39 research outputs found
Crystal Engineering of Vapochromic Porous Crystals Composed of Pt(II)-Diimine Luminophores for Vapor-History Sensors
A novel
PtÂ(II) diimine complex, [PtÂ(CN)<sub>2</sub>Â(H<sub>2</sub>d<i>p</i>cpbpy)] (<b>1</b>, H<sub>2</sub>d<i>p</i>cpbpy = 4,4′-diÂ(<i>p</i>-carboxyphenyl)-2,2′-bipyridine),
was synthesized, and its vapochromic behavior was investigated. The <b><u>y</u></b>ellow <b><u>a</u></b>morphous form of <b>1</b>, <b>1-Ya</b>, transformed
into the porous <b><u>o</u></b>range <b><u>c</u></b>rystalline form, <b>1-Oc</b>, upon exposure
to ethanol vapor. This behavior is similar to that of the previously
reported complex, [PtÂ(CN)<sub>2</sub>(H<sub>2</sub>dcphen)] (<b>2</b>, H<sub>2</sub>dcphen = 4,7-dicarboxy-1,10-phenanthroline).
X-ray diffraction study showed that <b>1-Oc</b> possessed similar
but larger porous channels (14.3 × 8.6 Å) compared to the <b><u>r</u></b>ed <b><u>c</u></b>rystalline form of <b>2</b>, <b>2-Rc</b> (6.4 ×
6.8 Ã…). Although the porous structure of <b>2-Rc</b> was
retained after vapor desorption, that of <b>1-Oc</b> collapsed
to form the <b><u>o</u></b>range <b><u>a</u></b>morphous solid, <b>1-Oa</b>. However, the
orange color was unchanged in this process. The initial color was
recovered by grinding <b>1-Oa</b> and <b>2-Rc</b>. These <i>vapor-writing</i> and <i>grinding-erasing</i> functions
can be applied to both in situ vapor sensing and vapor-history sensing,
i.e., sensors that can memorize the existence of previous vapors.
A notable difference was observed for humid air sensitivity; the orange
emission of <b>1-Oa</b> was largely unaffected upon exposure
to humid air, whereas the red emission of <b>2-Rc</b> was significantly
affected. The lesser sensitivity of <b>1-Oa</b> toward humidity
is important for stable vapor-history sensor applications
Vapor-Controlled Linkage Isomerization of a Vapochromic Bis(thiocyanato)platinum(II) Complex: New External Stimuli To Control Isomerization Behavior
We synthesized a novel PtÂ(II)–diimine complex
with a typical
ambidentate thiocyanato ligand, [PtÂ(<i>thiocyanato</i>)<sub>2</sub>(H<sub>2</sub>dcbpy)] (<b>1</b>; H<sub>2</sub>dcbpy
=4,4′-dicarboxy-2,2′-bipyridine), and found that the
complex <b>1</b> exhibits unique linkage isomerizations with
drastic color and luminescence changes driven by exposure to volatile
organic chemical (VOC) vapors in the solid state. Reaction between
[PtCl<sub>2</sub>(H<sub>2</sub>dcbpy)] and KSCN in aqueous solution
at 0 °C enabled successful isolation of an isomer with the S-coordinated
thiocyanato ligand, [PtÂ(<u>S</u>CN)<sub>2</sub>(H<sub>2</sub>dcbpy)] (<b>1SS·H</b><sub><b>2</b></sub><b>O</b>), as a nonluminescent orange solid. Interestingly, <b>1SS·H</b><sub><b>2</b></sub><b>O</b> was isomerized
completely to one isomer with the N-coordinated isothiocyanato ligand,
[PtÂ(<u>N</u>CS)<sub>2</sub>(H<sub>2</sub>dcbpy)] (<b>1NN·3DMF</b>) by exposure to DMF vapor, and this isomerization
was accompanied by significant color and luminescence changes from
nonluminescent orange to luminescent red. IR spectroscopy and thermogravimetric
analysis revealed that adsorption of the DMF vapor and transformation
of the hydrogen-bonded structure both played important roles in this
vapor-induced linkage isomerization. Another isomer containing both
S- and N-coordinated thiocyanato ligands, [PtÂ(<u>S</u>CN)Â(<u>N</u>CS)Â(H<sub>2</sub>dcbpy)] (<b>1SN</b>), was obtained as a nonluminescent yellow solid simply by exposure
of <b>1SS·H</b><sub><b>2</b></sub><b>O</b> to
acetone vapor at room temperature, and about 80% of <b>1SS·H</b><sub><b>2</b></sub><b>O</b> was found to be converted
to <b>1SN</b>. In the solution state, each isomer changed gradually
to an isomeric mixture, but pure <b>1SS</b> was regenerated
by UV light irradiation (λ<sub>irr.</sub> = 300 nm) of an MeOH
solution of the mixture. In the crystal structure of <b>1SN</b>, the complex molecules were hydrogen-bonded to each other through
the carboxyl groups of the H<sub>2</sub>dcbpy ligand and the N site
of the thiocyanato ligand, whereas the <b>1NN</b> molecules
in the <b>1NN·4DMF</b> crystal were hydrogen-bonded to
the solvated DMF molecules. Competition of the hydrogen-bonding ability
among the carboxyl groups of the H<sub>2</sub>dcbpy ligand, N and
S atoms of the thiocyanato ligand, and the vapor molecule was found
to be one of the most important factors controlling linkage isomerization
behavior in the solid state. This unique linkage isomerization controlled
by vapor can provide an outstanding vapochromic system as well as
a new molecular switching function driven by vapor molecules
Importance of the Molecular Orientation of an Iridium(III)-Heteroleptic Photosensitizer Immobilized on TiO<sub>2</sub> Nanoparticles
To elucidate the
effect of the molecular orientation of a photosensitizing (PS) dye
molecule on photoinduced interfacial electron transfer to a semiconductor
substrate, we have synthesized two new IrÂ(III) heteroleptic complexes
each comprising two phosphonic acid groups: [IrÂ(ppy)<sub>2</sub>(CPbpy)]<sup>+</sup> and [IrÂ(CPppy)<sub>2</sub>(bpy)]<sup>+</sup> (<b>1B</b> and <b>1P</b>, respectively; Hppy = 2-phenylpyridine, bpy
= 2,2′-bipyridine, CPbpy = 4,4′-bisÂ(methylphosphonic
acid)-2,2′-bipyridine, and CPppy = 4-(methylphosphonic acid)-2-phenylpyridine).
Both IrÂ(III) complexes exhibit similar UV–vis absorption spectra
and quasi-reversible IrÂ(IV)/IrÂ(III) redox behavior at a potential
of 1.67 V vs NHE. On the other hand, the triplet metal-to-ligand charge-transfer
(<sup>3</sup>MLCT) phosphorescence energy of <b>1B</b> was ∼0.12
eV higher than that of <b>1P</b>. This difference was attributed
to the electron-donating methyl phosphonate groups attached to the
bpy ligand that destabilize the <sup>3</sup>MLCT excited state in
which the photoexcited electron is localized in the bpy moiety. Both
IrÂ(III) PS dyes were immobilized onto the surface of the Pt-co-catalyst-loaded
TiO<sub>2</sub> nanoparticles (<b>1B@Pt-TiO</b><sub><b>2</b></sub> and <b>1P@Pt-TiO</b><sub><b>2</b></sub>). Immobilization
was comparable, suggesting that the effect of the positions of the
methyl phosphonate groups on the immobilization behavior was negligible.
On the other hand, the photocatalytic H<sub>2</sub> evolution activity
of <b>1B@Pt-TiO</b><sub><b>2</b></sub> was about 6-fold
higher than that of <b>1P@Pt-TiO</b><sub><b>2</b></sub>, indicating the importance of the methyl phosphonate anchoring group
position in regulating not only the redox potentials but also the
orientation of the molecular photosensitizer on the semiconductor
substrate
Environmentally Friendly Mechanochemical Syntheses and Conversions of Highly Luminescent Cu(I) Dinuclear Complexes
Luminescent
dinuclear CuÂ(I) complexes, [Cu<sub>2</sub>X<sub>2</sub>(dpypp)<sub>2</sub>] [<b>Cu-X</b>; X = Cl, Br, I; dpypp = 2,2′-(phenylphosphinediyl)Âdipyridine],
were successfully synthesized by a solvent-assisted mechanochemical
method. A trace amount of the assisting solvent plays a key role in
the mechanochemical synthesis; only two solvents possessing the nitrile
group, CH<sub>3</sub>CN and PhCN, were effective for promoting the
formation of dinuclear <b>Cu-X</b>. X-ray analysis revealed
that the dinuclear structure with no Cu···Cu interactions,
bridged by two dpypp ligands, was commonly formed in all <b>Cu-X</b> species. These complexes exhibited bright green emission in the
solid state at room temperature (Φ = 0.23, 0.50, and 0.74; λ<sub>em</sub> = 528, 518, and 530 nm for <b>Cu-Cl</b>, <b>Cu-Br</b>, and <b>Cu-I</b>, respectively). Emission decay measurement
and TD-DFT calculation suggested that the luminescence of <b>Cu-X</b> could be assigned to phosphorescence from the triplet metal-to-ligand
charge-transfer (<sup>3</sup>MLCT) excited state, effectively mixed
with the halide-to-ligand charge-transfer (<sup>3</sup>XLCT) excited
state, at 77 K. The source of emission changed to thermally activated
delayed fluorescence (TADF) with the same electronic transition nature
at room temperature. In addition, the CH<sub>3</sub>CN-bound analogue,
[Cu<sub>2</sub>(CH<sub>3</sub>CN)<sub>2</sub>Â(dpypp)<sub>2</sub>]Â(BF<sub>4</sub>)<sub>2</sub>, was successfully mechanochemically
converted to <b>Cu-X</b> by grinding with solid KX in the presence
of a trace amount of assisting water
Reduction in Crystal Size of Flexible Porous Coordination Polymers Built from Luminescent Ru(II)-Metalloligands
In
this study, we examined the reduction in crystal size of the
porous coordination polymers (PCPs) {Sr<sub>4</sub>(H<sub>2</sub>O)<sub>9</sub>]<b>Â[4Ru]</b><sub>2</sub>·9H<sub>2</sub>O]} (<b>Sr</b><sub><b>2</b></sub><b>[4Ru]</b>)
and [MgÂ(H<sub>2</sub>O)<sub>6</sub>]Â{[Mg<sub>2</sub>(H<sub>2</sub>O)<sub>3</sub><b>Â[4Ru]</b>·4H<sub>2</sub>O}
(<b>Mg</b><sub><b>2</b></sub><b>[4Ru]</b>) composed
of a luminescent metalloligand [RuÂ(4,4′-dcbpy)]<sup>4–</sup>Â(<b>[4Ru]</b>; 4,4′-dcbpy = 4,4′-dicarboxy-2,2′-bipyridine)
using a coordination modulation method. Scanning electron microscopy
measurements clearly show that the sizes of crystals of <b>Sr</b><sub><b>2</b></sub><b>[4Ru]</b> and <b>Mg</b><sub><b>2</b></sub><b>[4Ru]</b> were successfully reduced
to the mesoscale (about 500 nm width and 10 nm thickness for <b>Sr</b><sub><b>2</b></sub><b>[4Ru]</b> (abbreviated
as <i>m</i>-<b>Sr</b><sub><b>2</b></sub><b>[4Ru]</b>) and about 1 μm width and 30 nm thickness for <b>Mg</b><sub><b>2</b></sub><b>[4Ru]</b> (abbreviated
as <i>m</i>-<b>Mg</b><sub><b>2</b></sub><b>[4Ru]</b>)) using lauric acid as a coordination modulator. Interestingly,
the nanocrystals of <i>m</i>-<b>Sr</b><sub><b>2</b></sub><b>[4Ru]</b> formed flower-like aggregates with diameters
of 1 μm, whereas flower-like aggregates were not formed in <i>m</i>-<b>Mg</b><sub><b>2</b></sub><b>[4Ru]</b>. Water vapor adsorption isotherms of these nanocrystals suggest
that the water adsorption behavior of <i>m</i>-<b>Sr</b><sub><b>2</b></sub><b>[4Ru]</b>, which has a three-dimensional
lattice structure containing small pores, is significantly different
from that of the bulk <b>Sr</b><sub><b>2</b></sub><b>[4Ru]</b> crystal, as shown by the vapor adsorption isotherm.
In contrast, <i>m</i>-<b>Mg</b><sub><b>2</b></sub><b>[4Ru]</b>, which has a two-dimensional sheet structure,
had an adsorption isotherm very similar to that of the bulk sample.
These contrasting results suggest that the dimensionality of the coordination
framework is an important factor for the guest adsorption behavior
of nanocrystalline PCPs
Importance of the Molecular Orientation of an Iridium(III)-Heteroleptic Photosensitizer Immobilized on TiO<sub>2</sub> Nanoparticles
To elucidate the
effect of the molecular orientation of a photosensitizing (PS) dye
molecule on photoinduced interfacial electron transfer to a semiconductor
substrate, we have synthesized two new IrÂ(III) heteroleptic complexes
each comprising two phosphonic acid groups: [IrÂ(ppy)<sub>2</sub>(CPbpy)]<sup>+</sup> and [IrÂ(CPppy)<sub>2</sub>(bpy)]<sup>+</sup> (<b>1B</b> and <b>1P</b>, respectively; Hppy = 2-phenylpyridine, bpy
= 2,2′-bipyridine, CPbpy = 4,4′-bisÂ(methylphosphonic
acid)-2,2′-bipyridine, and CPppy = 4-(methylphosphonic acid)-2-phenylpyridine).
Both IrÂ(III) complexes exhibit similar UV–vis absorption spectra
and quasi-reversible IrÂ(IV)/IrÂ(III) redox behavior at a potential
of 1.67 V vs NHE. On the other hand, the triplet metal-to-ligand charge-transfer
(<sup>3</sup>MLCT) phosphorescence energy of <b>1B</b> was ∼0.12
eV higher than that of <b>1P</b>. This difference was attributed
to the electron-donating methyl phosphonate groups attached to the
bpy ligand that destabilize the <sup>3</sup>MLCT excited state in
which the photoexcited electron is localized in the bpy moiety. Both
IrÂ(III) PS dyes were immobilized onto the surface of the Pt-co-catalyst-loaded
TiO<sub>2</sub> nanoparticles (<b>1B@Pt-TiO</b><sub><b>2</b></sub> and <b>1P@Pt-TiO</b><sub><b>2</b></sub>). Immobilization
was comparable, suggesting that the effect of the positions of the
methyl phosphonate groups on the immobilization behavior was negligible.
On the other hand, the photocatalytic H<sub>2</sub> evolution activity
of <b>1B@Pt-TiO</b><sub><b>2</b></sub> was about 6-fold
higher than that of <b>1P@Pt-TiO</b><sub><b>2</b></sub>, indicating the importance of the methyl phosphonate anchoring group
position in regulating not only the redox potentials but also the
orientation of the molecular photosensitizer on the semiconductor
substrate
Vapor-Controlled Linkage Isomerization of a Vapochromic Bis(thiocyanato)platinum(II) Complex: New External Stimuli To Control Isomerization Behavior
We synthesized a novel PtÂ(II)–diimine complex
with a typical
ambidentate thiocyanato ligand, [PtÂ(<i>thiocyanato</i>)<sub>2</sub>(H<sub>2</sub>dcbpy)] (<b>1</b>; H<sub>2</sub>dcbpy
=4,4′-dicarboxy-2,2′-bipyridine), and found that the
complex <b>1</b> exhibits unique linkage isomerizations with
drastic color and luminescence changes driven by exposure to volatile
organic chemical (VOC) vapors in the solid state. Reaction between
[PtCl<sub>2</sub>(H<sub>2</sub>dcbpy)] and KSCN in aqueous solution
at 0 °C enabled successful isolation of an isomer with the S-coordinated
thiocyanato ligand, [PtÂ(<u>S</u>CN)<sub>2</sub>(H<sub>2</sub>dcbpy)] (<b>1SS·H</b><sub><b>2</b></sub><b>O</b>), as a nonluminescent orange solid. Interestingly, <b>1SS·H</b><sub><b>2</b></sub><b>O</b> was isomerized
completely to one isomer with the N-coordinated isothiocyanato ligand,
[PtÂ(<u>N</u>CS)<sub>2</sub>(H<sub>2</sub>dcbpy)] (<b>1NN·3DMF</b>) by exposure to DMF vapor, and this isomerization
was accompanied by significant color and luminescence changes from
nonluminescent orange to luminescent red. IR spectroscopy and thermogravimetric
analysis revealed that adsorption of the DMF vapor and transformation
of the hydrogen-bonded structure both played important roles in this
vapor-induced linkage isomerization. Another isomer containing both
S- and N-coordinated thiocyanato ligands, [PtÂ(<u>S</u>CN)Â(<u>N</u>CS)Â(H<sub>2</sub>dcbpy)] (<b>1SN</b>), was obtained as a nonluminescent yellow solid simply by exposure
of <b>1SS·H</b><sub><b>2</b></sub><b>O</b> to
acetone vapor at room temperature, and about 80% of <b>1SS·H</b><sub><b>2</b></sub><b>O</b> was found to be converted
to <b>1SN</b>. In the solution state, each isomer changed gradually
to an isomeric mixture, but pure <b>1SS</b> was regenerated
by UV light irradiation (λ<sub>irr.</sub> = 300 nm) of an MeOH
solution of the mixture. In the crystal structure of <b>1SN</b>, the complex molecules were hydrogen-bonded to each other through
the carboxyl groups of the H<sub>2</sub>dcbpy ligand and the N site
of the thiocyanato ligand, whereas the <b>1NN</b> molecules
in the <b>1NN·4DMF</b> crystal were hydrogen-bonded to
the solvated DMF molecules. Competition of the hydrogen-bonding ability
among the carboxyl groups of the H<sub>2</sub>dcbpy ligand, N and
S atoms of the thiocyanato ligand, and the vapor molecule was found
to be one of the most important factors controlling linkage isomerization
behavior in the solid state. This unique linkage isomerization controlled
by vapor can provide an outstanding vapochromic system as well as
a new molecular switching function driven by vapor molecules
Impact of Photosensitizing Multilayered Structure on Ruthenium(II)-Dye-Sensitized TiO<sub>2</sub>‑Nanoparticle Photocatalysts
To improve the efficiency
of photoinduced charge separation on
the surface of dye-sensitized TiO<sub>2</sub> nanoparticles, we synthesized
the RuÂ(II)-photosensitizer-immobilized, Pt-cocatalyst-loaded TiO<sub>2</sub> nanoparticles <b>RuCP</b><sup><b>2</b></sup>@Pt–TiO<sub>2</sub>, <b>RuCP</b><sup><b>2</b></sup>–Zr–<b>RuP</b><sup><b>6</b></sup>@Pt–TiO<sub>2</sub>, and <b>RuCP</b><sup><b>2</b></sup>–Zr–<b>RuP</b><sup><b>4</b></sup>–Zr–<b>RuP</b><sup><b>6</b></sup>@Pt–TiO<sub>2</sub> (<b>RuCP</b><sup><b>2</b></sup> = [RuÂ(bpy)<sub>2</sub>(mpbpy)]<sup>2–</sup>, <b>RuP</b><sup><b>4</b></sup> = [RuÂ(bpy)Â(pbpy)<sub>2</sub>]<sup>6–</sup>, <b>RuP</b><sup><b>6</b></sup> = [RuÂ(pbpy)<sub>3</sub>]<sup>10–</sup>, H<sub>4</sub>mpbpy = 2,2′-bipyridine-4,4′-bisÂ(methanephosphonic
acid), and H<sub>4</sub>pbpy = 2,2′-bipyridine-4,4′-bisÂ(phosphonic
acid)) using phosphonate linkers with bridging Zr<sup>4+</sup> ions.
X-ray fluorescence and ultraviolet–visible absorption spectra
revealed that a layered molecular structure composed of RuÂ(II) photosensitizers
and Zr<sup>4+</sup> ions (i.e., <b>RuCP</b><sup><b>2</b></sup>–Zr–<b>RuP</b><sup><b>6</b></sup> and <b>RuCP</b><sup><b>2</b></sup>–Zr–<b>RuP</b><sup><b>4</b></sup>–Zr–<b>RuP</b><sup><b>6</b></sup>) was successfully formed on the surface
of Pt–TiO<sub>2</sub> nanoparticles, which increased the surface
coverage from 0.113 nmol/cm<sup>2</sup> for singly layered <b>RuCP</b><sup><b>2</b></sup>@Pt–TiO<sub>2</sub> to 0.330 nmol/cm<sup>2</sup> for triply layered <b>RuCP</b><sup><b>2</b></sup>–Zr–<b>RuP</b><sup><b>4</b></sup>–Zr–<b>RuP</b><sup><b>6</b></sup>@Pt–TiO<sub>2</sub>. The
photocatalytic H<sub>2</sub> evolution activity of the doubly layered <b>RuCP</b><sup><b>2</b></sup>–Zr–<b>RuP</b><sup><b>6</b></sup>@Pt–TiO<sub>2</sub> was three times
higher than that of the singly layered <b>RuCP</b><sup><b>2</b></sup>@Pt–TiO<sub>2</sub>, whereas the activity of
triply layered <b>RuCP</b><sup><b>2</b></sup>–Zr–<b>RuP</b><sup><b>4</b></sup>–Zr–<b>RuP</b><sup><b>6</b></sup>@Pt–TiO<sub>2</sub> was less than
half of that for <b>RuCP</b><sup><b>2</b></sup>@Pt–TiO<sub>2</sub>. The photosensitizing efficiencies of these RuÂ(II)-photosensitizer-immobilized
nanoparticles for the O<sub>2</sub> evolution reaction catalyzed by
the CoÂ(II)-containing Prussian blue analogue [Co<sup>II</sup>(H<sub>2</sub>O)<sub>2</sub>]<sub>1.31</sub>[{Co<sup>III</sup>(CN)<sub>6</sub>}<sub>0.63</sub>{Pt<sup>II</sup>(CN)<sub>4</sub>}<sub>0.37</sub>]
decreased as the number of RuÂ(II)-photosensitizing layers increased.
Thus, crucial aspects of the energy- and electron-transfer mechanism
for the photocatalytic H<sub>2</sub> and O<sub>2</sub> evolution reactions
involve not only the RuÂ(II)-complex-TiO<sub>2</sub> interface but
also the multilayered structure of the RuÂ(II)-photosensitizers on
the Pt–TiO<sub>2</sub> surface
Effect of Water Coordination on Luminescent Properties of Pyrazine-Bridged Dinuclear Cu(I) Complexes
Two luminescent pyrazine-bridged
dinuclear CuÂ(I) complexes, namely, [{CuÂ(PPh<sub>3</sub>)<sub>2</sub>(H<sub>2</sub>O)}Â(μ-MeOpyz)Â{CuÂ(PPh<sub>3</sub>)<sub>2</sub>(CH<sub>3</sub>CN)}]Â(BF<sub>4</sub>)<sub>2</sub> and [{CuÂ(PPh<sub>3</sub>)<sub>2</sub>(H<sub>2</sub>O)}Â(μ-MeOpyz)Â{CuÂ(PPh<sub>3</sub>)<sub>2</sub>(H<sub>2</sub>O)}]Â(BF<sub>4</sub>)<sub>2</sub> (<b>H</b><sub><b>2</b></sub><b>O–Cu</b><sub><b>2</b></sub><b>–AN</b> and <b>H</b><sub><b>2</b></sub><b>O–Cu</b><sub><b>2</b></sub><b>–H</b><sub><b>2</b></sub><b>O</b>; PPh<sub>3</sub> = triphenylphosphine, MeOpyz = 2-methoxypyrazine),
were successfully synthesized and characterized by single-crystal
X-ray diffraction and luminescence measurements. X-ray analysis revealed
that the water molecules are coordinated to both CuÂ(I) ions to form
almost the same P<sub>2</sub>N<sub>1</sub>O<sub>1</sub> coordination
structure in <b>H</b><sub><b>2</b></sub><b>O–Cu</b><sub><b>2</b></sub><b>–H</b><sub><b>2</b></sub><b>O</b>, whereas one of the two Cu ions in <b>H</b><sub><b>2</b></sub><b>O–Cu</b><sub><b>2</b></sub><b>–AN</b> was coordinated by acetonitrile instead
of water to form a different P<sub>2</sub>N<sub>2</sub> coordination
environment. The asymmetric <b>H</b><sub><b>2</b></sub><b>O–Cu</b><sub><b>2</b></sub><b>–AN</b> exhibits very bright yellow-green emission with a high emission
quantum yield (λ<sub>em</sub> = 550 nm, Φ = 0.70) at room
temperature in the solid state in spite of the coordination of water
molecule, which usually tends to deactivate the emissive state through
O–H vibration. The intense emission at room temperature is
a result of thermally activated delayed fluorescence, and the remarkable
temperature dependence of emission lifetimes indicates the existence
of unique multiple emission states for the asymmetric dinuclear complex.
In contrast, the emission of <b>H</b><sub><b>2</b></sub><b>O–Cu</b><sub><b>2</b></sub><b>–H</b><sub><b>2</b></sub><b>O</b> was observed at longer wavelengths
with remarkably a lower quantum yield (λ<sub>em</sub> = 580
nm, Φ = 0.05). Time-dependent density functional theory calculations
suggested that the emission could result from the metal-to-ligand
charge-transfer transition state. However, it could be rapidly deactivated
by the structural distortion around the Cu ion with a less-bulky coordination
environment in <b>H</b><sub><b>2</b></sub><b>O–Cu</b><sub><b>2</b></sub><b>–H</b><sub><b>2</b></sub><b>O</b>
Emission Tuning of Luminescent Copper(I) Complexes by Vapor-Induced Ligand Exchange Reactions
We have synthesized
two luminescent mononuclear CuÂ(I) complexes, [CuÂ(PPh<sub>2</sub>Tol)Â(THF)Â(4Mepy)<sub>2</sub>]Â(BF<sub>4</sub>) (<b>1</b>) and [CuÂ(PPh<sub>2</sub>Tol)Â(4Mepy)<sub>3</sub>]Â(BF<sub>4</sub>) (<b>2</b>) (PPh<sub>2</sub>Tol = diphenylÂ(<i>o</i>-tolyl)Âphosphine,
4Mepy = 4-methylpyridine, THF = tetrahydrofuran), and investigated
their crystal structures, luminescence properties, and vapor-induced
ligand exchange reactions in the solid state. Both coordination complexes
are tetrahedral, but one of the three 4Mepy ligands of complex <b>2</b> is replaced by a THF solvent molecule in complex <b>1</b>. In contrast to the very weak blue emission of the THF-bound complex <b>1</b> (wavelength of emission maximum (λ<sub>em</sub>) =
457 nm, emission quantum yield (Φ<sub>em</sub>) = 0.02) in the
solid state at room temperature, a very bright blue-green emission
was observed for <b>2</b> (λ<sub>em</sub> = 484 nm, Φ<sub>em</sub> = 0.63), suggesting a contribution of the THF ligand to
nonradiative deactivation. Time-dependent density functional theory
calculations and emission lifetime measurements suggest that the room-temperature
emissions of the complexes are due to thermally activated delayed
fluorescence from the metal-to-ligand charge transfer excited state.
Interestingly, by exposing the solid sample of THF-bound <b>1</b> to 4Mepy vapor, the emission intensity drastically increased and
the emission color changed from blue to blue-green. Powder X-ray diffraction
measurements revealed that the emission change of <b>1</b> is
due to the vapor-induced ligand exchange of THF for 4Mepy, forming
the strongly emissive complex <b>2</b>. Further emission tuning
was achieved by exposing <b>1</b> to pyrimidine or pyrazine
vapors, forming green (λ<sub>em</sub> = 510 nm) or orange (λ<sub>em</sub> = 618 nm) emissive complexes, respectively. These results
suggest that the vapor-induced ligand exchange is a promising method
to control the emission color of luminescent CuÂ(I) complexes