Color-Tunable Fluorescence And White Light Emission From Mesoporous Organosilicas Based On Energy Transfer From 1,8-Naphthalimide Hosts To Perylenediimide Guests

The present work reports Forster resonance energy transfer (FRET) from 1,8-naphthalimide (NI) donors bound to the pore walls of mesoporous silicas to perylenediimide (PDI) acceptors doped into the mesochannels. Mesoporous organosilicas containing covalently bound NI were synthesized by co-condensation of tetraethylorthosilicate (TEOS) with N-(3-(triethoxysilyl)propy1)-1,8-naphthalimide (TEPNI) in the presence of a block copolymer surfactant as a template. The resulting materials were highly ordered, presenting a 2D hexagonal structure, and displayed easily tunable optical properties, which could be controlled by the amount of NI in the sample. A sample prepared from a diluted TEPNI solution (SBANId) presented a blue, monomer-like emission. In contrast, when a concentrated TEPNI solution was used, the resulting material (SBANIc) displayed a green, excimer-like emission. For the FRET studies, N,N'- bis(2,6-dimethylpheny1)-3,4,9,10-perylenediimide was doped into the pores of the SBANI samples from chloroform solutions. When excited at the NI absorption maximum (350 nm), PDI-doped SBANIc showed intense quenching of the NI emission band, even at very low PDI doping, with quenching efficiencies reaching nearly 80% with only 0.6 mol % PDI (PDI/NI approximate to 1:170). The emission of PDI was observed at higher doping ratios, even though the PDI hardly absorbs at 350 nm, thus evidencing FRET from the host NI to the guest PDI. SBANI materials with a suitable amount of the PDI dopant displayed a white emission, spanning the whole visible spectrum.