High Pseduo-Stoke's Shift of a Naphthalene-Bisindolylmaleimide Dye.

An energy transfer cassette was reported with energy donor and acceptor incorporated in one molecular. The two units (naphthalene and bisindolylmaleimide) were connected by covalent single bond. The intramolecular repulsion twisted the molecular conformation, thereby forcing the two units act as independent chromophores. Upon photoexcitation (λ = 280 nm), bright emission peak was observed around 583 nm. The intramolecular cascade energy transfer from the naphthalene moiety to the bisindolylmaleimide framework is efficient and the efficiency is estimated to be 86%, providing large pseudo-Stoke's shift (303 nm). At such a short separation, the orbital overlap interaction was completely isolated between chromophoric units. Computational study was carried out based on DFT. Further analysis of optimized structure and FMOs supports the efficient energy transfer in NBM. Favorable photophysical properties, such as efficient energy transfer, strong emission, and large Stoke's shift make it an attractive functional dye.