Air‐Stable Spirofluorene‐Containing Ladder‐Type Bis(alkynyl)borane Compounds with Readily Tunable Full Color Emission Properties

Abstract

A series of air-stable spiro-fused ladder-type boron(III) compounds has been designed, synthesized, and the electrochemistry and photophysical behavior have been characterized. By simply varying the substituents on the pyridine ring and extending the π-conjugation of the spiro framework, the emission color of these compounds can be easily fine-tuned spanning the visible spectrum from blue to red. All compounds exhibit a broad and structureless emission band across the entire visible region, assigned as an intramolecular charge-transfer transition originating from the thiophene of the spiro framework to the pyridine-borane moieties. In addition, these compounds demonstrate high photoluminescence quantum yields of up to 0.81 in dichloromethane solution and 0.86 in doped thin films. Some of the compounds have also been employed as emissive materials, in which solution-processed organic light-emitting devices (OLEDs) with tunable emission colors spanning the visible spectrum from blue, green to red have been realized, demonstrating the potential applications of these boron compounds in OLEDs.

Rigidly Fused Spiro‐Conjugated π‐Systems

“…Another series of rigid spiro-fused boron (III) compounds was designed and synthesized by Yam et al in 2016. [44] By varying the substituents on the pyridine ring and extending the π-conjugation of the spiro framework, the emission color of these compounds could be adjusted to span the visible spectrum from blue to red. These compounds demonstrated an increased PLQY of up to 81 % in CH 2 Cl 2 solution.…”

Recent Advances in π-Conjugated N^C-Chelate Organoboron Materials

“…OLED fabricated using 26 showed EL an emission maxima (λ max ) at 494 nm (i.e., intense green color) leading to 22.7% EQE with high current (56.4 Cd/A) and power efficiency (44.3 lm/W, Table 1). On the other hand, devices doped with spiro compounds 27a-c (Figure 12) exhibited tunable EL emission color [68]. Clearly, the presence of different N-donating substituents had a marked effect on the emission.…”

BN Embedded Polycyclic π-Conjugated Systems: Synthesis, Optoelectronic Properties, and Photovoltaic Applications

“…The reaction mechanism was proposed as follow: the Lewis acid-base coordination between 14 and BBr 3 provided 17 ; then, another BBr 3 captured a Br − from 17 , leading to trivalent cationic boron species 18 ; finally, the cationic boron attacked the neighboring aromatic unit, generating the circular 16 . After that, several conjugated units containing B←N coordination with tunable emission and aggregating-induced emission properties were synthesized by this method (Wong et al, 2012 , 2016 ; Zhao et al, 2013 ). Recently, based on this strategy, fused π-electronic units with good co-planarity, red-shifted absorption, and depressed energy levels of 21 , 23 , and 25 have been synthesized from 20 , 22 , and 24 , respectively (Yusuf et al, 2016 ; Zhu et al, 2016 ; Li Y. et al, 2018 ).…”