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43041-B4
Synthesis, Metal Ion Complexation, and Emission Studies of Naphthalimide Based Fluoroionophores

Jeffrey E. Elbert, University of Northern Iowa

During this reporting period, we continued studies toward the synthesis of secondary amino substituted butyl naphthalimide (Figure 1).  The reaction of secondary amines with halonaphthalimides has proven difficult, presumably due to the increased steric hindrance of the naphthalene moiety as compared to similar benzene systems.  Several solvent systems have been studied, including ionic liquids, in an effort to increase solubility of the reagents and increase the reaction temperature.  To date, we have NMR and LCMS evidence of 2°-DETA and are working to increase reaction yield in order to completely purify and characterize the product.  In the next year, we plan to complete photochemical and photophysical studies of 2°-DETA in the presence of trace metal ions and compare the results with those obtained for 1°-DETA (Figure 2).

 Figure 1. 2°-DETA                  Figure 2. 1°-DETA

            Completion of our studies of 1°-DETA and the observation that addition of chain length and nitrogens to the ligand system does not increase metal ion selectivity or fluorescence enhancement prompted us to examine the effect of alkyl substitution on the distal amine (Figure 3).  4-N',N'-Dimethylethylenediamine (DMED4), 4-N',N'-diethylethylenediamine (DEED4), and 4-N'-methylethylenediamine (MMED4) substituted butyl naphthalimides were synthesized.  Results of fluorescence enhancement studies of DMED4 and DEED4 were similar to results obtained with 4-butanediamine (BD4) substituted butyl naphthalimide.  Greater fluorescence enhancement than for the ethylenediamine (ED4) or propylenediamine (PD4) derivatives was recorded, but less shifting of the long wavelength emission to the blue is observed.  Selectivity for larger metal ions such as Pb²⁺ is also observed for DMED4 and DEED4 as compared to smaller metal ions such as Cu²⁺ for ED4 and PD4.  In this respect DMED4 and DEED 4 also behave similarly to BD4.

Figure 3.  4-Alkyl substituted butyl naphthalimides

We are continuing our studies of the synthesis of naphthalimides with the polyamine in the imide position (figure 4).  Coupling products of two naphthalimides through the polyamine linker have been the major product of our initial trials.  Boc-protected diethylenetriamine has lead to the desired major product by LCMS, but isolation after deprotection has been problematic.  Boc-protected ethylenediamine has also resulted in good yields prior to deprotection, but isolation difficulties of the unprotected product.  Diethyldiethylenetriamine derivatized naphthalimide is our target for the next year.  This derivative will yield the desired product without requiring deprotection.  Comparison of the results of fluorescence enhancement studies will be compared with 1°-DETA and DEED4.

Figure 4. Diethylenetriamine imide product.

Photodegradation studies of 44 (Figure 5) are progressing.  We have conducted the reactions in buffered water at pH's of 4, 7, and 10, under N₂ bubbling, irradiating with a Rayonet reactor equipped with lamps centered at 420 nm to excite into the charge-transfer band of 44.  Plotting the results of different irradiation times monitored by GCMS clearly shows a product growing in with time whose mass matches 4-amino butylnaphthalimide (Figure 6).  The product grows in fastest at low pH and no reaction is observed at high pH.  The reaction stops at low pH after approximately an hour.  Irradiation of solution buffered to pH 7 shows product growing in for at least 4 hours, our current time limit.  Irradiation of air saturated solution results in reactant degradation with no photoproducts observed.  Presumably the solutions are photooxidizing. The pH dependence of the photoreaction will be examined in more detail, as this is an important key to the mechanism of this reaction.

Figure 5.  4-Butylaminobutylnaphthalimide (44)

Figure 6. Photolysis results of 44

                During this reporting period, four students were directly supported by grant funds and three students were indirectly supported through materials purchased by grant funds.  These students experienced research activities and worked with equipment most undergraduate students do not have access to allowing them to greatly advance in their studies toward becoming independent chemists, which will greatly aid them in their future endeavors.  The undergraduate students working with me this reporting period are all graduate school bound, so research is a necessary activity to prepare them for their next phase of training.  The research project funded during this reporting period has allowed me to continue my personal study in chemistry and photochemistry.  Research activities are the primary means for academic chemists to remain current in the field.  Excitement for chemistry is definitely noticed by students at all levels, not just during research.

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