Anions often quench fluorescence (FL). However, strong ionic hydrogen bonding between fluorescent dyes and anion molecules has the potential to control the electronic state of FL dyes, creating new functions via non-covalent interactions. Here, we propose an approach, utilising ionic hydrogen bonding between urea groups and anions, to control the electronic states of fluorophores and develop an aggregation-induced emission enhancement (AIEE) system. The AIEE ionic hydrogen-bonded complex (IHBC) formed between 1,8-diphenylnaphthalene (p-2Urea), with aryl urea groups at the para-positions on the peri-phenyl rings, and acetate ions exhibits high environmental sensitivities in solution phases, and the FL quantum yield (QY) in ion-pair assemblies of the IHBC and tetrabutylammonium cations is more than five times higher than that of the IHBC in solution. Our versatile and simple approach for the design of AIEE dye facilitates the future development of environment-sensitive probes and solid-state emitting materials.
A triruthenium hydrido
complex in which one of the Ru3 planes is capped by a μ3-BO ligand, [{Cp*Ru(μ-H)}3(μ3-BO)(μ3-H)] (3; Cp* = η5-C5Me5), was synthesized
by the reaction of the μ3-borylene complex [{Cp*Ru(μ-H)}3(μ3-BH)] (2a) with water in
the presence of Et2NH. The face-capping coordination of
the oxoboryl ligand was unambiguously established by X-ray diffraction
and exhibited short B–O (1.231(6) Å) and long Ru–B
bonds (average 2.31 Å). Density functional theory (DFT) calculations
of 3 reproduced the observed structure well, and the
multiplicity of the BO bond suggested by the value of the Wiberg bond
index is 1.62. The four hydrido ligands in 3, three μ-hydrides
and one μ3-hydride, underwent site exchange on the
NMR time scale via the formation of a μ3-hydroxyborylene
intermediate, [{Cp*Ru(μ-H)}3(μ3-BOH)]
(2c). The DFT calculations showed that 2c lies above 3 by 10.5 kcal mol–1 at
25 °C. The basic oxygen atom in 3 allowed the formation
of a B(C6F5)3 adduct, [{Cp*Ru(μ-H)}3{μ3-BO···B(C6F5)3}(μ3-H)] (5), in
which the site exchange of hydrides was retarded considerably. Complex 3 reacted with PMe3 and CO to afford [(Cp*Ru)3(μ-BO)(μ-H)3(μ3-H)(PMe3)] (6) and [{Cp*Ru(CO)}3(μ-BO)(μ-H)2] (7), respectively, which demonstrated that
the coordination mode of the BO ligand changed from a face-capping
to an edge-bridging mode at the Ru3 site.
Anions often quench fluorescence (FL). However, strong ionic hydrogen bonding between fluorescent dyes and anion molecules has the potential to control the electronic state of FL dyes, creating new functions via non-covalent interactions. Here, we propose a novel approach, utilising ionic hydrogen bonding between urea groups and anions, to control the electronic states of fluorophores and develop an aggregation-induced emission enhancement (AIEE) system. The AIEE ionic hydrogen-bonded complex (IHBC) formed between 1,8-diphenylnaphthalene (p-2urea), with aryl urea groups at the para-positions on the peri-phenyl rings, and acetate ions exhibits a remarkably high sensitivity to fluid viscosity compared with most conventional viscosity-sensitive dyes, and the FL quantum yield (QY) in ion-pair assemblies of the IHBC and tetrabutylammonium cations is more than five times higher than that of the IHBC in solution. Our versatile and simple approach for the design of AIEE dye facilitates the future development of viscosity probes and solid-state emitting materials.
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