Ln3+-enhanced blue fluorescence from novel excimer of 1,8-naphthalimide-conjugated PAMAM

Abstract In this article, the 1,8-naphthalimide-conjugated polyamidoamine (PAMAM) [D n ( n = 3, 4, and 5)] was synthesized by the modification reaction of PAMAM with 1,8-naphthalimide (1,8-NI). The results show that the 1,8-NI groups around the periphery of PAMAM emit strong blue fluorescence at 476 nm and this emission can be enhanced by Ln 3+ ions (e.g., La 3+ , Eu 3+ , and Tb 3+ ). Compared with the emission of 1,8-NI solution at 386 nm, the enhanced fluorescence at 476 nm by Ln 3+ ions in D n was emitted from the excimer of 1,8-NI groups around the periphery of PAMAM dendrimer. In this system, Ln 3+ ions were not emission centers via f – f transitions in organic lanthanide complexes yet, whereas they are the efficient inhibitors of photo-induced electron transfer (PET) between 1,8-NI and nitrogen atoms in PAMAM skeleton. Among used Ln 3+ species, La 3+ has the strongest enhancement effect. The characteristic emission bands for Eu 3+ and Tb 3+ were not found in this study. As comparison, all the transition metals, such as Fe 3+ , Co 2+ , Cu 2+ , and Zn 2+ , showed the quenching effect on 1,8-NI excimer emission. This novel blue fluorescence material will be expected for the potential application for excellent basic color polymeric material.