-(1'H,1'H,2'H,2'Hperfluorooctyloxy) DFO did not prove to be useful as a reagent for developing latent prints on paper, producing no observable fluorescence.