Luminescence Tunable Europium and Samarium Complexes: Reversible On/Off Switching and White-Light Emission

DOI: 10.1021/acs.inorgchem.0c00392

Source and publish data:

Inorganic Chemistry p. 6963 - 6977 (2020)

Update date:2022-08-11

Topics:

Authors:

Chen, Jing

Xie, Ziyu

Meng, Lingyi

Hu, Ziying

Kuang, Xiaofei

Xie, Yiming

Lu, Can-Zhong

Read Full Text PDF DownLoad Join now for total 90,000,000 free articles

Article abstract of DOI:10.1021/acs.inorgchem.0c00392

Single-molecule functional materials with luminescence tunable by external stimuli are of increasing interest due to their application in sensors, display devices, biomarkers, and switches. Herein, new europium and samarium complexes with ligands having triphenylamine (TPA) groups as the redox center and 2,2′-bipyridine (bpy) as the coordinating groups and diketonate (tta) as the second ligand have been constructed. The complexes show white-light emission in selected solvents for proper mixtures of the emission from Ln³⁺ ions and the ligands. Meanwhile, they exhibit reversible luminescence switching on/off properties by controlling the external potential owing to intramolecular energy transfer from the Ln³⁺ ions to the electrochemically generated radical cation of TPA⁺. Time-dependent density functional theory (TD-DFT) calculations have been performed to study the electronic spectra. The proposed intramolecular energy transfer processes have been verified by density functional theory (DFT) studies.

Full text of DOI:10.1021/acs.inorgchem.0c00392

pubs.acs.org/IC

Article

Luminescence Tunable Europium and Samarium Complexes:

Reversible On/Oﬀ Switching and White-Light Emission

Jing Chen, Ziyu Xie, Lingyi Meng, Ziying Hu, Xiaofei Kuang, Yiming Xie, and Can-Zhong Lu*

Cite This: https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Read Online

sı

Metrics & More

Article Recommendations

Supporting Information

ACCESS

ABSTRACT: Single-molecule functional materials with lumines-

cence tunable by external stimuli are of increasing interest due to

their application in sensors, display devices, biomarkers, and

switches. Herein, new europium and samarium complexes with

ligands having triphenylamine (TPA) groups as the redox center and

2,2′-bipyridine (bpy) as the coordinating groups and diketonate (tta)

as the second ligand have been constructed. The complexes show

white-light emission in selected solvents for proper mixtures of the

emission from Ln³⁺ions and the ligands. Meanwhile, they exhibit

reversible luminescence switching on/oﬀ properties by controlling

the external potential owing to intramolecular energy transfer from

the Ln³⁺ions to the electrochemically generated radical cation of

TPA^•+. Time-dependent density functional theory (TD-DFT)

calculations have been performed to study the electronic spectra.

The proposed intramolecular energy transfer processes have been

veriﬁed by density functional theory (DFT) studies.

dyads with electroﬂuorochromic properties. So far, electro-

ﬂuorochromic molecules based on luminescent lanthanide

complexes have rarely been reported.¹⁵⁻¹⁷The Rigaut group

reported ytterbium and ruthenium d−f heterobimetallic

carbon-rich complexes, and the NIR luminescence of Yb was

controlled by the redox of the Ru moiety.¹⁵Yano and co-

workers have reported a Eu compound with a terpyridine−

triphenylamine redox ligand, showing on/oﬀ luminescence

switching properties, and they considered the energy transfer

from a diketonate moiety to a triarylamine radical cation as the

intrinsic reason for emission quenching.¹⁶All of these

lanthanide complexes are made from one redox-active moiety

and a lanthanide ﬂuorophore. It seems desirable to seek novel

lanthanide molecules with electroﬂuorochromic properties, to

study their optical properties and understand their intra-

molecular energy transfer processes and further to explore their

various applications in white-light materials, molecular

switches, ion detection, and so on.

INTRODUCTION

■

Single-molecule functional materials with luminescence tuna-

ble by external stimuli, e.g. heat,¹pH,²light,³electrons,⁴and

others,⁵have been widely studied as sensors, display devices,

biomarkers, and so on. Electroﬂuorochromic behavior was

proposed by Lehn and co-workers in 1993,⁶which means that

one material shows both electrochromic properties and

ﬂuorescence. In principle, this kind of molecule may exhibit

tunable luminescence by electronic triggering. One of the

strategies to build up this kind of molecule is choosing suitable

ﬂuorophores and redox-active electrochromic organic groups

to construct dyads, in which the intrinsic electron transfer or

energy transfer will be changed by external electronic stimuli.⁷

The typical ﬂuorophores are naphthalimide, dansyl, and

ruthenium complexes and the redox-active electrochromic

organic groups may be triphenylamine, tetrazine, quinones,

tetrathiafulvalenes, and macrocycles containing metals.

Luminescent lanthanide complexes have inspired research-

ers’ interest in recent decades due to their various photo-

luminescence properties and their optical applications such as

ampliﬁers,⁸laser materials,⁹organic light-emitting diodes

(OLEDs),¹⁰metal ion detection,¹¹cancer diagnosis,¹²

therapy,¹³and luminescent thermometers.¹⁴In addition,

luminescent lanthanide ions (e.g., Eu³⁺, Tb³⁺, Sm³⁺, Yb³⁺,

Nd³⁺, Er³⁺) in visible or/and near-infrared (NIR) regions have

long excited-state lifetimes and narrow emission bands, and

they can be promising candidates as ﬂuorophores to construct

Triphenylamine (TPA) and its derivatives are known as

electrochromic materials showing diﬀerent absorption spectra

Received: February 13, 2020

https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

pubs.acs.org/IC

Article

Scheme 1. Molecular Structures of the Ligands TPA-bpy (L₁) and TPA-xy-bpy (L₂) and Complexes 1−3

in their diﬀerent redox states. They are used in optical displays

or organic solar cells for their excellent photophysical

properties.¹⁸Recently, Lin et al. reported triphenylamine

derivatives with aggregation-induced emission (AIE) active

pendant groups having remarkable electroﬂuorochromic

behaviors.¹⁹Cai et al. studied a series of polymers with

pyrrole and triarylamine units and found that they had

excellent stability for electroﬂuorochromic properties.²⁰Mean-

while, some molecules containing organic ligands with amine

derivative moieties and lanthanide ions exhibit white-light

emission,²¹and proper mixtures of the emission from organic

ligands and lanthanide ions produce white light under some

conditions. These single-component white-light emitters have

more advantages in generating white light than the traditional

method by physical mixing of two (blue/yellow) or three (red/

blue/green) separate emitters. It is considered that they may

simplify the preparation of lighting and display devices.

Furthermore, they may avoid the drawbacks of separate

emitters such as degradation at diﬀerent rates, having diﬀerent

requirements in device production.²¹

of the organic ligands are considered to be replaced by C−F

bonds, because the C−H, O−H, and N−H bonds with high-

energy oscillators may decrease the emission intensity of Ln³⁺

ions.²⁴For example, thenoyltriﬂuoroacetone (Htta) is a good

candidate to sensitize Ln³⁺ions such as Eu³⁺, Sm³⁺, and Yb³⁺

ions.

On the basis of the consideration that we mentioned above,

the two new ligands L₁(TPA-bpy) and L₂(TPA-xy-bpy) (xy =

xylene) containing a triphenylamine (TPA) moiety as the

redox center and 2,2′-bipyridine (bpy) as the coordinating

group have been designed, synthesized, and coordinated to

Ln(tta)₃·2H₂O (Ln = Eu³⁺, Sm³⁺, Htta = 2-thenoyltriﬂuor-

oacetone)²⁵to prepare the complexes Ln(L)(tta)₃(L = L₁, Ln

= Eu (1), Sm (2); L = L₂, Ln = Eu (3)) (Scheme 1). These

new ligands and complexes have been characterized by H

NMR spectroscopy, mass spectroscopy, elemental analyses,

and infrared (IR) spectroscopy. Single crystals of the ligand L₁

and complexes 1 and 2 suitable for X-ray single-crystal

diﬀraction were obtained in dichloromethane/ethanol solution

and the structures have been determined. The UV−vis

absorption and photoluminescence properties of the ligands

and complexes have been investigated systemically in various

solvents and also in the solid state. Interestingly, white-light

emission is observed for 1−3 according to the 1931 CIE

(International Commission on Illumination) coordinate

diagram. Radiative (k_r) and nonradiative rate constants (k_nr)

have been determined from the emission lifetime τ_obsand

emission quantum yield measurements. Complexes 1 and 2

show good luminescence switching properties upon applica-

tion of an electrochemical potential. In addition, density

functional theory (DFT) calculations have been carried out to

study the photophysical properties of the ligands and

complexes, in order to further understand the energy transfer

processes.

Eu³⁺and Sm³⁺complexes have been well explored for their

emission in the visible range, though Sm³⁺also has NIR

emission. It is particularly interesting that the absorption band

of the TPA group in its one-electron-oxidized form lies in the

visible−NIR range (∼750 nm).²²Thus, with TPA groups and

Eu³⁺or Sm³⁺emitters, we anticipated molecules exhibiting

luminescence on/oﬀ switching as well as electrochromic

properties by controlling the redox states of the TPA units.

Furthermore, additional organic chromophores should be

included to sensitize Ln³⁺ions except for the redox-active

electrochromic ligand, because lanthanide ions with low

absorption coeﬃcients are diﬃcult to excite due to the

Laporte-forbidden 4f−4f transitions. β-Diketones and their

derivatives are among the most popular ligands acting as

“antennas” to harvest light and sensitize Ln³⁺ions, because of

their high thermal and chemical stability as well as their strong

ability to coordinate to Ln³⁺ions.²³To improve the

luminescence behavior of lanthanide complexes, C−H bonds

https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

pubs.acs.org/IC

Article

Figure 1. (a) X-ray crystal structure of the ligand L₁(50% probability ellipsoids, H atoms omitted for clarity). (b) Intermolecular π···π and CH···π

noncovalent interactions between the nearest neighbors of L₁. Color code: blue for N, gray for C, red for O.

and HR4000 ﬁber optic spectrometer. Luminescence decays

were measured on an LPS980 spectrometer from Edinburgh

Instruments, using an OPO laser (NT242-1K-SH/SFG-SCU-

H/2H, EKSPLA) for excitation with a pulse repetition rate of 1

kHz and excitation pulse lengths of 4−7 ns. The photo-

luminescence quantum yields were measured by a HORIBA

Jobin-Yvon FluoroMax-4 spectrometer equipped with an

integrating sphere. X-ray single-crystal diﬀraction data were

collected with a Bruker D8 Venture diﬀractometer. The initial

structure was solved by direct methods with the SHELX and

Olex2 programs and then reﬁned by full-matrix least squares

on F².²⁶All of the crystal structures have been deposited with

the Cambridge Crystallographic Database (CCDC) with ﬁle

numbers 1946992 (L₁), 1946995 (1), and 1946996 (2).

Density functional theory (DFT) was used to optimize the

geometric structures for the S₀and T₁states of the ligands. In

the framework of time-dependent density functional theory

(TD-DFT), the geometry optimization for the S₁state was

performed. The functional B3LYP combined with the basis set

6-311G* was adopted. All of the DFT and TD-DFT

calculations were carried out with the Gaussian 09 program

package.²⁷The UV−vis spectra were calculated by the TD-

DFT method with the B3LYP/6-311G* basis set.²⁸

EXPERIMENTAL

■

Materials and Instruments. All of the starting materials

(A.R. grade) and the dry solvents (THF >99.9%, DCM

>99.9%, CH₃CN >99.8%) were purchased from commercial

sources and used directly without any puriﬁcation. H NMR

spectra were measured on a Bruker Avance III instrument

operating at 400 MHz frequency. Elemental analysis of C, H,

and N was done with an Elementar Vari EL Cube instrument.

Mass spectra were recorded on a DECAX-30000 LCQ Deca

XP instrument (70 eV). The FTIR spectra were performed on

a Thermo Nicolet is50 instrument, with KBr disks in the 525−

4000 cm⁻¹region. Cyclic voltammetry was performed with

three electrodes (working electrode, Pt electrode; reference

and counter electrodes, Ag wire) on a Princeton PARSTAT

MC instrument. Dry CH₃CN with 0.1 or 0.25 M tetra-n-

butylammonium hexaﬂuorophosphate (TBAPF₆) was used as a

supporting electrolyte solution for the electrochemistry and

spectroelectrochemistry measurements. The redox potential

values were calibrated by using small amounts of ferrocene as

an internal reference. Spectroelectrochemistry was performed

with a Pt-grid electrode and two Ag wires in a thin-layer

cuvette. Optical absorption spectroscopy was done on a Cary

5000 UV−vis−NIR spectrophotometer from Agilent. Steady-

state luminescence was measured on an FLS980 apparatus

from Edinburgh Instruments or an Ocean Optics QE65PRO

https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

pubs.acs.org/IC

Article

Details of all the syntheses, characterizations, and measure-

ments of the physical properties are presented in the

Supporting Information.

RESULTS AND DISCUSSION

■

Syntheses and X-ray Crystal Structure Character-

ization. The ligands L₁and L₂were synthesized by the

Sonogashira coupling reaction²⁹of 4-ethynyl-N,N-bis(4-

methoxyphenyl)aniline and Br-bpy or I-xy-bpy (see the

Supporting Information for details). The lanthanide complexes

[Eu(tta)₃L₁] (1), [Sm(tta)₃L₁] (2), and [Eu(tta)₃L₂] (3) were

synthesized by the reaction of the corresponding [Ln(tta)₃·

2H₂O] precursors²⁵with the ligand L₁or L₂in CH₂Cl₂/

C₂H₅OH mixtures overnight. The Eu complex 3 was

synthesized to explore whether the addition of a p-xylene

spacer would aﬀect the photophysical properties. The ligands

and complexes were all characterized by H NMR, elemental

analysis, ESI-MS, and infrared (IR) spectroscopy. Single

crystals of the ligand L₁and complexes 1 and 2 suitable for

X-ray diﬀraction were obtained by diﬀusion of ethanol into the

CH₂Cl₂solutions of the corresponding compounds. Their

selected crystal data and data collection parameters are given in

Table S1 in the Supporting Information.

Figure 1 shows the structure of L₁. It crystallizes in the

monoclinic space group P2₁/c with two molecules per

asymmetric unit. In these two independent molecules, the

dihedral angles between the acetylene-bonded benzene ring

and the bipyridine plane are diﬀerent. The benzene ring

(C45−C50) is almost coplanar with the corresponding

acetylene-bonded bipyridine, twisting by 3.2°, and the

acetylene group lies in the mean plane of the bipyridine. In

the second molecule in this asymmetric unit, the benzene ring

(C13−C18) is twisted out of planarity from the bipyridine

(C1−C10) by approximately 13.3°. The dihedral angle

between the plane of C16−C19−C26 and the plane of the

bipyridine (C1−C10) is 12.5°, and it is 6.5° for the angle

between the plane of C48−C51−C58 and the plane of the

bipyridine (C33−C42). The nitrogen atoms and the

connected carbon atoms in the triphenylamine group are

coplanar; the dihedral angles between this plane and the

adjacent benzene rings are 3.8, 84.9, 89.8, 13.1, 65.8, and 59.8°,

respectively. The CC bond lengths are 1.200 and 1.197 Å,

and the C−CC angles are 174.9, 176.2, 176.5, and 178.4°

(Table S2), which indicate that the −CC− chains slightly

deviate from linearity. As shown in Figure 1b, the L₁molecules

pack together by π···π interactions between adjacent

bipyridine−CC−C₆H₄moieties and CH···π weak inter-

actions to form a 3D network.

The single-crystal X-ray diﬀraction studies revealed that

complexes 1 and 2 are isostructural. They both crystallize in

the monoclinic space group P2₁/c, and their selected bond

lengths and angles are given in Table S2. Here, complex 1 is

taken as an example to describe their structures in detail. The

asymmetric unit of 1 contains one ligand L₁, one Eu³⁺ion, and

three tta ligands. As depicted in Figure 2a, the Eu³⁺ion is 8-

fold coordinated by two N atoms from the bipyridine moieties

in L₁and six O atoms from three bidentate β-diketonate tta

ligands with Eu−N bond lengths of 2.598 and 2.627 Å, as well

as Eu−O bond lengths of 2.350−2.396 Å. The coordination

number of 8 is common for Eu³⁺complexes; the average Eu−

O distance is 2.21 Å and that is 2.59 Å for average Eu−N

distance.³⁰Obviously, the Eu−O and Eu−N bond lengths of

complex 1 are close to these average values. The coordination

Figure 2. (a) ORTEP drawing of Eu(tta)₃L₁(1). Hydrogen atoms are

omitted for clarity, and thermal ellipsoids are shown at 50%

probability. (b) Coordination polyhedron of the central Eu³⁺(1)

ion. Color code: blue for N, gray for C, red for O, purple-red for Eu.

polyhedron of the Eu³⁺center is illustrated in Figure 2b; the

Eu atom ﬁnds itself in a distorted-trigonal-dodecahedral

coordination geometry. The distance from Eu to the N atom

in the triphenylamine group is about 11.624 Å. The C−CC

angles are 176.0 and 174.7°, deviating from linearity more

strongly than in the free ligand L₁, and the CC bond length

is 1.198 Å. The plane of the benzene ring (C13−C18) deviates

from the bipyridine plane by about 12.3°. In the triphenyl-

amine moiety, the dihedral angles between the CC bond

connected phenyl plane and the methoxyl group connected

phenyl planes are 49.0 and 84.2°, and these benzene planes

deviate from the C16−C19−C26 plane by about 26.4, 71.2,

and 28.3°, respectively. The structure of complex 2 is shown in

Figure S1. It has longer Ln−N and Ln−O distances and

smaller N−Ln−N and O−Ln−O angles in comparison with

complex 1, because Sm³⁺has a larger ionic radius of 1.079 Å in

comparison with that of 1.066 Å for Eu³⁺(Table S2).³¹

Optical Absorption and Emission Spectroscopy of

the Ligands L₁and L₂. The absorption and emission spectra

of the free ligands L₁and L₂were measured in diﬀerent

solvents to study the solvatochromism phenomena. The

absorption and emission spectra, absorption and emission

λ_maxvalues, molar absorption coeﬃcients, and corresponding

Stokes shift of L₁are shown in Figures 3a and 4 and Table S3.

In diﬀerent solvents, the two maximum absorption peaks of L₁

are localized at ∼290 and ∼380 nm with a subtle solvent eﬀect

(Table S3). It has the largest and smallest molar absorption

coeﬃcients in CH₂Cl₂(9.16 × 10⁴M⁻¹cm⁻¹) and ethanol

(0.78 × 10⁴M⁻¹cm⁻¹) for the ∼380 nm absorption band,

respectively. The ﬁrst band at ∼290 nm is assigned to the bpy-

localized π → π* transition,³²and the second band at ∼380

nm is an intramolecular charge transfer band. DFT calculations

https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

pubs.acs.org/IC

Article

Figure 5. Frontier orbitals with their charge density representations of

L₁and L₂as calculated by DFT (B3LYP/6-311G*).

charge transfer band from the HOMO to the LUMO moves to

∼360 nm (Figure 3b and Table S4) in comparison to L₁, with

the largest and smallest molar absorption coeﬃcients in THF

(4.22 × 10⁴M⁻¹cm⁻¹) and ethanol (1.32 × 10⁴M⁻¹cm⁻¹).

Presumably, the torsion angle between the p-xylene and

bipyridine moieties changes the full π-conjugation of the

molecule, increasing the energy of the intramolecular charge

transfer transition. Furthermore, the larger HOMO−LUMO

energy gap for L₂in comparison with L₁is veriﬁed by the DFT

calculations (Table S5).

Figure 3. Absorption spectra of L₁(a) and L₂(b) in diﬀerent

solvents.

The emission spectra of the ligands are strongly dependent

on the selected solvents (Figure 4 and Figure S3 and Tables S3

and S4). A signiﬁcant red shift in the emission of L₁was

observed, with the luminescence band maximum changing

from 473 nm in toluene to 547 nm in chloroform and 585 nm

in ethanol (Figure 4). Very weak emission bands at ∼440 and

∼600−650 nm were found in methanol, acetone, dimethyl

sulfoxide (DMSO), N,N-dimethylformamide (DMF), and

acetonitrile (Figure S3). The emission of L₂also shows a

pronounced red shift from 445 nm in toluene to 544 nm in

dichloromethane and to 620 nm in acetonitrile (Figure S3).

From Tables S3 and S4 we can see that, in the same solvent,

the emission bands of L₂are blue-shifted in comparison to the

corresponding emission bands of L₁. We tentatively attribute

this to the xylene group, which increases the excited energy

level of L₂.

Optical Absorption Spectroscopy of Complexes 1−3.

The electronic spectra of complexes 1−3 were recorded in

diﬀerent solvents with a concentration of 2 × 10⁻⁵M at room

temperature (Figure 6 and Figure S4). The absorption

maximum values and corresponding molar absorption

coeﬃcients are collected in Table S6. In most solvents,

complex 1 shows two intense absorption bands at ∼290 and

∼340 nm, which are assigned to the π → π* transitions of the

bpy and tta moieties.³³Furthermore, in most solvents there is a

shoulder near 390 nm, whereas in dichloromethane and

toluene that shoulder becomes observable as a separate band

Figure 4. Emission spectra of L₁in diﬀerent solvents at room

temperature (λ_ex≈ 380 nm).

with the Gaussian 09 program (Figure 5) demonstrate that this

intramolecular charge transfer (CT) transition is from the

HOMO mainly localized on the TPA group to the LUMO

mainly localized on the bpy group. Both the HOMO and the

LUMO have signiﬁcant contributions to the CC alkynyl

linker, indicating that there is strong electronic coupling

between the TPA and the bipyridine ligand. This will be

important for the energy transfer studies reported below. TD-

DFT calculations for the single-crystal structure of L₁without

optimization was carried out by the G09 program, using the

B3LYP function with the basis set 6-311G*, which was able to

compute absorption spectra that were similar to the spectra

with two experimentally observed absorption bands centered at

282 and 378 nm (Figure S2). For ligand L₂, the intramolecular

https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

pubs.acs.org/IC

Article

angle between the bpy group and the ethynyl-connected

benzene group of TPA in complex 3 (the Cartesian

coordinates of all the optimized geometries are shown at the

end of the Supporting Information). Consequently, the

intramolecular charge transfer of complex 3 is weakened.

DFT calculations for the absorption spectra of complexes 1

and 3 with their optimized structures also conﬁrm that 1 has

one pronounced intramolecular charge transfer band, but for 3,

this band is not observable (Figure S5).

Solid-State and Solution PL Properties of Complexes

1−3. The steady-state room temperature photoluminescence

(PL) of complexes 1−3 was measured in diﬀerent solvents and

in the solid state by exciting them at ∼340 nm according to

their absorption maximum values, respectively, and their

spectra are shown in Figure 7 and Figure S6. The observed

spectral data, lifetimes, and quantum yields of the complexes

are collected in Table 1 and in Tables S6 and S7.The emission

spectra of the Eu complexes 1 and 3 in the solid state (Figure

S6) exhibit typical 4f−4f transitions of ⁵D₀→ ⁷F_J(J = 0−4) at

580, 591, 612, 652, and 702 nm. The addition of the p-xylene

group also increases the asymmetric ligand ﬁelds around Eu

ions in complex 3, resulting in the emission intensity of ⁵D₀→

⁷F₀and D₀→ F₂transitions changing in comparison with

complex 1, especially for the ⁵D₀⁷F₂hypersensitive

→

transition (Figure S6). The emission of Sm complex 2 in the

solid state yields relatively broad bands, observed at about 562,

597, 644, and 705 nm, which are assigned to the G_5/2→ H_J

(J = 5/2, 7/2, 9/2, 11/2) transitions, and very tiny signals at

875 (⁴G_5/2

→ →

⁶F_1/2) and 945 (⁴G_5/2⁶F_5/2) nm were

detected belonging to the NIR emission of Sm³⁺(Figure S6).

The time-resolved emission decay measurements reveal

biexponential decays with lifetimes of 0.7 and 2.9 μs for 1,

1.2 and 7.0 μs for 2, and 39.4 and 220 μs for 3, respectively.

There are two hypotheses in the literature to explain this

biexponential decay: (i) a back transfer from the metal to the

triplet state of the organic ligand and (ii) the radiative decay of

two diﬀerent excited species.^34aFujiwara et al. observed a

biexponential decay of two Eu complexes with 4,4,4-triﬂuoro-

1-(2-thienyl)-1,3-butanedione and 4,7-diphenyl-1,10-phenan-

throline disulfonate ligands at the toluene−water interface,^34b

and one is Eu(tta)₂bps⁻(long lifetime) and another is

Eu₂(tta)₂(bps)₂(short lifetime). That seems not possible in

our case because the lifetimes of our complexes were obtained

in the solid state. Therefore, the possible reason for these

biexponential decays is the back transfer from the metal to the

triplet state of the organic ligand. Complexes 1 and 3

luminesce with quantum yields of 0.3% for 1 and 8.7% for 3

in the solid state at room temperature following excitation at

340 nm. The underlying reason for the lower quantum yield of

1 is probably that ligand L₁has lower energy levels, in favor of

energy transfer from Eu³⁺ions to the ligands.

In solution, the steady-state emission spectra of the three

complexes exhibit strong solvent eﬀects; their absorption and

emission data are summarized in Table S6. Complexes 1 and 3

show the typical emission of Eu³⁺ions, with emission bands at

around 580, 591, 612, 652, and 702 nm, which are assigned to

⁵D₀→ ⁷F_J(J = 0−4) transitions of Eu³⁺in more polar solvents

such as DMSO, DMF, acetone, C₂H₅OH, CH₃OH, and

CH₃CN. However, additional emission bands attributable to

the free ligands L₁and L₂are present in less polar solvents, e.g.,

CH₂Cl₂, CH₃Cl, THF, toluene, and ethyl acetate (EAC)

(Figure 7). Complex 1 shows the emission of the ligand L₁at

about 470 nm (toluene), ∼535 nm (CHCl₃, EAC, and THF),

Figure 6. Absorption spectra of complexes 1 and 3 in diﬀerent

solvents.

with a peak at ∼410 nm. We speculate that the shoulder at

∼390 nm and the absorption band at ∼410 nm are due to

intramolecular charge transfer absorption, similar to what was

observed above for the free ligands. In toluene and

dichloromethane, the absorption band belonging to the π →

π* transition of the tta group are slightly blue shifted to ∼330

nm, and this increases the spectral separation of π → π* and

charge transfer absorption bands in these two particular

solvents. The Sm complex 2 has similar absorption spectra in

diﬀerent solvents with absorption maxima at ∼340 nm and also

an absorption band at around 410 nm in both dichloro-

methane and toluene. The Eu complex 3 only shows two

obvious absorption maxima at ∼290 and ∼340 nm in diﬀerent

solvents with a very small shift. No obvious absorption band

around ∼410 nm or tiny shoulder around 390 nm is found in

the spectra, likely due to the xylene group introduced into the

ligand, which changes its conjugation. Although we did not

obtain the single-crystal structure of complex 3, we may try to

study the diﬀerence in the structures of 1 and 3 by the DFT

calculation results. In the optimized geometries of complexes 1

and 3, the dihedral angle between the bpy plane and the

ethynyl connected benzene unit is only 7.56° for complex 1

but 49.58° for the complex 3. The dihedral angle between the

p-xylene unit and the bpy plane is about 45.56°, and the p-

xylene and the ethynyl-connected benzene are almost coplanar

with a dihedral angle of 3.98° in complex 3. From these data

we may see that the addition of p-xylene unit changes the

conjugation of the ligands, and there is a nearly 50° torsion

https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

pubs.acs.org/IC

Article

Figure 7. Emission spectra of complexes 1 (a), 2 (c), and 3 (e) in diﬀerent solvents (2 × 10⁻⁵M) with ∼340 nm excitation and the white-light

emission CIE color gamuts of complexes 1 (b) cross 1 (EAC, λ_ex= 343 nm) and cross 2 (THF, λ_ex= 348 nm), 2 (d) cross 1 (DCM, λ_ex= 334 nm),

cross 2 (DCM, λ_ex= 426 nm), and cross 3 (toluene, λ_ex= 355 nm), and 3 (f) cross 1 (CHCl₃, λ_ex= 343), cross 2 (EAC, λ_ex= 344 nm), and cross 3

(THF, λ_ex= 348 nm).

and 554 nm (DCM). For complex 3, the emission bands

belonging to the ligand L₂are blue-shifted by about 25−45 nm

in comparison with complex 1, because the introduction of the

p-xylene spacer in the ligand L₂increases the energy levels of

the excited states of the ligand, which is also veriﬁed by DFT

calculations (Table S5), as noted above.

Table 1. Photophysical Properties of Complexes 1−3 in

CH₃CN Solution at Room Temperature

complex

(%)

2.6

τ_obs(μs)

k_r(s⁻¹

)

k_nr(10³s⁻¹

)

646

104

646

40.2

1.51

1.8

27.9

1.52

The Sm complex may in principle show emission not only in

the visible but also in the NIR region. Indeed, weak emission at

883 and 950 nm is observed on excitation of complex 2 at 340

nm in CH₃CN (Figure S7), due to the ⁴G_5/2→ ⁶F_1/2and ⁴G_5/2

Emission quantum yields of the complexes following excitation at

340 nm in CH₃CN. Excited-state lifetimes of the complexes

following excitation at 340 nm in CH₃CN k_r= Φ/τ_obs

. k_nr= 1/

τ_obs− k_r.³⁵

→

⁶F_5/2transitions of Sm³⁺. Here, we will focus on the

emission in the visible region of complex 2. Clearly, complex 2

https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

pubs.acs.org/IC

Article

exhibits diﬀerent photoluminescence properties in comparison

with complexes 1 and 3. In more polar solvents such as

acetonitrile and acetone, the emission of Sm³⁺ions exhibits

peaks at about 560, 598, 645, and 705 nm in the visible region,

complex 2 is excited at 334 and 426 nm in DCM or at 355 nm

in toluene, it may generate white-light emission with CIE

coordinates of (0.34, 0.30) (cross 1 in Figure 7d), (0.34, 0.33)

(cross 2 in Figure 7d), and (0.33, 0.35) (cross 3 in Figure 7d),

respectively. The Eu complex 3 generates white-light emission

when it is excited at 343 nm in CHCl₃(0.31, 0.31) (cross 1 in

Figure 7f), at 344 nm in EAC (0.33, 0.31) (cross 2 in Figure

7f), and at 348 nm in THF (0.33, 0.32) (cross 3 in Figure 7f).

It is obvious from Figure 7a,c,e that the corresponding

complexes in the respective solvents exhibit emission both

from the ligands and from the Ln³⁺ions, and the proper

mixtures of emissions from Ln³⁺ions and the ligands produce

the white light.

which are assigned to the 4f−4f transitions G_5/2→ H_5/2

⁴G_5/2

→ , → →

⁶H_7/2⁴G_5/2⁶H_9/2, and G_5/2⁶H_11/2

respectively. However, unlike complexes 1 and 3, in methanol,

ethanol, DMF, and DMSO, complex 2 shows not only the

intense emission of Sm³⁺ions but also a weak emission of the

L₁ligand at about 430 nm. In less polar solvents such as

dichloromethane, chloroform, THF, and ethyl acetate (EAC),

it exhibits strong and broad emission of the ligands and weak

emission of Sm³⁺ions. In toluene, 2 only shows a strong

emission band from the ligand, which is diﬀerent from the case

for the Eu complexes. These diﬀerent solvent-dependent

luminescent behaviors of complexes 1 and 3 on the one hand

and complex 2 on the other hand are due to the diﬀerent

excited energy levels of Eu³⁺(⁵D₀) and Sm³⁺(⁴G_5/2).

Electrochemistry and UV/Vis/NIR Spectroelectro-

chemistry Studies. The electrochemical properties of the

lanthanide complexes 1−3 were explored by cyclic voltamme-

try (CV) in acetonitrile solution with (n-C₄H₉)₄NPF₆as the

electrolyte (0.1 mol dm⁻³). Cyclic voltammograms are shown

in Figure S10 in the Supporting Information. Complexes 1−3

display one reversible one-electron oxidation with half-wave

potentials of 0.36, 0.38, and 0.30 V (vs. Fc⁺/Fc), respectively.

These oxidation waves are attributed to the TPA^•+/TPA redox

couples in the ligands L₁and L₂, whose radical cations are

stable on the voltammetric time scale due to the high degree of

chemical reversibility. The Eu complexes 1 and 3 show

irreversible reductions of the metal center at about −2.15 and

−2.20 V, respectively. The Sm complex 2 does not show any

redox signal for the metal center. Actually, it has been reported

in the literature that the E_pcvalue of Eu^3+/2+is −1.78 V (vs

Fc⁺/Fc) for the complex [Eu(BPPA)₂]OTf and −1.77 V (vs

Fc⁺/Fc) for [Eu(BPA)₂]OTf, and the value is even more

negative and not observable for the complex [Eu(MPA)₂K]

The time-resolved emission of complexes 1−3 was studied

by monitoring the samples at 612 nm (⁵D₀→ F₂) for the Eu

complexes and at 645 nm (⁴G_5/2→ ⁶H_9/2) for the Sm complex

in diﬀerent solvents (Figure S8). In all investigated solvents,

single-exponential decays with lifetime on the microsecond

time scale were obtained (Table S7). Complex 1 has the

largest τ_obsvalue of 712 μs in DMSO and the smallest τ_obs

value of 232 μs in MeOH. Complexes 2 and 3 have their

largest τ_obsvalues in CH₃CN of 104 μs for 2 and 646 μs for 3,

and the smallest τ_obsvalues of 16 μs for 2 and 279 μs for 3

occur in MeOH. In CH₃CN solution, all of these complexes

exhibit pure emission of Ln³⁺(and no ligand emission);

therefore, we take their quantum yields and the lifetime values

obtained in CH₃CN to determine the radiative (k_r) and

nonradiative (k_nr) excited-state decay rate constants of these

complexes, and all of the selected data are summarized in

Table 1.

under the same conditions.³⁷Normally, the E_1/2(Sm^3+/2+

)

value should be more negative than E_1/2(Eu^3+/2+) as reported

in the literatures.^37,38That is the reason that complex 2 does

not present any redox event. Such negative reduction potential

for these complexes make the photoinduced electron transfer

from the TPA group to the excited Ln³⁺ions impossible

according to the Rehm−Weller equation.³⁹

The luminescence quantum yields for the Eu complexes 1

and 3 are 2.6% and 1.8%, and the corresponding k_rvalues for 1

and 3 are 40.2 and 27.9 s⁻¹in CH₃CN solution, respectively.

From Table 1, we can see that complex 1 shows close k_rand k_nr

values in comparison with complex 3 in CH₃CN. The emission

of Sm complex 2 is too weak to allow evaluation of its quantum

yield both in the solid state and in CH₃CN solution.

Triphenylamine derivatives have good electrochromic

properties; normally their UV−vis absorption spectra change

upon oxidation.²²To investigate the absorption spectra

variation with applied electrochemical potential, the accessible

redox states of complex 1 were produced in a thin-layer cuvette

with an Ag wire as the reference electrode, a Pt rod as the

counter electrode, and a Pt net as the working electrode. A

deaerated CH₃CN solution with 0.25 mol dm⁻³(n-

C₄H₉)₄NPF₆as the supporting electrolyte was used. At an

applied potential of 1.2 V vs Ag⁺/Ag, the spectroelectrochem-

istry was studied. Figure 8 shows the spectral changes of

complex 1. Upon oxidation, the absorption band at about 340

nm decreases, and a new absorption band at 760 nm appears,

which is assigned to the absorption of the radical cation

TPA^•+. This is also conﬁrmed by measuring the absorption

spectra of the oxidized 1^•+generated by addition of 1 equiv of

ceric ammonium nitrate (CAN) oxidant (Figure S11).

Luminescence Control and Tuning by Applying an

Electrochemical Potential. To explore luminescence switch-

ing upon application of an external potential for complexes 1

and 2, their emission spectra were measured as a function of

electrochemical potential. Using the same experimental setup

as in the UV/vis/NIR spectroelectrochemistry study, the

emission spectra were detected in a thin-layer cuvette.

White-Light Emission. Single-component white-light

emitters have attracted increasing attention, as they will in

principle simplify the preparation of optical display devices by

avoiding the mixing of two (blue/yellow) or three (red/blue/

green) separate components. According to the 1931 CIE

(International Commission on Illumination) coordinate

diagram, standard white light should have the CIE coordinates

(0.33, 0.33). Recently, some lanthanide complexes were

reported as white-light emitters.³⁶The white-light emission

of complex 2 in EAC solution under a 365 nm UV lamp

excitation (Figure S9) inspired us to study the application

potential of complexes 1−3 as white-light-emitting materials.

The room-temperature emission spectra of complexes 1−3

in diﬀerent solvents and the corresponding chromaticity

diagrams in selected solvents are shown in Figure 7, which

reveals that the CIE coordinates of these complexes

(summarized in Tables S8 − S10) may indeed be located

favorably in the white-light region. The CIE coordinates of

complex 1 are (0.31, 0.33) (cross 1 in Figure 7b) in ethyl

acetate (EAC) on excitation at 343 nm and (0.31, 0.31) (cross

2 in Figure 7b) in THF on excitation at 348 nm. When

https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

pubs.acs.org/IC

Article

Ag⁺/Ag) was applied in the solution inside the cuvettes, the

emission signals were strongly quenched (the red curves in

Figure 9a,b), and when the potential was changed to −0.3 V

(vs Ag⁺/Ag), the emission was almost completely recovered

(the blue curves in Figure 9a,b). To test the reversibility of

luminescence switching of complexes 1 and 2, six cycles of 1 →

1^•+→ 1 and 2 → 2^•+→ 2 emission measurements were

performed in our setup, and the luminescence switching

spectra were detected. The emission intensities at 612 nm for 1

and 645 nm for 2 were considered to make graphs of the on/

oﬀ switching experiments (Figure 9c−f). After six cycles, the

emission intensity decreased to 86% of the initial intensity for

1 and 82% for 2. From their emission spectra of the last

recovery, no additional emission signals were detected and the

emission intensity decrease perhaps came from small amounts

of oxygen involved in the solution during the measurements.

The underlying reason for the luminescence switching is

Figure 8. UV/vis/NIR spectroelectrochemistry in CH₃CN/(n-

C₄H₉)₄NPF₆: oxidation of 1 to 1^•+at a potential of 1.2 V vs Ag⁺/

Ag. The asterisk marks an instrumental artifact caused by a lamp

changeover in our spectrometer.

•+

energy transfer from the Eu³⁺or Sm³⁺ions to the L₁radical

cation, which will be discussed in the following section.

Inﬂuence of the Chemical Oxidant CAN on Lumines-

cence. In principle, chemical oxidants should also be able to

oxide the complexes and produce the TPA^•+radical cations

with the positive charge localized,^22,32which may then induce

Complexes 1 and 2 show pure emission of Eu³⁺and Sm³⁺ions

in CH₃CN in their neutral forms (see the black curves in

Figure 9a,b), but no ligand emission. When 1.2 V potential (vs

Figure 9. Luminescence switching study of complexes 1 and 2 by investigation of the emission signal at 612 nm of 1 (a, c, e) and at 645 nm of 2 (b,

d, f) in deaerated acetonitrile with 0.25 M (n-C₄H₉)₄NPF₆by alternating the applied electrochemical potential between 1.2 V and −0.3 V (vs Ag⁺/

Ag).

https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

pubs.acs.org/IC

Article

Figure 10. Emission spectra and luminescence decay curves for complexes 1 (a, b), 2 (c, d) and 3 (e, f) with and without 1 equiv CAN in CH₃CN

solution (λ_ex= 340 nm, λ_em= 612 nm for 1 and 3, λ_em= 645 nm for 2).

the intramolecular energy transfer from Eu³⁺or Sm³⁺ions to

−1

k_ET= τ

⁻¹− τ_ref

complex

(1)

TPA^•+, resulting in luminescence quenching similar to that

observed above. To explore this aspect, 1 equiv of ceric

ammonium nitrate (CAN) was used to oxidize complexes 1−3

in acetonitrile. Upon excitation of the complexes at 340 nm,

their corresponding steady-state emission spectra and time-

resolved photoluminescence decay with and without CAN

were studied. Figure 10 shows that the 612 nm emissions of Eu

complexes 1 and 3 are almost completely quenched, but for the

Sm complex 2, the emission at 645 nm is only partially

quenched.

Intramolecular Energy Transfer in the Neutral and

Oxidized Forms of Complexes 1 and 2. The above

observations strongly point to intramolecular energy transfer,

and it is desirable to understand these energy transfer

processes between the ligands and the Ln³⁺ions in greater

detail. According to the energy transfer mechanism in

lanthanide complexes proposed by Crosby et al.,⁴¹the energy

level match between the Ln³⁺ions (⁵D₀for Eu³⁺in 1, ⁴G_5/2for

Sm³⁺in 2) and the triplet states of the free ligands (tta and L₁)

strongly aﬀects the luminescence properties of the lanthanide

complexes. There are two ligands, L₁and tta, in complexes 1

and 2. To clarify the intramolecular energy transfer processes

in our complexes, the relevant singlet and triplet energy levels

of L₁and tta ligands should be identiﬁed. As reported in the

literature,⁴²the tta ligand has an excited singlet energy of 3.12

eV (25164 cm⁻¹) and its triplet energy is 2.35 eV (18954

cm⁻¹). The UV−vis absorption edge of L₁in CH₃CN at room

temperature is estimated as its singlet energy level. The lower

wavelength emission peaks of the phosphorescence spectra of

the gadolinium complex at 77 K is used to calculate the triplet

energy level of L₁, because the lowest excited energy level of

Gd³⁺ions (⁶P_7/2) is very high (3.99 eV, 32150 cm⁻¹),⁴³and

therefore energy transfer cannot interfere. The absorption edge

of L₁(Figure 3a) is 460 nm, corresponding to 21739 cm⁻¹

(2.70 eV). The lower wavelength emission peak of the GdL₁

complex at 77 K is 506 nm (2.45 eV, 19762 cm⁻¹) (Figure

We also compared the time-resolved luminescence decays of

complexes 1−3 in their neutral and oxidized forms in CH₃CN

solution. Three identical single-exponential decays were

observed, and the lifetimes of the excited states were

determined as 646 μs (1 and 3) and 104 μs (2) (Table 1).

When they were oxidized by 1 equiv of CAN, the excited-state

lifetimes of the one-electron-oxidized forms were 102 (1^•+), 66

(2^•+) and 117 (3^•+) μs, respectively. We take Eu(tta)₃bpy and

Sm(tta)₃bpy as the reference complexes, whose excited-state

lifetimes are 630 and 85 μs (Figure S12). The energy transfer

rate constants k_ETfor Ln(III)* → TPA^•+(the positive charge

localized on the TPA moiety of ligands) in complexes 1^•+, 2^•+

and 3^•+can be calculated as 8.2 × 10³, 3 × 10³and 6.9 × 10³

s⁻¹according to eq 1,⁴⁰where τ_complexis the excited-state

lifetime of complexes 1^•+, 2^•+, and 3^•+and τ_refis the lifetime of

the excited state of reference complex Eu(tta)₃bpy or

Sm(tta)₃bpy.

https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

pubs.acs.org/IC

Article

S13). The energy levels of the relevant excited states for the

ligands L₁and tta are summarized in Table 2.

Table 2. Relevant Excited-State Energies of L₁, L₁^•+, tta,

Eu³⁺, and Sm³⁺

entry

singlet energy level (eV/cm⁻¹

)

triplet energy level (eV/cm⁻¹

)

tta

L₁

3.12/25164

2.70/21739

1.65/13333

2.35/18954

2.45/19762

•+

L₁

<1.65/<13333

Eu³⁺

2.02/17500 (⁵D₀−⁷F₂)

Sm³⁺

1.91/17900(⁴G_5/2−⁶H_9/2

)

In this case, it is the lowest excited energy level of L₁^•+, not the

triplet energy level. Energy estimate taken from the most intense

emission line of Ln³⁺.

As a rule of thumb, the energy diﬀerence between the triplet

excited state of ligands and the emitting energy level of Ln³⁺

should be between 2500 and 4000 cm⁻¹for eﬃcient energy

transfer.^44,45The emissive D₀excited state of Eu³⁺is at an

energy of 17500 cm⁻¹.⁴⁶The energy level diﬀerence between

T₁of L₁and D₀of Eu³⁺is only 2262 cm⁻¹, which suggests

that the energy transfer of T₁→ D₀is not very eﬃcient,

resulting in the possibility of backward energy transfer from the

metal to the ligand. Moreover, the energy level diﬀerence

between the singlet and triplet excited states of L₁is only 1977

cm⁻¹, signiﬁcantly less than 5000 cm⁻¹, which may in principle

lead to the back intersystem crossing from the T₁to S₁excited

state of L₁. The intersystem crossing of S₁→ T₁can be very

Figure 11. Intersystem crossing (ISC) and energy transfer (ET)

processes in 1 (a) and 1^•+(b).

eﬀective only when the energy gap ππ*−³ππ* is greater than

5000 cm⁻¹according to Reinhoudt’s empirical rule.⁴⁷An

energy level diagram and possible energy transfer processes are

summarized in Figure 11. Diﬀerent plausible reaction

sequences are as follows. (i) The tta ligands absorb excitation

light, and intersystem crossing from the S₁to T₁excited state

ΔE(¹ππ*−³ππ*) value of L₁is 1152 cm⁻¹, and the energy

diﬀerences between T₁of L₁and the emitting level of Ln³⁺are

74 (⁵D₀of Eu³⁺) and −326 (⁴G_5/2of Sm³⁺) cm⁻¹. Such small

values do not favor energy transfer from L₁to Ln³⁺, and

backward energy transfer can lead to the emission of L₁, which

is in agreement with the experimental results. However,

considering the possible dissociation of ligands from the

complexes in some solvents, the ligand-centered emission

perhaps comes from the dissociated ligands. The dissociation

of ligands from the complexes may change the ligand ﬁelds

around Ln³⁺, which will lead to diﬀerent excited species with

diﬀerent lifetimes. The single-exponential decays of the

complexes in diﬀerent solvents (Table S7 in the Supporting

Information) indicate that the dissociation of ligands from the

complexes is not enough to change the ligand ﬁelds of Ln³⁺,

and it can be ignored due to the tiny amount. Therefore, we

will not discuss the possibility that the dissociation of ligands

from the complexes results in the ligand-centered emission

here in detail.

of tta occurs. Subsequently, energy transfer to the D₀excited

state of Eu³⁺to sensitize the characteristic red emission of Eu³⁺

occurs. (ii) The L₁ligand harvests energy and intersystem

conversion from its S₁to its T₁level takes place; however, the

reverse intersystem crossing may occur due to the small energy

gap ππ*−³ππ* (1977 cm⁻¹), leading to the ligand-centered

ﬂuorescence from S₁, as well as some energy transfer from T₁

of L₁to D₀of Eu³⁺.

The energy levels of L₁are of key importance for the

intramolecular energy transfer in complexes 1 and 2. On the

basis of the emission spectra (Figure 4 and Figure S3), it is

clear that the energies of the relevant excited states of the

ligands vary in diﬀerent solvents according to the emission

spectra. When the ΔE(¹ππ*−³ππ*) value of the ligand is high

enough to prevent the reverse intersystem crossing, complex 1

exhibits pure red emission of Eu³⁺. Otherwise, the emission

spectra exhibit mixed ligand-centered emission and Eu³⁺ion

emission, leading to spectacular white-light luminescence. For

As we know, TPA^•+may be oxidized to a TPA radical

dication, and one may suppose that the photoinduced electron

transfer can happen in the oxidized complexes. TPA^•+is

reported to be oxidized to its radical dication at 0.8 V vs Fc⁺/

Fc.⁴⁸On the basis of the reduction potential of Ln^3+/2+and the

excited energy of Ln³⁺, the ΔG° value for the photoinduced

electron transfer in the oxidized complexes will be more than

0.63 eV for complex 1 and even more postitive for complex 2

according to the Rehm−Weller equation. It is obviously

thermodynamically impossible for photoinduced electron

transfer from TPA^•+to the excited Ln³⁺to occur. When

complex 1 or 2 was oxidized, a new band at 760 nm (1.65 eV,

Sm complex 2, the G_5/2energy level of Sm³⁺is located at

17900 cm⁻¹,⁴⁷400 cm⁻¹higher than the ⁵D₀state of Eu³⁺, and

the energy diﬀerence between T₁of L₁and G_5/2of Sm³⁺is

only 1862 cm⁻¹, leading to more eﬃcient backward energy

transfer from G_5/2of Sm³⁺to the T₁state of L₁and further

intersystem crossing to the S₁state of L₁, which results in more

S₁emission from L₁in some less polar solvents (Figure 7 and

Figure S14). Furthermore, according to our DFT calculations,

the S₁and T₁energies of L₁are 2.32 eV (18726 cm⁻¹) and

2.18 eV (17574 cm⁻¹), respectively. Thus, the

https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

pubs.acs.org/IC

Article

13333 cm⁻¹) belonging to the absorption of the nonemissive

contacting The Cambridge Crystallographic Data Centre, 12

Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

TPA^•+appeared, and the corresponding excited energy levels

•+

of L₁should be below 1.65 eV. The energy diﬀerence

between the Ln³⁺and excited energy level of L₁is therefore

•+

AUTHOR INFORMATION

■

expected to be larger than 4167 cm⁻¹for Eu (⁵D₀), and larger

than 4567 cm⁻¹for Sm (⁴G_5/2). These energy diﬀerence are

suitable for the eﬀective energy transfer from Ln³⁺to the

radical cation of L₁^•+, resulting in luminescence quenching.

The rate constant k_ETof energy transfer for Ln³⁺* → TPA^•+

for complex 1 (8.2 × 10³s⁻¹) is greater than that for 2 (3 ×

10³s⁻¹), and so the luminescence is completely quenched for

1^•+but only partially quenched for 2^•+.

Corresponding Author

Can-Zhong Lu − CAS Key Laboratory of Design and Assembly

of Functional Nanostructures, and Fujian Provincial Key

Laboratory of Nanomaterials, Fujian Institute of Research on

the Structure of Matter, Chinese Academy of Sciences, Fuzhou,

Fujian 350002, People’s Republic of China; Fujian Key

Laboratory of Photoelectric Functional Materials (Huaqiao

University), Xiamen, Fujian 361021, People’s Republic of

China; Xiamen Institute of Rare-earth Materials, Haixi

Institutes, Chinese Academy of Sciences, Xiamen 361021,

People’s Republic of China; orcid.org/0000-0002-8298-

4132; Email: czlu@fjirsm.ac.cn

CONCLUSIONS

■

In summary, we have designed and synthesized the two new

ligands L₁(TPA-bpy) and L₂(TPA-xy-bpy) with a triphenyl-

amine unit as a redox center and bipyridine as a coordination

ligand. The three corresponding lanthanide complexes Eu-

(tta)₃L₁(1), Sm(tta)₃L₁(2), and Eu(tta)₃L₂(3) have been

also synthesized and characterized. The single-crystal struc-

tures of 1 and 2 reveal that Ln³⁺is 8-fold coordinated in a

distorted-trigonal-dodecahedral coordination geometry. De-

tailed photophysical investigations of L₁, L₂, and complexes 1−

3 demonstrate that the emission properties are strongly solvent

dependent. In more polar solvents the complexes mainly show

Ln³⁺4f−4f emissions, whereas in less polar solvents they

exhibit additional ligand-centered luminescence, leading to

white-light emission in some solvents. Biexponential decays are

determined in the solid states, but single-exponential decays

are observed in the investigated solvents for all of the

complexes. The lifetimes of the excited Eu³⁺(⁵D₀) and Sm³⁺

(⁴G_5/2) states in these complexes are all on the microsecond

scale both in the solid state and in solution. A UV/vis/NIR

spectroelectrochemistry study indicates that the complexes

show a new absorption band at 760 nm at an applied potential

of 1.2 V vs Ag⁺/Ag, which is assigned to the absorption of the

radical cation TPA^•+. Complexes 1 and 2 show reversible

luminescence switching properties upon application of an

electrochemical potential, due to the intramolecular energy

transfer from the Eu³⁺or Sm³⁺ions to the electrochemically

generated TPA^•+radical cation. The intramolecular energy

transfer in complexes 1 and 2 and their oxidized forms have

been discussed on the basis of both the experimental results

and the DFT calculations. Our work developed novel single

molecular lanthanide complexes exhibiting white-light emis-

sion in some solvents and electroﬂuorochromic properties,

which may have potential applications for lanthanide sensing,

as well as for photoelectric and biomarker materials.

Authors

Jing Chen − CAS Key Laboratory of Design and Assembly of

Functional Nanostructures, and Fujian Provincial Key

Laboratory of Nanomaterials, Fujian Institute of Research on

the Structure of Matter, Chinese Academy of Sciences, Fuzhou,

Fujian 350002, People’s Republic of China; Fujian Key

Laboratory of Photoelectric Functional Materials (Huaqiao

University), Xiamen, Fujian 361021, People’s Republic of

China; Xiamen Institute of Rare-earth Materials, Haixi

Institutes, Chinese Academy of Sciences, Xiamen 361021,

People’s Republic of China

Ziyu Xie − CAS Key Laboratory of Design and Assembly of

Functional Nanostructures, and Fujian Provincial Key

Laboratory of Nanomaterials, Fujian Institute of Research on

the Structure of Matter, Chinese Academy of Sciences, Fuzhou,

Fujian 350002, People’s Republic of China; Fujian Key

Laboratory of Photoelectric Functional Materials (Huaqiao

University), Xiamen, Fujian 361021, People’s Republic of

China; Xiamen Institute of Rare-earth Materials, Haixi

Institutes, Chinese Academy of Sciences, Xiamen 361021,

People’s Republic of China

Lingyi Meng − CAS Key Laboratory of Design and Assembly of

Functional Nanostructures, and Fujian Provincial Key

Laboratory of Nanomaterials, Fujian Institute of Research on

the Structure of Matter, Chinese Academy of Sciences, Fuzhou,

Fujian 350002, People’s Republic of China; Xiamen Institute of

Rare-earth Materials, Haixi Institutes, Chinese Academy of

Sciences, Xiamen 361021, People’s Republic of China; Fujian

Provincial Key Laboratory of Theoretical and Computational

Chemistry, Xiamen 361005, People’s Republic of China;

orcid.org/0000-0002-8985-5093

Ziying Hu − CAS Key Laboratory of Design and Assembly of

Functional Nanostructures, and Fujian Provincial Key

Laboratory of Nanomaterials, Fujian Institute of Research on

the Structure of Matter, Chinese Academy of Sciences, Fuzhou,

Fujian 350002, People’s Republic of China; Xiamen Institute of

Rare-earth Materials, Haixi Institutes, Chinese Academy of

Sciences, Xiamen 361021, People’s Republic of China; College

of Chemistry, New Campus, Fuzhou University, Fuzhou

350116, People’s Republic of China

ASSOCIATED CONTENT

■

sı

* Supporting Information

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c00392.

Additional synthetic and structural details, crystallo-

graphic data, theoretical calculations, and additional

ﬁgures and tables as described in the text (PDF)

Xiaofei Kuang − CAS Key Laboratory of Design and Assembly

of Functional Nanostructures, and Fujian Provincial Key

Laboratory of Nanomaterials, Fujian Institute of Research on

the Structure of Matter, Chinese Academy of Sciences, Fuzhou,

Fujian 350002, People’s Republic of China; Xiamen Institute of

Rare-earth Materials, Haixi Institutes, Chinese Academy of

Accession Codes

CCDC 1946992 and 1946995−1946996 contain the supple-

mentary crystallographic data for this paper. These data can be

obtained free of charge via www.ccdc.cam.ac.uk/data_request/

cif, or by emailing data_request@ccdc.cam.ac.uk, or by

https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

pubs.acs.org/IC

Article

complex. Angew. Chem., Int. Ed. 2013, 52, 8722−8725. (d) Terai, T.;

Kikuchi, K.; Iwasawa, S.; Kawabe, T.; Hirata, Y.; Urano, Y.; Nagano,

T. Modulation of luminescence intensity of lanthanide complexes by

photoinduced electron transfer and its application to a long-lived

protease probe. J. Am. Chem. Soc. 2006, 128, 6938−6946.

Sciences, Xiamen 361021, People’s Republic of China;

orcid.org/0000-0002-5373-0299

Yiming Xie − Fujian Key Laboratory of Photoelectric Functional

Materials (Huaqiao University), Xiamen, Fujian 361021,

People’s Republic of China

(4) (a) Molloy, J. K.; Jarjayes, O.; Philouze, C.; Fedele, L.; Imbert,

D.; Thomas, F. A redox active switch for lanthanide luminescence in

phenolate complexes. Chem. Commun. 2017, 53, 605−608. (b) Lehr,

J.; Tropiano, M.; Beer, P. D.; Faulkner, S.; Davis, J. J. Reversible redox

modulation of a lanthanide emissive molecular film. Chem. Commun.

2015, 51, 6515−6517. (c) Sato, T.; Higuchi, M. An alternately

introduced heterometallo-supramolecular polymer: synthesis and

solid-state emission switching by electrochemical redox. Chem.

Commun. 2013, 49, 5256−5258. (d) Tropiano, M.; Kilah, N. L.;

Morten, M.; Rahman, H.; Davis, J. J.; Beer, P. D.; Faulkner, S.

Reversible luminescence switching of a redox-active ferrocene −

europium dyad. J. Am. Chem. Soc. 2011, 133, 11847−11849.

(5) (a) Yuasa, J.; Nakagawa, T.; Kita, Y.; Kaito, A.; Kawai, T.

Photoactivatable europium luminescence turn-on by photo-oxygen-

ation of β -diketone having pyrrole rings. Chem. Commun. 2017, 53,

6748−6751. (b) Wang, Z.; Zhang, R.; Ma, Y.; Peng, A.; Fu, H.; Yao, J.

Chemically responsive luminescent switching in transparent flexible

self-supporting [EuW₁₀O₃₆]₉-agarose nanocomposite thin films. J.

Mater. Chem. 2010, 20, 271−277.

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.inorgchem.0c00392

Notes

The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENTS

■

We thank ﬁnancial support from the Strategic Priority

Research Program of the Chinese Academy of Sciences

(XDB20000000), the Key Program of Frontier Science, CAS

(QYZDJ-SSW-SLH033), the National Natural Science Foun-

dation of China (21501175, 51672271, 21701177, 21773246,

21403176, 21875252), the Natural Science Foundation of

Fujian Province (2017J01037, 2019J01123, 2006L2005),

Xiamen Science and Technology Program Project

(3502Z20172029), the Open Project of Fujian Key Laboratory

of Optoelectronic Materials (FJPFM-201601), the grant from

FJIRSM (CXZX-2017-T04), the FJIRSM&IUE Joint Research

Fund (RHZX-2018-002), and the ﬁnancial support from the

Ministry of Human Resources and Social Security of the

People’s Republic of China.

(6) Goulle, V.; Harriman, A.; Lehn, J.-M. An electro-photoswitch:

redox switching of the luminescence of a bipyridine metal complex. J.

Chem. Soc., Chem. Commun. 1993, 1034−1036.

(7) Audebert, P.; Miomandre, F. Electrofluorochromism: from

molecular systems to set-up and display. Chem. Sci. 2013, 4, 575−584.

(8) (a) Bunzli, J.-C. G.; Piguet, C. Taking advantage of luminescent

lanthanide ions. Chem. Soc. Rev. 2005, 34, 1048−1077. (b) Artizzu, F.;

Quochi, F.; Marchio, L.; Figus, C.; Loche, D.; Atzori, M.; Sarritzu, V.;

Kaczmarek, A. M.; Van Deun, R.; Saba, M.; Serpe, A.; Mura, A.;

Mercuri, M. L.; Bongiovanni, G.; Deplano, P. Light conversion

control in NIR-emissive optical materials based on heterolanthanide

Er_xYb_3‑xquinolinolato molecular components. Chem. Mater. 2015, 27,

4082−4092. (c) Sun, L.-N.; Zhang, H.-J.; Fu, L.-Sh.; Liu, F.-Y.; Meng,

Q.-G.; Peng, Ch.-Y.; Yu, J.-B. A new sol-gel material doped with an

erbium complex and its potential optical-amplification application.

Adv. Funct. Mater. 2005, 15, 1041−1048. (d) Van Deun, R.;

Nockemann, P.; Gorller-Walrand, C.; Binnemans, K. Strong erbium

luminescence in the near-infrared telecommunication window. Chem.

Phys. Lett. 2004, 397, 447−450. (e) Hebbink, G. A.; Stouwdam, J. W.;

Rainhoudt, D. N.; Veggel, F. C. J. M. Lanthanide(III)-doped

nanoparticles that emit in the near-infrared. Adv. Mater. 2002, 14,

1147−1150.

REFERENCES

■

(1) (a) Lapaev, D. V.; Nikiforov, V. G.; Safiullin, G. M.; Lobkov, V.

S.; Salikhov, K. M.; Knyazev, A. A.; Galyametdinov, Y. G. Laser

control and temperature switching of luminescence intensity in

photostable transparent film based on terbium(III) β -diketonate

complex. Opt. Mater. 2014, 37, 593−597. (b) Wang, J.; Zhao, W.;

Zhao, M.; Chen, S.; Li, W. Fabrication of thermo-sensitive optical

switches based on lanthanide-polyoxometalates and their “on-off ”

luminescence controlled by temperature. J. Polym. Res. 2016, 23, 76.

(2) (a) Wang, Q. M.; Ogawa, K.; Toma, K.; Tamiaki, H. Smart pH

sensitive luminescent hydrogel based on Eu(III) beta-diketonate

complex and its enhanced photostability. J. Photochem. Photobiol., A

2009, 201, 87−90. (b) Gupta, K.; Patra, A. K. A luminescent pH-

responsive ternary europium(III) complex of beta-diketonates and

terpyridine derivatives as sensitizing antennae - photophysical aspects,

anion sensing, and biological interactions. Eur. J. Inorg. Chem. 2018,

(9) (a) Kuriki, K.; Koike, Y. Plastic optical fiber lasers and amplifiers

containing lanthanide complexes. Chem. Rev. 2002, 102, 2347−2356.

(b) Fernandez-Bravo, A.; Yao, K.; Barnard, E. S.; Borys, N. J.; Levy, E.

S.; Tian, B.; Tajon, C. A.; Moretti, L.; Altoe, M. V.; Aloni, S.;

Beketayev, K.; Scotognella, F.; Cohen, B. E.; Chan, E. M.; Schuck, P.

J. Continuous-wave upconverting nanoparticle microlasers. Nat.

Nanotechnol. 2018, 13, 572−577.

(10) (a) Capecchi, S.; Renault, O.; Moon, D.-G.; Halim, M.;

Etchells, M.; Dobson, P. J.; Salata, O. V.; Christou, V. High-efficiency

organic electroluminescent devices using an organoterbium emitter.

Adv. Mater. 2000, 12, 1591−1594. (b) Zinna, F.; Pasini, M.; Galeotti,

F.; Botta, C.; Bari, L. D.; Giovanella, U. Design of lanthanide-based

OLEDs with remarkable circularly polarized electroluminescence.

Adv. Funct. Mater. 2017, 27, 1603719. (c) Zinna, F.; Giovanella, U.;

Bari, L. D. Highly circularly polarized electroluminescence from a

chiral europium complex. Adv. Mater. 2015, 27, 1791−1795.

(d) Katkova, M. A.; Pushkarev, A. P.; Balashova, T. V.; Konev, A.

N.; Fukin, G. K.; Ketkov, S. Yu.; Bochkarev, M. N. Near-infrared

electroluminescent lanthanide [Pr(III), Nd(III), Ho(III), Er(III),

Tm(III), and Yb(III)] N,O-chelated complexes for organic light-

emitting devices. J. Mater. Chem. 2011, 21, 16611−16620. (e) Biju, S.;

Xu, L.-J.; Sun, Ch.-Zh.; Chen, Zh.-N. White OLEDs based on a novel

Eu^III-tetrakis-β -diketonate doped into 4,4 ′-N,N ′-dicarbazolebiphenyl

1882−1890. (c) Gunnlaugsson, T.; Leonard, J. P.; Senechal, K.;

Harte, A. J. pH Responsive Eu(III)−phenanthroline supramolecular

conjugate: novel “Off −On −Off ” luminescent signaling in the

physiological pH range. J. Am. Chem. Soc. 2003, 125, 12062−12063.

(d) Gunnlaugsson, T.; Leonard, J. P. Lanthanide luminescent

switches: modulation of the luminescence of bis-macrocyclic based

Tb(iii) conjugates in water by H⁺, Na⁺and K⁺. Dalton Trans. 2005,

19, 3204. (e) McCoy, C. P.; Stomeo, F.; Plush, S. E.; Gunnlaugsson,

T. Soft matter pH sensing: from luminescent lanthanide pH switches

in solution to sensing in hydrogels. Chem. Mater. 2006, 18, 4336−

4343. (f) Truman, L. K.; Comby, S.; Gunnlaugsson, T. pH-

Responsive luminescent lanthanide-functionalized gold nanoparticles

with “On-Off ” ytterbium switchable near-infrared emission. Angew.

Chem., Int. Ed. 2012, 51, 9624−9627.

(3) (a) Karbowiak, M.; Cichos, J.; Buczko, K. Interaction of

lanthanide β -diketonate complexes with polyvinylpyrrolidone: proton-

controlled switching of Tb³⁺luminescence. J. Phys. Chem. B 2014,

118, 226−239. (b) Cheng, H.-B.; Hu, G.-F.; Zhang, Z.-H.; Gao, L.;

Gao, X.; Wu, H.-C. Photocontrolled reversible luminescent lanthanide

molecular switch based on a diarylethene −europium dyad. Inorg.

Chem. 2016, 55, 7962−7968. (c) Nakai, H.; Kitagawa, K.; Nakamori,

H.; Tokunaga, T.; Matsumoto, T.; Nozaki, K.; Ogo, S. Reversible

switching of the Luminescence of a photoresponsive gadolinium(III)

https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

pubs.acs.org/IC

Article

as emitting material. J. Mater. Chem. C 2015, 3, 5775−5782.

(f) Kalyakina, A. S.; Utochnikova, V. V.; Zimmer, M.; Dietrich, F.;

Kaczmarek, A. M.; Deun, R. V.; Vashchenko, A. A.; Goloveshkin, A.

tungstophosphate and its electrofluorochromic performance. ACS

Appl. Mater. Interfaces 2016, 8, 11621−11628.

(18) (a) Lian, X.; Zhao, Z.; Cheng, D. Recent progress on

triphenylamine materials: synthesis, properties, and applications. Mol.

Cryst. Liq. Cryst. 2017, 648, 223−235. (b) Wu, J.-T.; Hsiang, T.-L.;

Liou, G.-S. Synthesis and optical properties of redox-active triphenyl-

amine-based derivatives with methoxy protecting groups. J. Mater.

Chem. C 2018, 6, 13345−13351. (c) Lian, X. J.; Zhao, Z.; Cheng, D. J.

Recent progress on triphenylamine materials: synthesis, properties,

and applications. Mol. Cryst. Liq. Cryst. 2017, 648, 223−235. (d) Su,

K.; Sun, N.; Tian, X.; Guo, S.; Yan, Z.; Wang, D.; Chen, C. High-

performance blue fluorescent/electroactive polyamide bearing p-

phenylenediamine and asymmetrical SBF/TPA-based units for

electrochromic and electrofluorochromic multifunctional applications.

J. Mater. Chem. C 2019, 7, 4644−4652. (e) Sun, J.; Liang, Z. Swift

electrofluorochromism of donor-acceptor conjugated polytriphenyl-

amines. ACS Appl. Mater. Interfaces 2016, 8, 18301−18308.

(19) Lin, H.-T.; Huang, C.-L.; Liou, G.-S. Design, synthesis and

electrofluorochromism of new triphenylamine derivatives with AIE-

active pendent groups. ACS Appl. Mater. Interfaces 2019, 11, 11684−

11690.

S.; Nieger, M.; Gerhards, M.; Schepersi, U.; Brase, S. Remarkable high

efficiency of red emitters using Eu(III) ternary complexes. Chem.

Commun. 2018, 54, 5221−5224. (g) He, Y.; Liu, L.; Fu, G.; Li, W.;

Lu, X.; He, H.; Wong, W.-Y. Efficient white polymer light-emitting

diodes (WPLEDs) based on double emitting layers of a PVK: Eu(III)-

complex and Alq₃. J. Mater. Chem. C 2019, 7, 4800−4807.

(11) (a) Harvey, P.; Nonat, A.; Platas-Iglesias, C.; Natrajan, L. S.;

Charbonniere, L. J. Sensing uranyl(VI) ions by coordination and

energy transfer to a luminescent europium(III) complex. Angew.

Chem., Int. Ed. 2018, 57, 9921−9924. (b) Yan, W.; Zhang, Ch.; Chen,

Sh.; Han, L.; Zheng, H. Two lanthanide metal-organic frameworks as

remarkably selective and sensitive bifunctional luminescence sensor

for metal ions and small organic molecules. ACS Appl. Mater.

Interfaces 2017, 9, 1629−1634. (c) Wang, Y.; Xing, Sh.-H.; Bai, F.-Y.;

Xing, Y.-H.; Sun, L.-X. Stable lanthanide −organic framework

materials constructed by a triazolyl carboxylate ligand: multifunction

detection and white luminescence tuning. Inorg. Chem. 2018, 57,

12850−12859. (d) Liu, J.; Ji, G.; Xiao, J.; Liu, Z. Ultrastable 1D

europium complex for simultaneous and quantitative sensing of

Cr(III) and Cr(VI) ions in aqueous solution with high selectivity and

sensitivity. Inorg. Chem. 2017, 56, 4197−4205. (e) Yang, D.; Wang,

Y.; Liu, D.; Li, Zh.; Li, H. Luminescence modulation via cation −p

interaction in a lanthanide assembly: implications for potassium

detection. J. Mater. Chem. C 2018, 6, 1944−1950.

(12) (a) Stochaj, U.; Rodríguez, D. C.; Cooper, D. R.; Kodiha, M.;

Capobianco, J. A. The effects of lanthanide-doped upconverting

nanoparticles on cancer cell biomarkers. Nanoscale 2018, 10, 14464−

14471. (b) Li, Y.; Li, X.; Xue, Zh.; Jiang, M.; Zeng, S.; Hao, J. Second

near-infrared emissive lanthanide complex for fast renal-clearable in

vivo optical bioimaging and tiny tumor detection. Biomaterials 2018,

169, 35−44.

(13) (a) Zhao, L.; Ge, X.; Yan, G.; Wang, X.; Hu, P.; Shi, L.;

Wolfbeis, O. S.; Zhang, H.; Sun, L. Double-mesoporous core −shell

nanosystems based on platinum nanoparticles functionalized with

lanthanide complexes for in vivo magnetic resonance imaging and

photothermal therapy. Nanoscale 2017, 9, 16012−16023. (b) Ge, X.;

Song, Zh.-M.; Su, L.; Yang, Y.-F.; Shi, L.; Si, R.; Ren, W.; Qiu, X.;

Wang, H. Lanthanide (Gd³⁺and Yb³⁺) functionalized gold nano-

particles for in vivo imaging and therapy. Biomaterials 2016, 108, 35−

43.

(14) (a) Vanden Bussche, F.; Kaczmarek, A. M.; Schmidt, J.;

Stevens, C. V.; Van Der Voort, P. Lanthanide grafted phenanthroline-

polymer for physiological temperature range sensing. J. Mater. Chem.

C 2019, 7, 10972−10980. (b) Liu, W.; Chen, C. Y.; Huang, X.; Xie, E.

Q.; Liu, W. S. Functional construction of dual-emitting 4-amino-

naphthalimide encapsulated lanthanide MOFs composite for ratio-

metric temperature sensing. Chem. - Eur. J. 2019, 25, 10054−10058.

J.; Gao, P.; Wu, T.; Gu, X.; Nie, Q.; Wu, D. Tuning the solid-state

white light emission of postsynthetic lanthanide-encapsulated double-

layer MOFs for three-color luminescent thermometry applications.

Inorg. Chem. 2019, 58, 4524−4533.

(15) (a) Di Piazza, E.; Norel, L.; Costuas, K.; Bourdolle, A.; Maury,

O.; Rigaut, S. d −f Heterobimetallic association between ytterbium

and ruthenium carbon-rich complexes: redox commutation of near-IR

luminescence. J. Am. Chem. Soc. 2011, 133, 6174−6176. (b) Norel, L.;

Piazza, E. D.; Feng, M.; Vacher, A.; He, X. Y.; Roisnel, T.; Maury, O.;

Rigaut, S. Lanthanide Sensitization with ruthenium carbon-rich

complexes and redox commutation of near-IR luminescence.

Organometallics 2014, 33, 4824−4835.

(20) Cai, S.; Wang, S.; Wei, D.; Niu, H.; Wang, W.; Bai, X.

Multifunctional polyamides containing pyrrole unit with different

triarylamine units owning electrochromic, electrofluorochromic and

photoelectron conversion properties. J. Electroanal. Chem. 2018, 812,

132−142.

(21) (a) He, G.; Guo, D.; He, C.; Zhang, X.; Zhao, X.; Duan, C. A

Color-tunable europium complex emitting three primary colors and

white light. Angew. Chem., Int. Ed. 2009, 48, 6132−6135. (b) Shelton,

A. H.; Sazanovich, I. V.; Weinstein, J. A.; Ward, M. D. Controllable

three-component luminescence from a 1,8-naphthalimide/Eu(iii)

complex: white light emission from a single molecule. Chem. Commun.

2012, 48, 2749−2751.

(22) Polit, W.; Mucke, P.; Wuttke, E.; Exner, T.; Winter, R. F.

Charge and spin confinement to the amine site in 3-connected

triarylamine vinyl ruthenium conjugates. Organometallics 2013, 32,

5461−5472.

(23) (a) Eliseeva, S. V.; Bunzli, J.-C. G. Lanthanide luminescence for

functional materials and bio-sciences. Chem. Soc. Rev. 2010, 39, 189−

227. (b) Xu, L.-J.; Xu, G.-T.; Chen, Zh.-N. Recent advances in

lanthanide luminescence with metal-organic chromophores as

sensitizers. Coord. Chem. Rev. 2014, 273, 47−62. (c) Woodward, A.

W.; Frazer, A.; Morales, A. R.; Yu, J.; Moore, A. F.; Campiglia, A. D.;

Jucov, E. V.; Timofeeva, T. V.; Belfield, K. D. Lanthanide ion

complexes were prepared with 2PA antenna ligands. Photophysical

characterization suggest the strong potential of the new complexes as

imaging probes. Dalton Trans. 2014, 43, 16626−16639.

(24) (a) Zheng, Y. X.; Lin, J.; Lin, Q.; Yu, Y. N.; Meng, Q. G.; Zhou,

Y. H.; Wang, S. B.; Wang, H. Y.; Zhang, J. A comparative study on the

electroluminescence properties of some terbium β -diketonate

complexes. J. Mater. Chem. 2001, 11, 2615−2619. (b) Biju, S.;

Eom, Y. K.; Bu

nzli, J.-C. G.; Kim, H. K. A new tetrakis ß-diketone

ligand for NIR emitting LnIII ions: luminescent doped PMMA films

and flexible resins for advanced photonic applications. J. Mater. Chem.

C 2013, 1, 6935−6944.

(25) Melby, L. R.; Rose, N. J.; Abramson, E.; Caris, J. C. Synthesis

and fluorescence of some trivalent lanthanide complexes. J. Am. Chem.

Soc. 1964, 86, 5117−5125.

(26) (a) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J.

A. K.; Puschmann, H. OLEX2: A complete structure solution,

refinement and analysis program. J. Appl. Crystallogr. 2009, 42, 339−

341. (b) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr.,

Sect. A: Found. Crystallogr. 2008, 64, 112−122.

(27) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;

Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,

B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.

P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;

Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;

Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;

(16) Yano, M.; Matsuhira, K.; Tatsumi, M.; Kashiwagi, Y.;

Nakamoto, M.; Oyama, M.; Tsukube, H. “ON −OFF ” switching of

europium complex luminescence coupled with a ligand redox process.

Chem. Commun. 2012, 48, 4082−4084.

(17) Gao, W. M.; Yu, T.; Du, Y.; Wang, R. Q.; Wu, L. X.; Bi, L. H.

First orange fluorescence composite film based on Sm-substituted

https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

pubs.acs.org/IC

Article

Montgomery, J. A., Jr.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers,

E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.;

Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.;

Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.;

Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.;

Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;

Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.;

Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas,

(39) (a) Weller, A. Photoinduced electron transfer in solution:

exciplex and radical ion pair formation free enthalpies and their

solvent dependence. Z. Phys. Chem. 1982, 133, 93−98. (b) Kovacs,

D.; Borbas, K. E. The role of photoinduced electron transfer in the

quenching of sensitized Europium emission. Coord. Chem. Rev. 2018,

364, 1−9. (c) Kupryakov, A. S.; Plyusnin, V. F.; Grivin, V. P.; Bryleva,

J. A.; Larionov, S. V. Interligand electron transfer as a reason of very

weak red luminescence of Eu((i -Bu)₂PS₂)₃Phen and Eu-

(C₄H₈NCS₂)₃Phen complexes. J. Lumin. 2016, 176, 130−135.

(40) (a) Indelli, M. T.; Chiorboli, C.; Flamigni, L.; De Cola, L.;

Scandola, F. Photoinduced electron transfer across oligo-p-phenylene

bridges: distance and conformational effects in Ru(II)−Rh(III) dyads.

Inorg. Chem. 2007, 46, 5630−5641. (b) Walther, M. E.; Wenger, O. S.

Energy transfer from rhenium(I) complexes to covalently attached

anthracenes and phenanthrenes. Dalton. Trans. 2008, 6311−6318.

photochemical electron transfer across peptide spacers. J. Phys.

Chem. 1990, 94, 2740−2743.

(41) (a) Crosby, G. A.; Whan, R. E. Selective excitation of trivalent

Tm via intramolecular energy transfer. J. Chem. Phys. 1962, 36, 863.

(b) Crosby, G. A.; Alire, R. M.; Whan, R. E. Intramolecular energy

transfer in rare earth chelates. Role of the triplet state. J. Chem. Phys.

1961, 34, 743−748. (c) Crosby, G. A.; Whan, R. E.; Freeman, J. J.

Spectroscopic studies of rare earth chelates. J. Phys. Chem. 1962, 66,

2493−2499.

(42) Boddula, R.; Singh, K.; Giri, S.; Vaidyanathan, S. Controlled

energy transfer from a ligand to an Eu III ion: a unique strategy to

obtain bright-white-light emission and its versatile applications. Inorg.

Chem. 2017, 56, 10127−10130.

O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian09,

Revision B.01; Gaussian Inc.: Wallingford, CT, 2010.

(28) (a) Stoyanov, S. R.; Villegas, J. M.; Rillema, D. P. Time-

dependent density functional theory study of the spectroscopic

dicarbonyl complex. Inorg. Chem. 2003, 42 (24), 7852−7860.

(b) Salzner, U. Modeling photoelectron spectra of conjugated

oligomers with time-dependent density functional theory. J. Phys.

Chem. A 2010, 114 (41), 10997−11007.

(29) Sonogashira, K.; Tohda, Y.; Hagihara, N. A convenient

synthesis of acetylenes: catalytic substitutions of acetylenic hydrogen

with bromoalkenes, iodoarenes and bromopyridines. Tetrahedron Lett.

1975, 16, 4467−4470.

(30) Ilmi, R.; Khan, M. S.; Li, Zh. Zh.; Zhou, L.; Wong, W.-Y.;

Marken, F.; Raithby, P. R. Utilization of ternary europium complex for

organic electroluminescent devices and as a sensitizer to improve

electroluminescence of red-emitting iridium complex. Inorg. Chem.

2019, 58, 8316−8331.

(31) Shannon, R. D. Revised effective ionic radii and systematic

studies of interatomic distances in halides and chalcogenides. Acta

Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976,

32, 751−767.

(32) Chen, J.; Wenger, O. S. Fluoride binding to an organoboron

wire controls photoinduced electron transfer. Chem. Sci. 2015, 6,

3582−3592.

(33) Sager, W. F.; Filipesc, N.; Serafin, F. A. Substituent effects on

intramolecular energy transfer. I. Absorption and phosphorescence

spectra of rare earth β -diketone chelates. J. Phys. Chem. 1965, 69,

1092−1100.

(34) (a) Reiller, P. E.; Brevet, J. Bi-exponential decay of Eu(III)

complexed by Suwannee River humic substances: Spectroscopic

evidence of two different excited species. Spectrochim. Acta, Part A

2010, 75, 629−636. (b) Fujiwara, M.; Tsukahara, S.; Watarai, H.

Time-resolved total internal reflection fluorometry of ternary

europium(III) complexes formed at the liquid/liquid interface. Phys.

Chem. Chem. Phys. 1999, 1, 2949−2951.

(43) Zhang, J.; Li, H.; Chen, P.; Sun, W.; Gao, T.; Yan, P. A new

strategy for achieving white-light emission of lanthanide complexes:

effective control of energy transfer from blue-emissive fluorophore to

Eu(III) centres. J. Mater. Chem. C 2015, 3, 1799−1806.

(44) Dai, L.; Lo, W.-S.; Gu, Y.; Xiong, Q.; Wong, K.-L.; Kwok, W.-

M.; Wong, W.-T.; Law, G.-L. Breaking the 1,2-HOPO barrier with a

cyclen backbone for more efficient sensitization of Eu(iii)

luminescence and unprecedented two-photon excitation properties.

Chem. Sci. 2019, 10, 4550−4559.

(45) (a) Latva, M.; Takalo, H.; Mukkala, V.-M.; Matachescu, C.;

Rodriguez, J. C.; Kankare, J. Correlation between the lowest triplet

state energy level of the ligand and lanthanide(III) luminescence

quantum yield. J. Lumin. 1997, 75, 149−169. (b) Steemers, F. J.;

Verboom, W.; Reinhoudt, D. N.; Van der Tol, E. B.; Verhoeven, J. W.

New sensitizer-modified calix[4] arenes enabling near-UV excitation

of complexed luminescent lanthanide ions. J. Am. Chem. Soc. 1995,

117, 9408−9414.

(35) (a) Nakamura, K.; Hasegawa, Y.; Kawai, H.; Yasuda, N.;

Tsukahara, Y.; Wada, Y. Improvement of lasing properties of

europium(III) complexes by increase of emission quantum yield.

Thin Solid Films 2008, 516, 2376−2381. (b) Miyata, K.; Nakagawa,

T.; Kawakami, R.; Kita, Y.; Sugimoto, K.; Nakashima, T.; Harada, T.;

Harada, T.; Kawai, T.; Hasegawa, Y. Remarkable luminescence

properties of lanthanide complexes with asymmetric dodecahedron

structures. Chem. - Eur. J. 2011, 17, 521−528.

(46) Shi, M.; Li, F.; Yi, T.; Zhang, D.; Hu, H.; Huang, Ch. Tuning

the triplet energy levels of pyrazolone ligands to match the D₀level

of Europium(III). Inorg. Chem. 2005, 44, 8929−8936.

(47) Luo, Q.-Y.; Luo, H.; Kuang, H.-M.; Chen, W.-T.; Wen, Y.-X. A

novel samarium material: synthesis, structure, photophysical proper-

ties and photoluminescence energy transfer mechanism. J. Solid State

Chem. 2019, 270, 200−204.

(48) Sreenath, K.; Thomas, T. G.; Gopidas, K. R. Cu(II) mediated

generation and spectroscopic study of the tris(4-anisyl)amine radical

cation and dication. Unusually shielded chemical shifts in the dication.

Org. Lett. 2011, 13, 1134−1137.

(36) (a) Kotova, O.; Comby, S.; Lincheneau, C.; Gunnlaugsson, T.

White-light emission from discrete heterometallic lanthanide-directed

self-assembled complexes in solution. Chem. Sci. 2017, 8, 3419−3426.

(b) Zhang, H.; Shan, X.; Zhou, L.; Lin, P.; Li, R.; Ma, E.; Guo, X.; Du,

S. Full-colour fluorescent materials based on mixed-lanthanide(iii)

metal −organic complexes with high-efficiency white light emission. J.

Mater. Chem. C 2013, 1, 888−891. (c) Liao, W.-M.; Li, C.-J.; Wu, X.;

Zhang, J.-H.; Wang, Z.; Wang, H.-P.; Fan, Y.-N.; Pan, M.; Su, C.-Y.

Homometallic Ln(iii)-complexes from an ILCT ligand with sensitized

vis-NIR emission, excitation-dependent PL color tuning and white-

light emission. J. Mater. Chem. C 2018, 6, 3254−3259.

(37) Andrez, J.; Bozoklu, G.; Nocton, G.; Pecaut, J.; Scopelliti, R.;

Dubois, L.; Mazzanti, M. Lanthanide(II) complexes supported by

N,O-donor tripodal ligands: Synthesis, structure, and ligand-depend-

ent redox behavior. Chem. - Eur. J. 2015, 21, 15188−15200.

(38) Morss, L. R. Thermochemical properties of yttrium, lanthanum,

and the lanthanide elements and ions. Chem. Rev. 1976, 76, 827−841.

https://dx.doi.org/10.1021/acs.inorgchem.0c00392

Inorg. Chem. XXXX, XXX, XXX−XXX

Products guided by the article

Product name:bpy-xy-TMS

Cas No:1337570-07-6

R&D Labs maybe for 1337570-07-6

ALPHA PHARMACEUTICAL CO，LTD JIANGSU

Contact:+86-527-84829968,+86-527-84829998

Address:suqian city
Angel Yeast Co., Ltd.

Contact:+86-717-6370352

Address:168 Chengdong Avenue, Yichang, Hubei 443003, P. R.China
Hangzhou Eastbiopharm Co.,Ltd.

Contact:+86-571-88931780

Address:Hangzhou,China
Chongqing Rong＆Quan Pharmaceutical Technology Co. , Ltd.

Contact:86-023-65268721

Address:No. 7, Manshanhong Village, Pingdingshan, Shapingba District, Chongqing Province, China
Wuhan Better Organic Technology Inc.

Contact:13307163183

Address:Wuhan Economic&Technology Development Zone, Hubei

Relevant to this article

Chiral Metallacycles as Catalysts for Asymmetric Conjugate Addition of Styrylboronic Acids to α,β-Enones

Doi:10.1021/jacs.0c01563
(2020)
Doi:10.1021/ja00866a004
(1962)
Doi:10.1021/ja01197a025
(1947)
STEREOSPECIFIC PHOTODIMERIZATION OF UNSATURATED COMPOUNDS INDUCED BY NICKEL COMPLEXES

Doi:10.1246/cl.1985.1235
(1985)
A synthesized GFP analogue emits via a hydrogen-bonding system

Doi:10.1039/b927461h
(2010)
Hydrolytic stability of a phosphate-branched oligonucleotide incorporating a ribonucleoside 3′-phosphotriester unit

Doi:10.1080/15257770500544537
(2006)

Article Doi

Luminescence Tunable Europium and Samarium Complexes: Reversible On/Off Switching and White-Light Emission

DOI: 10.1021/acs.inorgchem.0c00392

Source and publish data:

Authors:

Article abstract of DOI:10.1021/acs.inorgchem.0c00392

Full text of DOI:10.1021/acs.inorgchem.0c00392

Products guided by the article

R&D Labs maybe for 1337570-07-6

Relevant to this article

Hot Product