Emission and energy transfer investigation of non-conjugated total carbon configuration between BODIPY and naphthalimide.

An energy cassette, N-butyl-6-(3-phenylethynyl-1,3,7,9-tetramethylBODIPY)-naphthalimide (BON), was constructed with an energy donor and acceptor incorporated in a single molecular system. The energy donor (naphthalimide, NA) and acceptor (BODIPY) were bonded through phenylacetylene, a conjugate linker. Highly twisted molecular conformation was formed due to intramolecular repulsion, forcing the two fluorophores to act as independent chromophores. Therefore, the absorption spectra of BON in a common organic solvent are of superimposition of NA and BODIPY. Upon excitation of UV light (365 nm), a typical BODIPY emission character was observed, indicating an efficient energy transfer from NA moiety to the BODIPY scaffold with a transfer efficiency of 98%. Additionally, the pseudo-Stokes' shift expanded to around 140 nm, which is largely longer than traditional BODIPY dyes (~ 10 nm). The frontier molecular orbitals analysis shows that there exists a pronounced electron density shifting from HOMO to LUMO, suggesting the efficient energy transfer in BON. A through-space energy transfer cassette was established with the twisted molecular conformation-induced orbital decoupling and favorable mutual orientation of the excited NA/BODIPY moment vector. A dye pair (BON) was configured by naphthalimide and BOIDPY with a conjugate linker, phenylacetylene. Due to intramolecular repulsion in BON, the dye molecule is highly twisted, forming an efficient energy transfer cassette. An efficient energy transfer from NA to BODIPY occurred with a transfer efficiency of 98%. [ABSTRACT FROM AUTHOR]