A series of mono-, di-, and triphosphoniumsubstituted triarylboranes, [Mes 2 BAr P ]I ([2]I), [MesBAr P 2 ]I 2 ([3]I 2 ), and [BAr P 3 ]I 3 ([4]I 3 ) (Ar P = 4-(MePh 2 P)-2,6-Me 2 -C 6 H 2 ), were prepared from the corresponding neutral boranes 2a−4a. The crystal structure of [4]I 3 determined by X-ray diffraction study reveals peripheral decoration of aryl groups with phosphonium moieties. The anion affinity of the cationic boranes for fluoride and cyanide ions was investigated by UV−vis absorption titrations in aqueous solution. The triarylboranes, [2]I−[4]I 3 bind both fluoride and cyanide ions in a DMSO/H 2 O (7:3 v/v) mixture with high binding constants (K). Comparison of the K values of triarylboranes for fluoride reveals that fluorophilicity increases with the increasing number of phosphonium moieties: [2] + (K = 2.3 × 10 1 M −1 ) < [3] 2+ (3.6 × 10 5 M −1 ) < [4] 3+ (1.0 × 10 7 M −1 ). A similar trend is also observed in the cyanide binding, with K values that are greater by 2−4 orders of magnitude than those in the fluoride binding. These results indicate an apparent additive effect of multiple phosphonium substitutions on the Lewis acidity enhancement of triarylboranes. The triphosphonium borane [4]Cl 3 , a water-soluble form of [4]I 3 , was further utilized in evaluating the anion affinity in water. While [4] 3+ is shown to hardly bind fluoride in buffered water at pH 7, it binds cyanide with a high binding constant (1.7 × 10 7 M −1 ).

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Compared favorably with conventional field emitters made of metal such as molybdenum, CNTs have superiority of field enhancement due to high aspect ratio and durability of emitters due to high thermal conductivity and chemical inertness. Briefly research to fabricate field emitters using CNTs consists of direct-growth and indirect-attachment.Because of vertical alignment and high adhesion force, emitters fabricated by direct-growth generally show better properties of field emission than those fabricated by indirect-attachment. In contrast, indirect-attachment have little constraint of substrate and requires simple and short process relatively.Indirect-attachment methods are compatible with industrialization due to short process time and possibility of application to large substrate. Therefore CNT paste method of indirect-attachment have been investigated intensively [1]. CNT paste method is to spread paste, consisted of CNTs, binders and solvent, over a substrate and make CNTs attached and vertically-aligned by taping method in order to activate CNTs for field emitters. However, taping method can not avoid inevitable secondary contaminations ,which degrade properties of field emission during activation process of CNTs.Our research suggests that triboelectricity method is more compatible with fabrication of field emitters using indirect-attachment than conventional taping method. CNTs are attached on silicon substrate with dip-coating method. In order to reduce loss of CNTs and induce frictional electricity between interfaces, thin insulating film such as plastic cooking wrap is covered over the substrate and is rubbed with cotton. After frictional electricity is induced enough, insulating film is removed to activate CNTs (See Fig. 1). Triboelectricity method is able to avoid secondary contaminations due to residues of adhesives because it does not use any adhesive.In order to confirm existence of frictional electricity, surface potential is measured at 1 cm above the specimens with electrostatic voltimeter (model 344, Trek Inc). The electrostatic voltimeter is induction probe type with 2 mV resolution. Right after specimens are treated with triboelecticity method on bulk insulator, surface potential is measured to minimize measuring error (See Fig. 2).Properties of field emission is measured with diode type (0.2827 cm 2 emission area, 610 µm cathode-anode gap, 3 × 10 -6 torr high-vacuum). As shown in Figure 3, properties of field emission with respect to emission current are enhanced from non activation (0 µA, dot line) to activation (270 µA, solid line) under 4 V/µm of electric field.