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

Abstract

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 ) -C 6 H 4 -, -C 6 H 4 C 6 H 4 -) 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 °C and displayed high thermal stabilities with T d s in the range of 329-385 °C. Compounds 5-8 exhibited strong absorptions in solution with λ max at 318-326 nm and log 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 halfmaximum) 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 bluelight-emitting molecular glass-forming materials based on the fluorene fluorophore that were easily synthesized by a one-step Grignard coupling reaction.

Excimer and electromer suppression of tetraphenylsilane‐based blue‐light‐emitting polymers

“…[13][14][15][16] Recently, a series of tetraphenylsilane-based hyperbranched blue-light-emitting alkylfluorene copolymers were developed by He and coworkers. [17][18][19] No excimer formation in longer wavelength like emissions at 500-600 nm was observed for such hyperbranched PFs. The color purity of blue emissions was shown to be improved by the reduction of the aggregates formed by polymer-chain p-p stacking in the solid state of PFs.…”

“…However, the presence of the tetrahedral molecular skeleton of tetraphenylsilane groups or the hyperbranched structure effect on the reduced aggregation and excimer formation of PF were not clarified. [17][18][19] More recently, a comparative study on light-emitting copolymers of fluorene and carbazole with a full conjugated or Si-interrupted structure was carried out by He et al 20 The results seem to conclude that the self-aggregation of PF could be significantly reduced because of the steric effect of the tetrahedral molecular skeleton of teterphenylsilane groups. In fact, the maximum and full width at half-maximum (fwhm) of the emissions were not reduced as the conjugated structure was interrupted by the teterphenylsilane group.…”

Synthesis, electroluminescence, and photovoltaic cells of new vinylene‐copolymers with 4‐(anthracene‐10‐yl)‐2,6‐diphenylpyridine segments

“…For organic solar cells, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was blended with the synthesized copolymer (1 : 1 in wt/wt ratio), dissolved in chlorobenzene, and cast into thin film by spincoating. In this case TPBI was left out.…”

“…6 Fluorene and/or anthracene-based compounds, in particular, are often used as emitting materials in electroluminescent (EL) devices. [7][8][9][10][11][12][13][14][15][16] On the basis of the previous reports, promising low molecular weight emitter for use in LEDs should have an appropriate HOMO/ LUMO band gap as compared with those of the electron-and hole-transporting materials, high PL quantum yield (U f ), good film-forming properties, and durability to heat during the vacuum deposition.…”

Efficient and bright non-doped blue light-emitting diodes based on glassy styrylcarbazoles

“…In the tetrahedral tetraphenylsilyl core, the δ-C/Si atoms effectively interrupt the regular π-conjugation system. The tetraphenylsilane prevents the red-shift of blue emission associated with the increase in conjugation length [46][47][48][49][50][51].…”