Synthesis Of 1,8-Naphthalimide Derivatives And Their Application In Energy Transfer And PH Fluorescence Probes

Four 1,8-naphthalimide derivatives named N-butyl-4-(2′-amino ethyl)amino-1,8- naphthaimide (EBNT), N-butyl-4(-6′-aminohexyl)amino-1,8-naphthaimide (HBNT), THBNT and TEBNT containing four 1,8-naphthalimide fluorophores were synthesized. Their structures were characterized by FTIR, 1 H-NMR, MS and elementary analysis. The synthesis methods were modified and optimized and high yields were achieved.Photophysical characteristics of EBNT, HBNT, TEBNT and THBNT and their energy transfer with eosin were investigated: When the concentration of eosin was 2.5*10^-5 mol·L^-1, energy transfer between EBNT, HBNT, TEBNT and THBNT resulted in partial fluorescence quenching of eosin. The order of the contribution to quenching from low to high was THBNT>HBNT>TEBNT>EBNT. When the concentration of EBNT, HBNT, TEBNT and THBNT was fixed, the energy transfer efficiency rose with the concentration of eosin increased, and exceeded 90% at high concentration of eosin. HBNT, HBNT, TEBNT and THBNT could enhanced fluorescent intensity of eosin and offset it self-quenching at high concentration. The order of the contribution to enhancement from high to low was HBNT >TEBNT> THBNT>EBNT.The application of EBNT, HBNT, TEBNT and THBNT in pH fluorescence probes were studied: Between pH 1.82 and 12.36, their fluorescent intensity was greatly affected by pH values. The fluorescent intensity of EBNT and HBNT reduced with the increment of pH values. The fact that the fluorescent intensity of EBNT and HBNT changed linearly from pH8.71 to pH10.50 and pH6.51 to pH10.81 respectively indicated that EBNT and HBNT could be used as pH fluorescence probes. The fluorescent intensity of TEBNT and THBNT first increased with the increment of pH values and then decreased. Their fluorescent intensity increased abruptly from pH5.13 to pH5.48 and pH8.80 to pH9.15 respectively, and almost doubled. The mini-regions of the fluorescence mutation of TEBNT and THBNT reflected that they could be used as pH fluorescent switches.