Highly Efficient Blue-Light-Emitting Glass-Forming Molecules Based on Tetraarylmethane/Silane and Fluorene:  Synthesis and Thermal, Optical, and Electrochemical Properties

The paper reports the first blue-light-emitting tetrahedral glass-forming molecules derived from fluorene and several tetrahedral core compounds. The glass-forming molecules (5 − 8) were prepared from three tetrabromo cores of X(p-ArBr)4 (X = C, Si; Ar = -C6H4-, -C6H4C6H4-) and an octabromo core of tetra(2,4-dibromobiphenyl-4‘-yl)methane with 9,9-dihexylfluorene-2-MgBr via Grignard coupling reactions. Compounds 5 − 8 exhibited obvious glass transition behaviors with T gs in the range of 85−147 °C and displayed high thermal stabilities with T ds in the range of 329−385 °C. Compounds 5 − 8 exhibited strong absorptions in solution with λmax at 318−326 nm and log ε at 5.95−6.28. The emission maxima of these compounds in THF were in the range of 377−405 nm with high PL quantum yields of 79−100%. Under UV light excitation, their spin-coated films emitted intense blue-light peaking at 405−415 nm with quantum yields of 25−98%. The films emitted relatively pure blue light with small fwhm (full width at half-maximum) values of 57−75 nm and absences of excimer-like long wavelength emissions, due to the nonaggregating property of the tetrahedral compounds in the solid state. The two Si-centered molecules exhibited better film-forming property and much higher film PL quantum efficiencies than their C-centered counterparts. The present tetrahedral molecules would represent a novel class of nonaggregating blue-light-emitting molecular glass-forming materials based on the fluorene fluorophore that were easily synthesized by a one-step Grignard coupling reaction.