Manipulating the relaxation pathways of excited states and understanding mechanisms of photochemical reactions present important challenges in chemistry. Here we report a unique zinc(II) complex ...exhibiting unprecedented interplay between the excitation‐wavelength‐dependent emission, thermally activated delayed fluorescence (TADF) and excited state intramolecular proton transfer (ESIPT). The ESIPT process in the complex is favoured by a short intramolecular OH⋅⋅⋅N hydrogen bond. Synergy between the excitation‐wavelength‐dependent emission and ESIPT arises due to heavy zinc atom favouring intersystem crossing (isc). Reverse intersystem crossing (risc) and TADF are favoured by a narrow singlet–triplet gap, ΔEST≈10 kJ mol−1. These results provide the first insight into how a proton‐transfer system can be modified to show a synergy between the excitation‐wavelength‐dependent emission, ESIPT and TADF. This strategy offers new perspectives for designing ESIPT and TADF emitters exhibiting tunable excitation‐wavelength‐dependent luminescence.
Modifying proton‐transfer systems: Incorporating Zn2+ ions in a proton transfer system leads to a very complex interplay between the excited state intramolecular proton transfer (ESIPT), thermally activated delayed fluorescence (TADF) and excitation‐wavelength‐dependent emission.
A new series of luminescent heterometallic europium(III)–lutetium(III) terephthalate metal–organic frameworks, namely (EuxLu1−x)2bdc3·nH2O, was synthesized using a direct reaction in a water ...solution. At the Eu3+ concentration of 1–40 at %, the MOFs were formed as a binary mixture of the (EuxLu1−x)2bdc3 and (EuxLu1−x)2bdc3·4H2O crystalline phases, where the Ln2bdc3·4H2O crystalline phase was enriched by europium(III) ions. At an Eu3+ concentration of more than 40 at %, only one crystalline phase was formed: (EuxLu1−x)2bdc3·4H2O. All MOFs containing Eu3+ exhibited sensitization of bright Eu3+-centered luminescence upon the 280 nm excitation into a 1ππ* excited state of the terephthalate ion. The fine structure of the emission spectra of Eu3+ 5D0-7FJ (J = 0–4) significantly depended on the Eu3+ concentration. The luminescence quantum yield of Eu3+ was significantly larger for Eu-Lu terephthalates containing a low concentration of Eu3+ due to the absence of Eu-Eu energy migration and the presence of the Ln2bdc3 crystalline phase with a significantly smaller nonradiative decay rate compared to the Ln2bdc3·4H2O.
A series of lanthanide(iii) complexes based on the new chiral ligand L, which contains 1,10-phenanthroline and (-)-menthol fragments, namely LnL
(NO
)
(Ln = Eu (1), Gd (2), Tb (3), Dy (4)), have ...been synthesized and structurally characterized. Complexes 1-4 are isostructural and crystallize in the non-centrosymmetric space group P4
2
2. The mononuclear complexes comprise a 10-coordinate Ln
ion with two bidentate N,N-donor ligands (L) and three bidentate chelating nitrate groups. The magnetic properties of complexes 1-4 are determined mainly by the Ln
ions. In the case of complexes 3 and 4, significant anisotropy results in nonlinear field dependences of magnetization at low temperature. Complexes 1, 3 and 4 exhibit metal-centered red (Eu
), green (Tb
) and yellow (Dy
) luminescence, respectively, whereas complex 2 displays blue ligand-based luminescence in the solid state at room temperature. The luminescence quantum yield for the solid samples increases in the order 4 < 2 ≈ 3 < 1. The europium(iii) complex shows long luminescence lifetimes (up to 1750 μs) and a very high quantum yield (φ
= 0.87); these make this compound promising for application in sensing and optoelectronics.
A series of mononuclear heteroleptic copper(I) halide complexes, CuL(PPh3)X (X = Cl, Br, I), based on 4-(3,5-diphenyl-1H-pyrazol-1-yl)-6-(piperidin-1-yl)pyrimidine (L) and triphenylphosphine, have ...been synthesized by reaction between CuX (X = Cl, Br, I), L and PPh3 in a molar ratio of 1/1/1 in MeCN solutions. The copper atom, showing the distorted tetrahedral environment, is bound by the N,N-chelating ligand L, triphenylphosphine and a halide ion. The complexes CuL(PPh3)Cl and CuL(PPh3)Br are isostructural. In CH2Cl2 solutions, L and the complexes CuL(PPh3)X (X = Cl, Br, I) display a luminescence band with λ(max) = 377 nm and a lifetime of 1.9 ns (ligand-based luminescence (LL*)). However, the complex CuL(PPh3)I has an additional weak luminescence band with λ(max) = 681 nm and a lifetime of 96 ns of (3)MLCT origin. In the solid state, L shows the splitting of the luminescence band to λ(max) = 365 and 384 nm and a slight increase of the lifetime to 2.66 ns. Solid samples of the complexes CuL(PPh3)X demonstrate (3)MLCT luminescence bands at 620 nm (X = Cl), 605 nm (X = Br) and 559 nm (X = I) with lifetimes in the range 3.6-11.2 μs, whereas the LL* band (377 nm) is absent. Quantum yields and rate constants of radiative and nonradiative processes were determined in CH2Cl2 solutions and in the solid state for all complexes. The luminescence quantum yield and lifetimes for the solid samples increase in the order CuL(PPh3)Cl < CuL(PPh3)Br < CuL(PPh3)I. This is due to the increase of radiative decay and simultaneous suppression of nonradiative decay. The complex CuL(PPh3)I shows a high quantum yield of 29.4% and an excited state lifetime of 11.2 μs.
Transient absorption and time resolved luminescence spectroscopy were used to study photophysical processes in the macrocycle-appended 1,8-naphthalimide compound H
3
L, and its Eu(
iii
) and Gd(
iii
...) complexes Eu·L and Gd·L, in particular the naphthalimide-Eu(
iii
) energy-transfer process. In all cases aggregation of the naphthalimide chromophores results in a low-energy emission feature in the 470–500 nm region in addition to the naphthalimide fluorescence; this lower-energy emission has a lifetime longer by an order of magnitude than the monomer naphthalimide fluorescence. Transient absorption spectroscopy was used to measure the decay of the naphthalimide triplet excited state, which occurs in the range 30–50 μs. In Eu·L, partial energy-transfer from the naphthalimide chromophore results in sensitized Eu(
iii
)-based emission in addition to the naphthalimide-based fluorescence features. Time-resolved measurements on the sensitized Eu(
iii
)-based emission reveal both fast (~10
9
s
−1
) and slow (~10
4
s
−1
) energy-transfer processes from the naphthalimide energy-donor, which we ascribe to energy-transfer occurring from the singlet and triplet excited state of naphthalimide respectively. This is an unusual case of observation of sensitization of Eu(
iii
)-based emission from the singlet state of an aromatic chromophore.
A new series of luminescent heterometallic europium(III)–lutetium(III) terephthalate metal–organic frameworks, namely (Eusub.x Lusub.1−x )sub.2 bdcsub.3 ·nHsub.2 O, was synthesized using a direct ...reaction in a water solution. At the Eusup.3+ concentration of 1–40 at %, the MOFs were formed as a binary mixture of the (Eusub.x Lusub.1−x )sub.2 bdcsub.3 and (Eusub.x Lusub.1−x )sub.2 bdcsub.3 ·4Hsub.2 O crystalline phases, where the Lnsub.2 bdcsub.3 ·4Hsub.2 O crystalline phase was enriched by europium(III) ions. At an Eusup.3+ concentration of more than 40 at %, only one crystalline phase was formed: (Eusub.x Lusub.1−x )sub.2 bdcsub.3 ·4Hsub.2 O. All MOFs containing Eusup.3+ exhibited sensitization of bright Eusup.3+ -centered luminescence upon the 280 nm excitation into a sup.1 ππ* excited state of the terephthalate ion. The fine structure of the emission spectra of Eusup.3+ 5 Dsub.0 -sup.7 Fsub.J (J = 0–4) significantly depended on the Eusup.3+ concentration. The luminescence quantum yield of Eusup.3+ was significantly larger for Eu-Lu terephthalates containing a low concentration of Eusup.3+ due to the absence of Eu-Eu energy migration and the presence of the Lnsub.2 bdcsub.3 crystalline phase with a significantly smaller nonradiative decay rate compared to the Lnsub.2 bdcsub.3 ·4Hsub.2 O.
Nanosecond laser flash photolysis and time resolved luminescence were used to study the photophysical processes for Eu((i-Bu)2PS2)3Phen (1) and Eu(C4H8NCS2)3Phen (2) complexes in acetonitrile. These ...complexes show a very weak red Eu3+ luminescence in spite of the fact that the phenanthroline molecule in triplet state is a good antenna to excite the red luminescence of many Eu(III)-Phen complexes. To determine the reasons of this effect the photoprocesses in solutions, containing the (i-Bu)2PS2− or C4H8NCS2− ions and free phenanthroline molecule, have been studied with the use of laser flash photolysis (266nm). It was shown that the phenanthroline in triplet excited state (TPhen*) deprives the electron from these dithiolate ions with a high rate constants close to 109M−1s−1. The transient spectra of phenanthroline anion-radical and dithiolate radicals were recorded which are in a good agreement with literature data. Since the effective concentration of dithiolate ions (L−) in the coordination sphere of 1 and 2 complexes is close to 10M the time of electron transfer between L− and TPhen* is in the range of 100ps or less. As the laser flash photolysis of solutions of 1 and 2 complexes with a 10ns time resolution failed to detect the spectra of phenanthroline anion-radical and dithiolate radicals, it indicates that the time of back electron transfer is less than 10−8s. Thus, the very weak red luminescence of 1 and 2 complexes is due to the electron transfer between ligands in the coordination sphere which successfully suppresses the energy transfer from the phenanthroline triplet state to Eu3+ ion.
•The rate constants of electron transfer from dithiolate anions (L−) to Phen molecule in triplet state (TPhen*) are close to diffusion limit.•High local concentration of L− ions in coordination sphere of EuL3Phen complex leads to fast electron transfer between L− and TPhen*.•This process suppresses the energy transfer and red Eu3+ luminescence.
Time resolved luminescence, nanosecond laser flash photolysis, and quantum chemical calculations were used to study the photophysical processes for new chiral ligand (L) containing phenanthroline ...(Phen) and menthol moiety and EuL2(NO3)3 and TbL2(NO3)3 complexes. The absorption and luminescence spectra of free L in acetonitrile are shifted to the red at 10 nm with respect to Phen. The lifetime and quantum yield of luminescence of L are significantly increased (τ = 2.5 ns φf = 0.059) as compared with Phen (τ = 0.51 ns φf = 0.0087 1). As a result of intersystem crossing (ISC) ligand L goes to the triplet state (quantum yield φT = 0.092). The triplet-triplet absorption spectrum of L is a broad band with maximum at 450 nm. The protonation of L leads to the appearance of LH+ form which has a broad luminescence band with a maximum at 482 nm and a lifetime of 38 ns. The EuL2(NO3)3 complex exists in solution at a high concentration and exhibits a characteristic red luminescence. However, as the concentration of EuL2(NO3)3 decreases, the complex dissociates and the bands of free L ligand and protonated LH+ form appear in the absorption and luminescence spectra. Quantum-chemical calculations allow to calculate the geometry and absorption spectra of free and protonated ligands and EuL2(NO3)3 complex.
Display omitted
•The photophysical parameters were determined for new chiral L ligand and its protonated LH+ form in acetonitrile. The luminescence spectra and kinetics of EuL2(NO3)3 and TbL2(NO3)3 complexes were established. The quantum-chemical calculations of geomery and absorption spectra of Phen, L, LH+ and EuL2(NO3)3 have been carried out.
A series of lanthanide(
iii
) complexes based on the new chiral ligand L, which contains 1,10-phenanthroline and (-)-menthol fragments, namely LnL
2
(NO
3
)
3
(Ln = Eu (
1
), Gd (
2
), Tb (
3
), Dy ...(
4
)), have been synthesized and structurally characterized. Complexes
1-4
are isostructural and crystallize in the non-centrosymmetric space group
P
4
1
2
1
2. The mononuclear complexes comprise a 10-coordinate Ln
3+
ion with two bidentate N,N-donor ligands (L) and three bidentate chelating nitrate groups. The magnetic properties of complexes
1-4
are determined mainly by the Ln
3+
ions. In the case of complexes
3
and
4
, significant anisotropy results in nonlinear field dependences of magnetization at low temperature. Complexes
1
,
3
and
4
exhibit metal-centered red (Eu
3+
), green (Tb
3+
) and yellow (Dy
3+
) luminescence, respectively, whereas complex
2
displays blue ligand-based luminescence in the solid state at room temperature. The luminescence quantum yield for the solid samples increases in the order
4
<
2
3
<
1
. The europium(
iii
) complex shows long luminescence lifetimes (up to 1750 μs) and a very high quantum yield (
f
= 0.87); these make this compound promising for application in sensing and optoelectronics.
Novel chiral luminescent Ln(
iii
) complexes are reported.
A series of mononuclear heteroleptic copper(
i
) halide complexes, CuL(PPh
3
)X (X = Cl, Br, I), based on 4-(3,5-diphenyl-1
H
-pyrazol-1-yl)-6-(piperidin-1-yl)pyrimidine (L) and triphenylphosphine, ...have been synthesized by reaction between CuX (X = Cl, Br, I), L and PPh
3
in a molar ratio of 1/1/1 in MeCN solutions. The copper atom, showing the distorted tetrahedral environment, is bound by the
N
,
N
-chelating ligand L, triphenylphosphine and a halide ion. The complexes CuL(PPh
3
)Cl and CuL(PPh
3
)Br are isostructural. In CH
2
Cl
2
solutions, L and the complexes CuL(PPh
3
)X (X = Cl, Br, I) display a luminescence band with
λ
max
= 377 nm and a lifetime of 1.9 ns (ligand-based luminescence (LL*)). However, the complex CuL(PPh
3
)I has an additional weak luminescence band with
λ
max
= 681 nm and a lifetime of 96 ns of
3
MLCT origin. In the solid state, L shows the splitting of the luminescence band to
λ
max
= 365 and 384 nm and a slight increase of the lifetime to 2.66 ns. Solid samples of the complexes CuL(PPh
3
)X demonstrate
3
MLCT luminescence bands at 620 nm (X = Cl), 605 nm (X = Br) and 559 nm (X = I) with lifetimes in the range 3.6-11.2 μs, whereas the LL* band (377 nm) is absent. Quantum yields and rate constants of radiative and nonradiative processes were determined in CH
2
Cl
2
solutions and in the solid state for all complexes. The luminescence quantum yield and lifetimes for the solid samples increase in the order CuL(PPh
3
)Cl < CuL(PPh
3
)Br < CuL(PPh
3
)I. This is due to the increase of radiative decay and simultaneous suppression of nonradiative decay. The complex CuL(PPh
3
)I shows a high quantum yield of 29.4% and an excited state lifetime of 11.2 μs.
Correlations between spectral properties and structural parameters are discussed.
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