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; At = -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(g)s in the range of 85-147 degreesC and displayed high thermal stabilities with T(d)s in the range of 329-385 degreesC. Compounds 5-8 exhibited strong absorptions in solution with lambda(max) at 318-326 nm and log c 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.