Carbazole effect on ground- And excited-state properties of rhenium(i) carbonyl complexes with extendedterpy-like ligands

Article abstract of DOI:10.1039/d0dt04340k

The ground- and excited-state properties of three novel complexes [ReCl(CO)₃(Lⁿ-κ²N)] bearing 2,2′:6′,2′′-terpyridine, 2,6-di(thiazol-2-yl)pyridine and 2,6-di(pyrazin-2-yl)pyridine functionalized with 9-carbazole attached to the central pyridine ring of the triimine coreviaphenylene linkage were investigated by spectroscopic and electrochemical methods and were simulated using density functional theory (DFT) and time-dependent DFT. To get a deeper and broader understanding of structure-property relationships, the designed Re(i) carbonyl complexes were compared with previously reported analogous systems - without any groups attached to the phenyl ring and bearing pyrrolidine instead of 9-carbazole. The results indicated that attachment of theN-carbazolyl substituent to the triimine core has less influence on the nature of the triplet excited state of [ReCl(CO)₃(Lⁿ-κ²N)] than the pyrrolidine group. Additionally, the impact of the ligand structural modifications on the light emission of the Re(i) complexes under external voltage was preliminarily examined with electroluminescence spectra of diodes containing the synthesized new molecules in an active layer.

Full text of DOI:10.1039/d0dt04340k

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Carbazole effect on ground- and excited-state
properties of rhenium(I) carbonyl complexes
with extended terpy-like ligands†
Cite this: Dalton Trans., 2021, 50,
3943
a
Katarzyna Choroba,a Anna Maroń, a Anna Świtlicka, a Agata Szłapa-Kula,
Mariola Siwy,b Justyna Grzelak,c Sebastian Maćkowski, c Tomasz Pedzinski,d
Ewa Schab-Balcerzak*a,b and Barbara Machura
*
a
The ground- and excited-state properties of three novel complexes [ReCl(CO)3(Ln-κ2N)] bearing
2,2’:6’,2’’-terpyridine, 2,6-di(thiazol-2-yl)pyridine and 2,6-di(pyrazin-2-yl)pyridine functionalized with
9-carbazole attached to the central pyridine ring of the triimine core via phenylene linkage were investi-
gated by spectroscopic and electrochemical methods and were simulated using density functional theory
(DFT) and time-dependent DFT. To get a deeper and broader understanding of structure–property
relationships, the designed Re(I) carbonyl complexes were compared with previously reported analogous
systems – without any groups attached to the phenyl ring and bearing pyrrolidine instead of 9-carbazole.
The results indicated that attachment of the N-carbazolyl substituent to the triimine core has less
influence on the nature of the triplet excited state of [ReCl(CO)3(Ln-κ2N)] than the pyrrolidine group.
Additionally, the impact of the ligand structural modifications on the light emission of the Re(I) complexes
under external voltage was preliminarily examined with electroluminescence spectra of diodes containing
the synthesized new molecules in an active layer.
Received 22nd December 2020,
Accepted 12th February 2021
DOI: 10.1039/d0dt04340k
rsc.li/dalton
modulated by the environment. In contrast to polypyridine
complexes of other transition ions, the complexes fac-[ReX
Introduction
Rhenium(I) carbonyl-diamine complexes, reported for the first (CO)3(N∩N)] contain a single electron-accepting R-diimine
time by Wrighton and Morse in 1974,1 have been widely inves- ligand (N∩N), which allows to avoid the problem of excited-
tigated mostly due to their importance for potential appli- electron localization. The carbonyl ligands of fac-[ReX
cations in catalysis, bioimaging, organic light-emitting diodes, (CO)3(N∩N)] act as IR markers of redistribution of electron
and solar energy conversion.2–27 These compounds have also density upon excitation, while information on the N∩N•−
been found to be well suited for fundamental studies of photo- ligand is manifested in the UV-Vis spectral region of the tran-
induced processes in transition metal complexes. The charac- sition absorption spectra. Therefore, excited-state dynamics of
ter of the excited states and thus the photophysical and photo- [ReX(CO)3(N∩N)] can be successfully examined using ultrafast
chemical properties of these systems can be broadly tuned by experimental methods such as time-resolved infrared spec-
structural variations of diamine and ancillary ligands and troscopy, fluorescence up-conversion methods, time-resolved
emission spectroscopy, and transient absorption.28–34 For [ReX
(CO)3(bipy)] and [ReX(CO)3(phen)], it was found that the opti-
1
aInstitute of Chemistry, University of Silesia, 9th Szkolna St., 40-006 Katowice,
Poland. E-mail: barbara.machura@us.edu.pl
cally populated MLCT state undergoes femtosecond intersys-
tem crossing (ISC) forming two triplet states: diimine-localized
ππ* intraligand (3IL) and vibrationally hot {ReCl(CO)3} → bpy
bCentre of Polymer and Carbon Materials, Polish Academy of Sciences,
34th M. Curie-Sklodowska St., 41-819 Zabrze, Poland
3
3
3
of MLCT character. The conversion from IL to MLCT occurs
on a picosecond time scale, and the formed relaxed 3MLCT
state decays by minor radiative and major nonradiative path-
ways to the ground state.28,35,36
cInstitute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus
Copernicus University, 5th Grudziadzka St., 87-100 Torun, Poland
dFaculty of Chemistry, Adam Mickiewicz University in Poznań, 89b Umultowska,
61-614 Poznań, Poland
†Electronic supplementary information (ESI) available: Identification, X-Ray ana-
lysis, frontier molecular orbital analysis, electrochemistry, absorption spectra
and TD-DFT calculations, emission properties, nano- and femtosecond transient
absorption, singlet oxygen generation and proposed energy diagrams. CCDC
2044804. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/d0dt04340k
By introduction of suitable substituents into the diamine
core or alteration of the ancillary ligands (X), the nature and
energy of the excited states in these systems can be changed. It
is possible that LLCT (ligand-to-ligand-charge-transfer), IL
(intraligand), and ILCT (intraligand-charge-transfer) excited
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states would be responsible for the photoluminescence of Aldrich), poly(3,4-(ethylenedioxy)thiophene):poly-(styrenesulfo-
rhenium(I) carbonyl-diamine complexes.37–45 nate) PEDOT:PSS (0.1–1.0 S cm−1) and substrates with pixilated
In recent years, particular attention has been paid to ITO anodes (Ossila), as well as all solvents for synthesis (of
rhenium(I) carbonyl complexes bearing a diimine ligand of reagent grade) and for spectroscopic studies (of HPLC grade)
D–A or D–π-A type, which gives rise to ILCT transitions originat- were all commercially available and used without further puri-
ing from the donor orbital localized on the electron-rich group fication. The films and blends with PVK:PBD (50:50 wt%) on
to the diimine-based π*acceptor orbital and co-occurring with glass substrates as well as all the devices with the following
the metal-to-ligand charge transfer (MLCT) excitation in the configurations: ITO:PEDOT:PSS/compound/Al and ITO:PEDOT:
visible region. Most importantly, these systems were found to PSS/PVK:PBD:compound/Al with 15, 2 and 1 wt% complex
exhibit enhanced photo- and electro-luminescence properties content in the blend, were prepared according to the method
relative to unsubstituted (parent) compounds. Generally, it is reported in our previous work.63–66,76,77 The ligands L1–L3 were
attributed to a thermal equilibrium between energetically prepared according to the modified method reported in our
close excited states 3MLCT and 3ILCT/3IL.46–62
previous studies,66,77,78–80 and detailed synthetic procedures
Continuing our research on the photophysical properties of are provided in the ESI.
rhenium(I) carbonyl complexes with terpy-like ligands,63–69 we
Preparation of [ReCl(CO)3(Ln-κ2N)] (1–3)
present here three novel complexes [ReCl(CO)3(Ln-κ2N)]
bearing 2,2′:6′,2′′-terpyridine (terpy), 2,6-di(thiazol-2-yl)pyri- Re(I) carbonyl complexes were prepared using [Re(CO)5Cl]
dine (dtpy) and 2,6-di(pyrazin-2-yl)pyridine (dppy) functiona- (0.10 g, 0.27 mmol) and a suitable Ln ligand (0.27 mmol)
lized with a 9-carbazole unit, attached to the central pyridine according to the procedure given in our previous work.68
ring of the triimine core via a phenylene linkage (Scheme 1).
Argon-saturated acetonitrile solution of a suitable ligand and
Carbazole, consisting of two benzene rings fused on either pentacarbonyl chlororhenium was heated in an autoclave
side of a pyrrolidine ring, is a molecular block of outstanding reactor for 20 h at 150 °C and gradually cooled to room temp-
importance in organic materials due to strong electron donating erature for 30 h to induce crystallization. The synthesis
properties and excellent hole-transporting abilities.70–75 The resulted in yellow (1) and orange (2, 3) solids (with crystals
ground- and excited-state properties of 1–3 were investigated by suitable for X-ray diffraction analysis in the case of 2), washed
spectroscopic and electrochemical methods, as well as simu- with chloroform or diethyl ether and air dried.
lated by density functional theory (DFT) and time-dependent
1. Yield: 70%. IR (KBr, cm−1): 2021(vs), 1917(vs) and 1889(vs)
DFT. To gain a better understanding of structure–property ν(CuO); 1603(m), 1520(w) ν(CvN) and ν(CvC). NMR: 1H NMR
relationships in these systems, optical and electrochemical pro- (400 MHz, DMSO-d6) δ 9.24 (s, 1H, HB4), 9.16 (d, J = 8.2 Hz, 1H,
perties of 1–3 were analyzed in comparison to previously
H
E4), 9.09 (d, J = 5.2 Hz, 1H, HE1), 8.82 (d, J = 4.3 Hz, 1H, HA1),
reported systems – without any groups attached to the phenyl 8.52 (d, J = 8.5 Hz, 2H, HC2), 8.42 (t, J = 7.4 Hz, 1H, HE3), 8.33 (s,
ring (1A–3A) and bearing pyrrolidine instead of carbazole (1B– 1H, HB2), 8.28 (d, J = 7.8 Hz, 2H, HD5), 8.08 (t, J = 7.1 Hz, 1H,
3B) (Scheme S1†).66 Identification of structure–property corre-
H
A3), 7.96 (d, J = 7.7 Hz, 1H, HA4), 7.91 (d, J = 8.5 Hz, 2H, HC3),
lations is of high importance for the rational design of new light 7.80 (t, 1H, HE2), 7.65 (t, 1H, HA2), 7.53–7.44 (m, 4H, HD2,D3),
emitting materials with the excited state dynamics for desirable 7.33 (t, J = 7.8 Hz, 2H, HD4). 13C NMR (100 MHz, DMSO-d6)
photophysical properties and technological applications.
δ 197.8, 194.5, 191.0 (3CO), 161.5 (CB1), 157.8 (CA5), 157.2 (CB5),
156.3 (CE5), 152.7 (CE1), 149.7 (CC4), 149.2 (CA1), 139.9 (CE3),
139.8 (CD1), 139.2 (CC1), 136.9 (CA3), 133.6 (CB3), 129.8 (CC2),
127.5 (CE2), 127.1 (CC3), 126.4 (CD3), 125.5 (CA2), 125.2 (CE4),
125.0 (CB2), 124.4 (CA4), 123.0 (CD6), 120.7 (CB4), 120.6 (CD4),
120.4 (CD5), 109.7 (CD2). Anal. calc. for Re(CO)3Cl(N4C33H22)
(780.24 g mol−1): C 55.42; H 2.84; N 7.18% found: C 55.74;
H 2.866; N 7.22%. DSC: I run Tm = 216 °C; II run Tg = 205 °C.
2. Yield: 75%. IR (KBr, cm−1): 2021(vs), 1920(vs) and 1895
(vs) ν(CuO); 1600(s) and 1522(w) ν(CvN) and ν(CvC). NMR:
1H NMR (400 MHz, acetone-d6) δ 9.01 (s, 1H), 8.51 (d, J = 8.6
Hz, 2H), 8.44–8.39 (m, 2H), 8.31–8.24 (m, 3H), 8.18 (d, J = 3.2
Hz, 1H), 8.11 (d, J = 3.1 Hz, 1H), 7.95 (d, J = 8.6 Hz, 2H), 7.56
(d, J = 8.2 Hz, 2H), 7.49 (t, J = 7.7 Hz, 2H), 7.35 (t, J = 7.4 Hz,
2H). 13C NMR not recorded due to insufficient complex solubi-
lity. Anal. calc. for [Re(CO)3Cl(N4S2C29H18)]·12(CH3CN) (813.05 g
mol−1): C 48.76; H 2.42; N 7.75; S 7.89% found: C 49.11; H
2.557; N 7.35; S 7.783%. DSC: I run Tm = 210, 233 261 °C; II
run Tg = 208 °C.
Experimental section
Materials
Pentacarbonyl chlororhenium [Re(CO)5Cl] (Sigma Aldrich),
poly(9-vinylcarbazole) PVK (Mn
=
25 000–50 000; Sigma
3. Yield: 65%. IR (KBr, cm−1): 2023(vs), 1927(s) and 1907(vs)
1
Scheme 1 Re(I) complexes studied in the current work.
3944 | Dalton Trans., 2021, 50, 3943–3958
ν(CuO); 1603(s), 1521(w) ν(CvN) and ν(CvC). NMR: H NMR
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Table 1 Crystal data and structure refinement for 2
(400 MHz, DMSO-d6) δ 10.41 (s, 1H), 9.49 (s, 1H), 9.21 (s, 1H),
9.17 (d, J = 2.2 Hz, 1H), 9.01 (d, J = 2.8 Hz, 1H), 8.95 (s, 2H),
8.60–8.54 (m, 3H), 8.29 (d, J = 7.9 Hz, 2H), 7.95 (d, J = 8.4 Hz,
2H), 7.55–7.46 (m, 4H), 7.35 (t, J = 7.2 Hz, 2H) 13C NMR
(125 MHz, DMSO-d6) δ 196.60, 194.68, 189.61 (3CO), 158.88,
155.70, 153.52, 151.03, 150.14, 148.02, 147.21, 145.92, 145.41,
144.18, 139.80, 139.60, 133.21, 130.04, 127.28, 126.54, 125.66,
123.13, 121.87, 120.74, 120.58, 109.79, 79.19. Anal. calc. for [Re
2
Empirical formula
Formula weight
T, K
Wavelength, Å
Crystal system
Space group
Unit cell dimensions, Å and °
a
C32H18ClN4O3ReS2
792.27
295.0(2)
0.71073
Monoclinic
P21/c
(CO)3Cl(N6C31H20)]·1(CHCl3) (841.91 g mol−1): C 49.22; H 2.45;
2
11.5309(5)
19.4727(7)
14.6172(5
106.870(4)
3140.9(2)
4
1.675
4.126
1544
0.18 × 0.14 × 0.09
3.39 to 25.05
−13 ≤ h ≤ 13
−23 ≤ k ≤ 18
−17 ≤ l ≤ 13
13 122
5538 [Rint = 0.0244]
99.7
0.792 and 1.000
5538/0/388
1.058
N 9.98% found: C 49.63; H 2.449; N 10.09%. DSC: I run Tm
=
b
c
257, 261 °C with decomposition.
β
V, Å3
Crystal structure determination and refinement
Z
Dc, g cm−3
The X-ray diffraction data for 2 were collected using an Oxford
Diffraction four-circle diffractometer Gemini A Ultra with an
Atlas CCD detector using graphite monochromated MoKα radi-
ation (λ = 0.71073 Å) at room temperature. Diffraction data col-
lection, cell refinement and data reduction were performed
using CrysAlisPro software.81 The structure was solved using
direct methods in SHELXS and refined by full-matrix least-
squares on F2 using SHELXL-2014.82 All the non-hydrogen
atoms were refined anisotropically, and hydrogen atoms were
placed at calculated positions and refined with riding con-
strains: d(C–H) = 0.93 Å, Uiso(H) = 1.2Ueq(C). Details of the crys-
tallographic data collection, structural determination, and
refinement for 2 are given in Table 1 whereas selected bond
lengths and angles in comparison with those calculated for 1
and 3 are listed in Table S1, ESI.†
Absorption coefficient, mm−1
F(000)
Crystal size, mm
θ range for data collection, °
Index ranges
Reflections collected
Independent reflections
Completeness to 2θ
Min. and max. transm.
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
R1
0.0255
0.0554
wR2
R indices (all data)
R1
0.0347
0.0579
0.753 and −0.460
2044804
wR2
Largest diff. peak and hole, e Å−3
CCDC number
Crystallographic data for
2 were deposited with the
Cambridge Crystallographic Data Center, CCDC 2044804.†
Physical measurements
0.1 V s−1 and 0.01 V s−1, respectively. The solution was purged
with argon for about 10 min before every measurement. All the
results were calibrated on ferrocene (Fc) (internal standard).
Differential scanning calorimetry studies were carried out
with the use of TA-DSC 2010 apparatus under a nitrogen atmo-
The IR spectra were measured using a Nicolet iS5 FTIR spectro-
photometer (4000–400 cm−1) in the form of KBr pellets.
The absorption spectra were measured using Thermo
Scientific Evolution 220 (solution) and Jasco V570 (solid state
as film deposited on a glass substrate and as blends with poly
(N-vinylcarbazole) (PVK): 2-(4-tert-butylphenyl)-5-(4-biphen-
ylyl)-1,3,4-oxadiazole (PBD) on a glass substrate).
sphere, with a heating rate of 20 °C min−1
.
Photoluminescence spectra
The NMR spectra were collected (295 K) on a Bruker Avance
400 NMR spectrometer or Bruker Avance 500 NMR spectro- The emission spectra of samples in the solid state (as powder)
meter in dimethyl sulfoxide-d6 for 1 and 3 and in acetone-d6 and solution were measured on a FLS-980 fluorescence
for 2. For L1 and 1, multidimensional correlation NMR was spectrophotometer. The emission spectra at 77
K were
performed with homonuclear correlation spectroscopy per- measured in an ethanol : methanol (4 : 1 v/v) matrix frozen
formed using 2D COSY experiments, while heteronuclear cor- with liquid nitrogen. The time-resolved TCSPC measurements
relation spectroscopy was done on the basis of HMQC or were carried out for optically diluted solutions using pico-
HMBC (long-range) experiments.
second pulsed diodes (EPLED 375 nm, EPLED 405 nm) as exci-
Electrochemical measurements were performed with an tation light sources and PMT (Hamamatsu, R928P, Japan) as a
Eco Chemie Autolab PGSTAT128n potentiostat. The measure- detector, with additional measurement of the IRF for the ana-
ments were investigated in acetonitrile solution (Sigma- lysis of a fluorescence decay. The quantum yield of each
Aldrich, HPLC, ≥99.8%, c = 10−3 mol L−1) using a platinum complex was measured on FLS-980 with the integrating sphere
electrode (diam. 2.0 mm) as the working electrode and 0.1 M attached. The measurements were taken using direct methods
Bu4NPF6 (Sigma-Aldrich, 99%) as the electrolyte. Platinum coil for argon-saturated solutions and powdered samples, with
and silver wire were used as auxiliary and reference electrode. their respective solvents or Spectralon® standard as the refer-
Cyclic voltammetry (CV) and differential pulse voltammetry ence. The samples were excited at their first excitation maxima
(DPV) were recorded with moderate scan rates equal to and measured with 0.25 nm scan rate, 0.2 dwell time, and 3
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scan repetitions. FLS-980 software was used to perform the Xplorer (Ultrafast Systems) software, with corrections for the
emission correction and calculation of the quantum yield. probe chirp and solvent signal before each analysis. The soft-
Photoluminescence spectra in the solid state as film and as ware allowed to perform Singular Value Deconvolution of the
blends with poly(N-vinylcarbazole) (PVK):2-(4-tert-butylphenyl)- 3D surface into principal components (spectra and kinetics),
5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) deposited on a glass Global Analysis (lifetimes, with an error of ∼10%), and Decay
substrate were collected on a Hitachi F-2500 spectrometer. A Associated Spectra, DAS, of the detected transients.
precise voltage supply (Gw Instek PSP-405) with the sample
Computational details
fixed to an XYZ stage was applied to collect electrolumines-
cence (EL) spectra, and all the measurements were performed
using the procedure reported in our previous work.76
The theoretical calculations for geometry optimization, mole-
cular orbital analysis, absorption spectra, ionization poten-
tials, electronic affinities, and reorganization energies were
performed using the GAUSSIAN-09 program package86 at the
DFT or TD-DFT level with the PBE1PBE87,88 hybrid exchange–
correlation functional, and the def2-TZVPD basis set for
rhenium and def2-TZVP basis set for other elements89–91 with
a polarizable continuum model (PCM) and acetonitrile as the
solvent.92–94 After optimization of the geometry, vibrational fre-
quencies were calculated to verify the minimum on the poten-
tial energy surface.
Singlet oxygen sensitization
The singlet oxygen emission was measured on a FluoTime 300
fluorescence spectrophotometer (PicoQuant, Germany) with a
NIR PMT detector (Hamamatsu, H10330-45) equipped with a
1100 nm long-pass filter and additional selected narrow-band
filters. The sample absorbance was about 0.1 at the excitation
wavelength. The samples were excited at 440 nm with use of a
Xe lamp or a 40 MHz picosecond laser diode (LDH-440,
PicoQuant). A computer-mounted PCI-board multichannel
scaler (NanoHarp 250, PicoQuant) was used for data
collection.
Results and discussion
Nanosecond transient absorption spectra
Synthesis and characterization
The nanosecond transient absorption was measured with a Coordination of L1–L3 to the {Re(CO)3}+ core was achieved by a
system described previously.83 The experiments were carried well-established procedure, that is refluxing of [Re(CO)5Cl]
out in rectangular 1 cm × 1 cm quartz cells at room tempera- with one equivalent of the corresponding ligand in aceto-
ture. Diluted CH3CL or CH3CN solutions of 1 and 1A (Aλ
nitrile. The identity and purity of the ligands and Re(I) com-
=
355 nm: 0.2) were excited at 355 nm and the third harmonic of a plexes [ReCl(CO)3(Ln-κ2N)] were confirmed by FT-IR technique
Nd:YAG laser pulses (Spectra Physics, Mountain View, CA, (Fig. S1†), 1H and 13C NMR spectroscopy (Fig. S2–S7†) and
USA, model INDI 40-10) was employed as a pump. The 150 W elemental analysis. For 1 and L1, the full assignment of the
pulsed Xe lamp with a lamp pulser (Applied Photophysics, signals in the H and 13C NMR spectra was achieved by multi-
1
Surrey, UK), a monochromator (Princeton Instruments, Spectra dimensional techniques 1H–13C HMBC, 1H–13C HMQC, and
Pro SP-2357, Acton, MA, USA), and an R955 photomultiplier 1H–1H COSY (Fig. S2 and S5†). Due to the bidentate coordi-
(Hamamatsu, Japan), powered by a PS-310 power supply nation mode of L1–L3, the protons of the peripheral pyridyl/
(Stanford Research System, Sunnyvale, CA, USA) were used in a thiazolyl/pyrazinyl rings become magnetically inequivalent,
monitoring system. The data processing system consisted of and separated signals, each integrated for 1 proton, are
real-time acquisition using a digital oscilloscope (WaveRunner observed in the 1H NMR spectra of 1–3 (Fig. S2–S4†). The facial
6100A, LeCroy, Chestnut Ridge, NY, USA), which was triggered arrangement of CO groups in the moiety [Re(CO)3]+ is sup-
by a fast photodiode (Thorlabs, DET10 M, ca. 1 ns rise time) ported by the ν(CuO) bands, typical for this geometry set,
and transferred to a computer equipped with software based comprising the sharp intense absorption at higher wavenum-
on LabView 8.0 (National Instruments, Austin, TX, USA) which bers (2023–2021 cm−1) and two overlapping lower-energy ones
controlled the timing and acquisition functions of the system.
(1927–1889 cm−1) (Fig. S1†). The average CO stretching fre-
quencies (1942 cm−1 for 1, 1945 cm−1 for 2 and 1952 cm−1 for
3) indicates a decrease of the overall donor ability (including
Femtosecond transient absorption
The fs TA spectra were measured using a pump–probe transi- both σ-donor and π-acceptor contributions) of the chelating
ent absorption spectroscopy system (Ultrafast Systems, Helios) ligand in the order L1 > L2 > L3.11
described previously.84,85 The samples of 1, 1A, 1B, L1, L1A and
All Re(I) complexes were obtained as crystalline solids with
L1B were prepared in CHCl3, with absorbance in the range of melting temperature (Tm), identified by DSC measurements, in
0.2–0.7 in the excitation wavelengths (corresponding to con- the range of 210–261 °C (cf. Experimental section). Two of
centrations in the range of 5 × 10−5–2.5 × 10−4 mol dm−3 for them, that is with terpy (1) and dtpy (2) cores after rapid
ligands and 2.5 × 10−5–2.5 × 10−4 mol dm−3 for the com- cooling, can be converted into the amorphous state with the
plexes), and placed in 2 mm path length quartz cells with mag- glass transition temperature (Tg) registered in the second
netic stirring. The samples were pumped with 355 nm and heating scan at 205 and 208 °C, respectively. The Re(I) complex
420 nm pulses for 1, 1A and 1B, 355 nm for L1 and L1B and with the dppy structure (3) melted with decomposition. The
320 nm for L1A. Obtained data were analyzed using the Surface representative DSC thermograms are given in Fig. S8.†
3946 | Dalton Trans., 2021, 50, 3943–3958
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systems [ReCl(CO)3(Ln-κ2N)] without any groups attached to
the phenyl ring (1A–3A) and bearing pyrrolidine instead of car-
bazole (1B–3B).66
As a result of introducing the electron-donating 9-carbazole
unit, the HOMO energy level rises from −6.44 eV for 1A, −6.46
eV for 2A and −6.57 eV for 3A to −6.08 eV for 1, −6.09 eV for 2
and −6.09 eV for 3, respectively (Fig. 2 and Fig. S12 in ESI†).
The raised HOMO energy level may indicate better hole-trans-
porting properties of 1–3 compared to the parent complexes
1A–3A.95–97 In relation to the corresponding 1B–3B, however,
the HOMO orbital of the designed complexes (1–3) is more
effectively stabilized. The increase of HOMO energy in the fol-
lowing orders 1A < 1 < 1B, 2A < 2 < 2B and 3A < 3 < 3B is
accompanied by the increase of the energy difference between
the HOMO and HOMO−1. In contrast to 1A–3A, for which the
HOMO and HOMO−1 are very close in energy (energy gaps
0.12, 0.13, and 0.12 eV), the HOMO and HOMO−1 orbitals of
Fig. 1 Molecular structure of 2 with thermal ellipsoids set at 50% prob-
ability for non-hydrogen atoms. Selected bond lengths (Å) and angles (°)
associated with the Re(I) ion: Re(1)–N(1) 2.153(3), Re(1)–N(2) 2.243(3),
Re(1)–C(1) 1.916(4), Re(1)–C(2) 1.906(4), Re(1)–C(3) 1.916(4), Re(1)–Cl(1) 1–3 and 1B–3B become more energetically separated, with an
2.4836(10), N(1)–Re(1)–N(2) 74.37(11), N(1)–Re(1)–C(1) 173.48(13), N(1)–
Re(1)–C(2) 96.85(14), N(1)–Re(1)–C(3) 92.26(14), N(2)–Re(1)–C(1)
99.76(13), N(2)–Re(1)–C(2) 169.67(13), C(3)–Re(1)–N(2) 98.38(13), C(1)–
Re(1)–C(2) 88.70(16), C(1)–Re(1)–C(3) 91.43(16), C(2)–Re(1)–C(3)
energy gap of 0.37, 0.38 and 0.42 eV for 1–3 and 0.70, 0.67 and
0.78 eV for 1B–3B, respectively.
The LUMO level of 1–3 remains almost unchanged relative
to that for the corresponding one of 1A–3A, but it is slightly
lowered relative to that of appropriate 1B–3B. These findings
seem to be consistent with better π-delocalization properties of
the carbazole relative to pyrrolidine. For all three series, the
calculated HOMO–LUMO energy gap decreases in the order 1A
(3.82 eV) > 1 (3.43 eV) > 1B (3.23 eV), 2A (3.69 eV) > 2 (3.29 eV)
> 2B (3.12 eV) and 3A (3.62 eV) > 3 (3.12 eV) > 3B (2.91 eV).
Upon replacing the pyridyl by thiazolyl or pyrazinyl, the
HOMO energy level remains almost unchanged, while the
LUMO energy is stabilized in the order [ReCl(CO)3(R-terpy-
87.24(16), C(3)–Re(1)–Cl(1) 177.72(12), C(1)–Re(1)–Cl(1) 90.83(12), C(2)–
Re(1)–Cl(1) 92.47(12), N(1)–Re(1)–Cl(1) 85.53(8), N(2)–Re(1)–Cl(1) 81.57(8).
The X-ray crystal structure was obtained for 2, and the per-
spective view of its molecular structure together with selected
bond lengths (Å) and angles (°) associated with the Re(I) ion is
shown in Fig. 1.
The rhenium ion of 2 adopts a highly distorted octahedral
coordination geometry defined by three facially arranged car-
bonyl ligands, two nitrogen atoms of the L2 ligand and chlor-
ide ion. A significant distortion from the octahedral geometry,
largely reflected in a small bite angle N(2)–Re(1)–N(1) angle of
74.37(11)°, significant enlargement of the C(1)–Re(1)–N(2)
angle of 99.76(13)° and elongation of the Re(1)–N(2) bond
length to the central pyridine ring [2.243(3) Å] in relation to
the Re(1)–N(1) distance to the peripheral thiazole ring
[2.153(3) Å], is attributed to the κ2N-coordination of L2 and the
strong steric interaction of the uncoordinated thiazolyl ring
with the carbonyl group C(1)–O(1). The non-coordinated trii-
mine peripheral ring is inclined to the central pyridine at
49.91(14)°, while the dihedral angles between the phenyl ring
and central pyridine/carbazole planes are 34.67(19)° and
48.61(14)°, respectively. As can be expected, the carbazole unit
is more inclined towards phenyl and central pyridine rings
than pyrrolidine in 2B (Table S2†). Additional structural data
of 2 are available in the ESI (Tables S1–S3 and Fig. S9–S11†).
κ2N)]
< <
[ReCl(CO)3(R-dtpy-κ2N)] [ReCl(CO)3(R-dppy-κ2N)],
which leads to the decrease of the HOMO–LUMO energy gap
in this sequence (Fig. 3 and Fig. S12, S13†).
For all the Re(I) complexes, the LUMO and LUMO+1 reside
on the triimine moiety with partial contribution of π* orbitals
Frontier molecular orbital analysis
To gain better insight into how the N-carbazolyl unit intro-
duced into the terpy-like ligands influences HOMOs and
LUMOs and the HOMO–LUMO gap of [ReCl(CO)3(Ln-κ2N)], the
frontier molecular orbitals of 1–3 have been calculated at the
DFT/PBE1PBE/def2-TZVPD/def2-TZVP level, and their energies
Fig. 2 Partial molecular orbital energy levels of 1 in comparison with
the MO diagrams of the complexes 1A (without any group attached to
the phenyl ring) and 1B (bearing pyrrolidine instead of carbazole) (for 2
and characters were compared to those of previously reported and 3 see Fig. S12 in the ESI†).
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1B–3B in Table S5,† while Fig. S16† shows the CVs and DPVs
for 1–3.
The first reduction process of 1–3 occurs at similar poten-
tials as for 1A–3A and 1B–3B. Upon replacing pyridyl by thiazo-
lyl or pyrazinyl, the first quasi-reversible wave moves towards
more positive values. Additional N- or S-donor atom intro-
duced into the π-deficient trisheterocyclic unit of dtpy and
dppy results in increasing π-acceptor properties of the dtpy and
dppy ligand and leads to the stabilization of the LUMO level in
Re(I) carbonyls bearing 2,6-di(thiazol-2-yl)pyridine and 2,6-di
(pyrazin-2-yl)pyridine derivatives relative to those with
2,2′:6′,2′′-terpyridines, which is manifested by the appearance
of the first reduction peak at less negative potentials in the
order [ReCl(CO)3(R-terpy-κ2N)]
< <
[ReCl(CO)3(R-dtpy-κ2N)]
[ReCl(CO)3(R-dppy-κ2N)]. Such findings are consistent with the
theoretical calculations showing stabilization of the LUMO
level in this sequence. It is highly probable that the reduction
in 1–3 occurs in the triimine core. Nevertheless, the reduction
potentials of 1–3 are slightly affected by the electron-donating
substituent attached to the phenyl ring. Introduction of pyrro-
lidine gives rise to the most negative potential for the first
reduction wave in all three series 1A–1–1B, 2A–2–2B, and 3A–
3–3B.
The first oxidation peaks of 1–3 occur at potentials compar-
able to those for the parent complexes (1A–3A), which can
imply that they are associated with the oxidation of metal
centre Re(I/II).63,64,66,99 In contrast, the oxidation waves
Fig. 3 Partial MO diagrams for complexes 1–3.
of the phenyl group (Fig. S14 and S15†). A remarkable differ-
ence can be noticed in the HOMO character for [ReCl(CO)3(Ln-
κ2N)] without any groups attached to the phenyl ring (1A–3A)
and HOMO character for [ReCl(CO)3(Ln-κ2N)] bearing carbazole
(1–3) or pyrrolidine (1B–3B). For the latter ones (1–3 and 1B–
3B), the HOMO is largely defined by the electron-donating sub-
stituent (carbazole in 1–3 and pyrrolidine in 1B–3B) and the
phenylene linkage, while the HOMO of the parent complexes
(1A–3A) is located on the {Re(CO)3Cl} unit. Notably, the com-
plexes 1–3 and 1B–3B differ in percentage contribution of the
phenylene linkage, which is two times higher for Re(I) com-
plexes with the pyrrolidine group than for those bearing the
N-carbazolyl substituent (Fig. S15†). Additional theoretical
results, including ionization potentials (IPs), electronic affinities
95–97
(EAs) and reorganization energies (λhole and λelectron
)
for
1–3, 1A–3A and 1B–3B are given in the ESI (Tables S4†).
Electrochemistry
HOMO and LUMO energy levels and the band gap energy (Eg)
of 1–3 were also estimated experimentally with cyclic voltam-
metry (CV) and differential pulse voltammetry (DPV). The
studies were performed on a glassy carbon electrode in CH3CN
with 0.1 M n-Bu4NPF6 as the supporting electrolyte. The poten-
tials were referenced to the ferrocene/ferrocenium redox
couple, and onsets of the first oxidation and reduction waves
were used to estimate the values of IP and EA, which can be
regarded as closely related to the HOMO and LUMO levels,
respectively.98 The relevant electrochemical data of 1–3 are
summarized in Table 2, compared to those for 1A–3A and
Fig. 4 UV-Vis spectra of 1–3 in CHCl3 and CH3CN.
Table 2 Relevant electrochemical data of 1–3
Complex
Ered [V]
Ered(onset) [V]
Eox [V]
Eox(onset) [V]
EA [eV]
IP [eV]
Eg [eV]
1
2
3
−1.78a
−1.69a
−1.46a
−1.65
−1.59
−1.32
0.71b
0.78b
0.69b
0.59
0.66
0.55
−3.45
−3.51
−3.78
−5.69
−5.76
−5.65
2.24
2.25
1.87
IP = −5,1-Eox(onset), EA = −5,1-Ered(onset), Eg = Eox(onset) − Ered(onset). Solution: CH3CN, concentration: 10−3mol L−1, electrolyte: 0.1 M Bu4NPF6. GC as
the working electrode. a Quasi-reversible. b Irreversible.
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Table 3 The absorption maxima and molar extinction coefficient values for the complexes [ReCl(CO)3(Ln-κ2N)] (1–3)
Complex
Medium
λ/nm (104 ε/dm3 mol−1 cm−1
)
1
CH3CN
CHCl3
CH3CN
CHCl3
CH3CN
CHCl3
380 (1.52), 338 (1.63), 309 (2.34), 288 (3.63), 237 (6.67)
391 (1.51), 332 (1.67), 310 (2.73), 287 (3.87), 245 (6.46)
394 (1.58), 331 (2.44), 287 (3.73), 237 (6.35)
415 (1.47), 337 (2.57), 289 (3.91), 262 (4.03), 246 (5.48)
400 (0.47), 336 (0.91), 323 (1.06), 287 (1.43), 237 (2.53)
429 (0.45), 336 (0.99), 324 (1.10), 287 (1.41), 242 (2.93)
2
3
observed at much lower potentials of 1B–3B were assigned to
oxidation in the pyrrolidine moiety.66
Absorption spectral behavior and time-dependent DFT
calculations
The electronic absorption spectra of 1–3, registered in two sol-
vents of a different polarity are presented in Fig. 4, and the
relevant spectroscopic data for 1–3 and free ligands are sum-
marized in Table 3 (see also ESI, Fig. S17–S19 and Table S6†).
By comparing with the spectra of the free ligands, the high
energy absorptions of 1–3 are assigned to the π → π* tran-
sitions localized on the terpy-like ligand coordinated to the
metal center in a bidentate mode (Fig. S17†). The longest-wave-
length absorptions of 1–3, with maxima in the range
380–429 nm and much lower molar extinction coefficients,
possess charge transfer character. With the increase of the
solvent polarity from chloroform (ε = 4.8) to acetonitrile (ε =
37.5), the band is blue-shifted by 740 cm−1 for 1, 1284 cm−1
for 2 and 1690 cm−1 for 3 (see Table 3). Referring to the pre-
vious studies, the negative solvatochromic effect seems to be
typical of MLCT excited states in these systems.3,100,101
Expectedly, the replacement of the terpy core by dtpy and
dppy leads to the shift of the lowest energy band towards the
red end of the spectrum. This effect, observed also in the solid
(Fig. S19†), is attributed to the increase of ligand π-acceptor
properties owing to the introduction of additional donor
atoms into peripheral rings (S in dtpy and N in dppy). On the
Fig. 6 Experimental (red line) absorption spectra of 1–3 in CH3CN
alongside with transitions (black lines) computed at the TD-DFT/PCM/
PBE1PBE/def2-TZVPD/def2-TZVP level with the use of the PCM model
at polarities corresponding to CH3CN.
Fig. 5 UV-Vis spectroscopy properties of 1 in comparison to the spec-
tral profiles of 1A and 1B in CHCl3 and CH3CN.
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other hand, comparative analysis of absorption spectral pro- Luminescence
files of 1–3 with those for 1A–3A and 1B–3B, illustrated in
The photoluminescence (PL) and electroluminescence (EL)
capacity of the synthesized molecules was tested. PL pro-
perties of designed Re(I) complexes (1–3) were investigated in
non-polar and polar solvents (CHCl3, ε = 4.8 and MeCN, ε =
37.5), in low temperature glasses, in the form of a thin film
on glass substrates, and as blend with poly(N-vinylcarbazole)
(PVK) (50 wt%): 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-
oxadiazole (PBD) (50 wt%) with various Re(I) complex
content in a matrix (1, 2 and 15 wt%) (Tables 4, S8, S9 and
Fig. S21–S23 in the ESI†). Following photoexcitation at the
energetically lowest absorption band, the solutions of 1–3
exhibited emission with maxima falling in the range of
651–738 nm (Fig. 7a). Typically for a vast majority of
rhenium(I) carbonyls with terpy-like ligands, the complexes
1–3 have nanosecond lifetimes and low emission quantum
yield in solution at room temperature (from 0.51% to
1.39%).63–69,102 Due to some overlap of the ligand-localized
absorptions with those of the MLCT transitions, excitation of
1 in CHCl3 does not selectively excite MLCT. The residual
ligand fluorescence emission, observed as a shoulder at
506 nm, may indicate incomplete energy transfer occurring
from the 1ILCT/1IL to 1MLCT excited state.103,104 A similar
trend was also reported for 1B.66
Fig. 5 and Fig. S18,† shows that the appended N-carbazolyl
unit does not alter the energy of the longest-wavelength
absorption relative to the appropriate one of 1A–3A, but results
in a significant increase in its molar absorption coefficient. In
relation to the Re(I) complexes with ligands bearing pyrrolidine
instead of the 9-carbazole group (1B–3B), the long-wave
absorption of 1–3 is more symmetrical, less intense, and
appears at a higher energy, which may indicate minor contri-
bution of intraligand charge-transfer (ILCT) transitions from
the donor orbital localized on the 9-carbazole to the triimine-
based π* acceptor orbital than from pyrrolidine to the triimine
acceptor.
To gain insight into the nature of the excited states of 1–3,
the computational studies at the TD-DFT/PCM/PBE1PBE/def2-
TZVPD/def2-TZVP level were undertaken (Fig. 6). According to
the theoretical calculations, the low-energy absorption band of
1–3 is composed of several transitions of different origins
(Fig. S20 and Table S7†), but predominant contribution can be
assigned to the excitations HOMO → LUMO, HOMO →
LUMO+1 and HOMO−1 → LUMO for complexes 1–2, and
HOMO → LUMO, HOMO → LUMO+1 and HOMO−2 → LUMO
for 3. Based on the MO composition, the transitions HOMO−1
→ LUMO for 1 and 2 and HOMO−2 → LUMO for 3 can be allo-
cated as 1MLCT [dπ(Re) → π*(triimine)], while HOMO → LUMO
and HOMO → LUMO+1 are best described as charge transfer
The frozen-state (77 K) emission of 1–3 appears in the
higher energy region (540–581 nm) due to the rigidochromic
effect,43,105 and is characterised by lifetimes in microseconds
with electronic density originating from the 9-carbazole donor (Table 4 and Table S8†). Except for 1 at 77 K, the emission of
unit to the π-conjugated triimine acceptor moiety (1ILCT). designed complexes is structureless, which may indicate the
Therefore, the low-energy absorption band of 1–3 can be charge transfer character of the excited state. A weak vibronic
assigned to a combination of 1ILCT and 1MLCT transitions.
structure observed in the emission spectrum of 1 at low temp-
erature may arise due to some degree of mixing between CT
and 3IL/ILCT excited states (Fig. 7b).3,106
Taking into consideration the triimine skeleton, it can be
noticed that the emission of the Re(I) complex with the
2,2′:6′,2′′-terpyridine-based ligand (1) appears at a significantly
higher energy in relation to that for 2 and 3, both in solution
and in a matrix at low temperature. The solid state emission of
the designed complexes systematically moves towards the red
3
In accordance with the experimental data, the calculated
low energy excitations for 1–3 fall in the same energy range as
for 1A–3A, but they are blue-shifted relative to those for 1B–3B
of predominant ILCT character. Higher oscillator strength
values for the calculated low energy excitations of 1–3 in
relation to those for 1A–3A correlate with a significant increase
in molar absorption coefficients of the low-energy absorption
bands of 1–3.
Table 4 Summary of photoluminescence properties of 1–3
Complex
Medium
Excitation
Emission
Lifetime [ns]
χ2
φ [%]
1
MeCN
CHCl3
370, 326, 282, 254
385, 316, 287, 261
651
506
657
513, 540
596
0.58 (13.33%), 2.60 (86.67%)
7.74 (76.77%), 2.90 (23.23%)
3.17 (73.15%), 7.66 (26.85%)
9874 (41.66%), 38 355 (58.34%)
332.71
0.955
1.044
1.052
1.080
0.958
0.58
1.39
77 K (EtOH : MeOH 4 : 1 v/v)
Solid
400, 322, 289, 278, 240
486
—
15.42
2
3
MeCN
CHCl3
386, 334, 304, 253
410, 334, 265
402, 327, 287, 239
494
733
734
578
618
3.98
5.78
0.961
1.086
1.131
1.076
0.92
0.77
—
77 K (EtOH : MeOH 4 : 1 v/v)
Solid
2635 (56.68%), 9826 (43.32%)
46.67 (38.05%); 300.57 (61.95%)
7.55
MeCN
CHCl3
400, 322, 288
411, 326, 287, 259
421, 331, 288
512
734
738
578
638
3.35
0.996
1.016
1.126
1.000
0.51
0.99
—
3.95 (53.05%), 9.26 (46.95%)
29 376 (52.62%), 156 554 (47.38%)
30.44 (21.47%); 114.69 (78.53%)
77 K (EtOH : MeOH 4 : 1 v/v)
Solid
8.60
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Compared to the recently reported tricarbonyl rhenium(I)
complexes of 2-pyridyl-1,2,n-triazole (pyta) bidentate
ligands,108,109 the lifetimes of 1–3 are shorter, but their values,
markedly increased in relation to those in solutions, are
indicative that the nature of solid-state emission is largely of
phosphorescence origin. To examine whether the observed
increase of the quantum yields of 1–3 in the solid state relative
to those in solutions can be assigned to aggregation induced
emission phenomenon, the emission spectra of 1–3 in mix-
tures of acetonitrile and water were recorded. As shown in
Fig. 8, for mixtures with water fraction ( fw) above 70%, the
emission wavelength of 1–3 moves towards higher energy and
luminescence intensity significantly increases, which can be
assigned to the phosphorescence emission upon aggregation
(AIPE) effect.109 In the case of mixtures with water fraction
below 50%, the emission maxima of 1 and 3 show bathochro-
mic shifts accompanied by a noticeable luminescence inten-
sity decrease. These findings can be explained by the fact that
water as a polar solvent stabilizes the ILCT excited state and
simultaneously decreases the luminescence intensity, which is
in agreement with the decrease of quantum yield of 1 and 3
upon going from chloroform to acetonitrile solution (Table 4).
To better understand the impact of the N-carbazolyl group
on the emission properties of [ReCl(CO)3(Ln-κ2N)], the photo-
physical data of 1–3 were analysed by comparison to those for
parent complexes (1A–3A) and those bearing pyrrolidine
instead of carbazole (1B–3B).
Noteworthy, different trends can be noticed for appropriate
compounds belonging to the series 1A–3A, 1–3 and 1B–3B
depending on the environment. For matrices at low temperature,
the emission of 1–3 covers the range similar to that of 1A–3A,
while the appropriate complex from the series 1B–3B emits in a
lower-energy region (Fig. S21 and Table S8 in the ESI†). The
same relation is seen for 1A–1–1B and 3A–3–3B in acetonitrile
Fig. 7 Normalized emission spectra of 1–3 in solution at room temp-
erature (a), in a low temperature matrix (77 K in EtOH–MeOH (4 : 1 v/v))
(b), solid state as powder (c), and in film (d).
end in the order 1 (596 nm) < 2 (618 nm) < 3 (638 nm)
(Fig. 7c), except for complex 1 in film (Fig. 7d). The bathochro-
mic shift is accompanied by the shortening of the lifetimes
(332.7 ns for 1 > 204.0 ns for 2 > 96.6 ns for 3), in accord with
the energy gap law.3,107
Fig. 8 Emission spectra of 1 in the CH3CN/water mixture with different
water fractions ( fw). (for complexes 2 and 3 see Fig. S24 in the ESI†).
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solution, contrary to the compounds 2A–2–2B, for which there is Nano- and femtosecond transient absorption
no marked difference in emission energy (Fig. S21 in ESI†). In
To further investigate the nature of the excited states in the
chloroform, the complexes 1B–3B show hypsochromically shifted
emission maxima in relation to those of appropriate complexes
of the series 1A–3A and 1–3, while the emissions of the latter
ones cover almost the same range (Fig. S21†). Inspecting the
photoluminescence lifetimes of 1–3 at 77 K and in the solid state
by comparison with 1A–3A and 1B–3B, it can be noticed that the
introduction of the pyrrolidine into terpy/dtpy/dppy skeleton
leads to a remarkable increase in lifetimes (Table S8†). Given all
these considerations, it can be assumed that the excited states of
1–3 are very likely of the MLCT character, similar to the parent
complexes 1A–3A. For 1B–3B, the deactivation process seems to
be also involved by ILCT excited states, and the involvement of
ILCT transitions is increasing with the solvent polarity. Very
strongly donating groups lead to a significant lifetime extension
of [ReCl(CO)3(Ln-κ2N)], which strongly justifies exploring substi-
tuent-related modifications in these systems.
Considering that the Re(I) complexes exhibited photo-
luminescence in the solid state with a significantly higher PL
quantum yield compared to the solution, the effect of its
chemical structure on capacity for light emission under
applied voltage was also preliminarily examined and compared
with the previously reported systems 1A and 1B 66 (Fig. 9 and
Table S10†). The advantage impact of the presence of the terpy
core and pyrrolidine unit on the emission of light induced by
external voltage was observed.
examined compounds, transient absorption studies in nano-
(nTA) and femto-second (fsTA) regimes were performed for the
series 1A–1–1B (Fig. 10 and 13 as well as Fig. S25–S28 in the
ESI†).
With reference to the parent complex [ReCl(CO)3(bipy)],35,36,104
we can safely assume that the formation of the triplet states of
1A, 1 and 1B occurs at the ultrafast time delay. Formation of
the triplet excited-states in 1A, 1 and 1B was additionally evi-
denced by singlet oxygen photoluminescence in the near-IR at
1270 nm (Fig. 11).
Noteworthy, the fsTA spectra of 1 and 1A resemble each
other and they display very similar TA features to the complex
[ReCl(CO)3(bipy)].35,36,104 The ESA band at ∼370 nm for 1A and
∼355 nm for 1 is characteristic of transitions localized on the
bpy•− core. In the case of 1, this band is slightly blue shifted
due to the introduction of the electron-donating 9-carbazole.
The broad bands in the visible region of TA spectra of 1 and
1A correspond to Cl/L−•− → Re (Ligand-to-Metal-Charge-
Transfer, LMCT) transitions coupled with reorganization of
electron density within the {ReCl(CO)3} moiety. A slight red-
shift of the visible ESA band of 1 relative to 1A corresponds to
increasing structural π-conjugation due to the attachment of
the 9- carbazole group. An additional component in the decay
associated spectrum of 1 (Fig. 10b, 15.7 ps) relative to 1A is
3
supportive for the involvement of the ILCT/3IL configuration
Fig. 9 EL spectra of the selected diodes containing Re(I) complexes: ITO/PEDOT:PSS/complex/Al and ITO/PEDOT:PSS/PVK:PBD:complex/Al for 1 (a);
ITO/PEDOT:PSS/PVK:PBD:complex/Al for 1, 2 and 3 with complex content in blend of 1% (b), 2% (c) and 15% (d). All spectra are scaled to the left Y
axis, except for the blue spectrum on graph (a) ITO/PEDOT:PSS/1/Al (15 V), which is referenced on the right Y axis.
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Fig. 10 Femtosecond transient absorption spectra at selected delay times (a) together with decay associated spectra (DAS) (b) for 1 and 1A.
in the emitting state of 1. The lifetimes deduced from the
decay of the TA signals of the both complexes (3.1 ns for 1 and
3.9 ns for 1A) appear to be the same within experimental error,
and they are essentially the same as those obtained from the
decay of emission (3.2 ns for 1 and 3.3 ns for 1A), indicating
that emitting excited states can be observed in the TA states of
3MLCT character (Tables S11 and S12†). Nanosecond transient
absorption spectra of 1 are shown in Fig. 12. The line shape of
the relaxed excited-states spectral feature in the fsTA regime
quantitatively matches the nanosecond TA difference spectra,
indicating that there are no additional excited states observed
between the femtosecond and nanosecond time domains.
Observed nanosecond transient absorptions, due to their short
lifetimes (basically comparable to the laser pulse duration of
ca. 10 ns) could be attributed to the S1 → Sn transitions.
However, taking into consideration strong resemblance to
[ReCl(CO)3(bipy)], for which intersystem crossing occurs at the
ultrafast time delay,35,36,104 as well as the fact that short
Fig. 11 Singlet oxygen generation of complexes 1, 1A and 1B. Data for
complex 1B taken from ref. 66.
3MLCT lifetimes (from 0.58 to 2.3 ns) were recently evidenced
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Fig. 12 Nanosecond transient absorption spectra of CH3CN and 1 in CH3CN and CHCl3 (a); the nsTA decay kinetics at 400 nm for 1 (b) (for com-
plexes 1A and 1B see Fig. S25 in the ESI†).
in related rhenium(I) κ2N-tricarbonyl complexes with 4′-(4-sub- accordance with 1MLCT/1ILCT of 1B, significant red-shift of
stituted-phenyl)-terpyridine ligands using transient IR spec- the broad bands in the visible region of TA spectra and sub-
troscopy (TRIR),102 they seem to be rather of 3MLCT origin. On stantial increase in the TA triplet lifetime relative to 1 and
the other hand, the compounds 1 and 1A were found to gene- model complex 1A (Fig. 13). Determined using nTA spec-
rate singlet oxygen with a moderately high yield (Fig. 11), and troscopy lifetimes of 1B in argon-saturated and air-saturated
this generation requires a contribution of longer-lived triplet acetonitrile solutions are 774 and 162 ns, respectively.66 The
excited state. As confirmed by kinetic fit (Fig. 12b), the dark most reasonable explanation of these observations is signifi-
3
3
3
triplet T1 → Tn absorption of the IL/3ILCT character with life- cant mixing of MLCT and ILCT/3IL excited states, supported
time ∼28 µs is overlapped with the ground state absorption.
also by PL studies.110–112 The 3MLCT energy in the complex 1B
The attachment of pyrrolidine resulted in the appearance of was estimated to be 18 421 cm−1, while the triplet energy of
the clear bleaching at the wavelength (∼425 nm) that was in the free ligand was ca. 21 000 cm−1. In the case of 1, the
Fig. 13 Femtosecond transient absorption spectra at select delay times (a) together with decay associated spectra (DAS) (b) for 1B and L1B
.
3954 | Dalton Trans., 2021, 50, 3943–3958
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3ILCT/3IL state is energetically higher and its population from
Acknowledgements
3
3
3MLCT is inefficient. The energies of MLCT and ILCT/3IL in
1 were estimated to be 18 611 cm−1 and 23 732 cm−1, respect- The research was co-financed by the National Science Centre
ively (Fig. S29 and S30†). of Poland grant no. 2017/25/B/ST5/01611 (BM) and 2017/27/B/
Additional data concerning transient absorption studies in ST3/02457 (SM). The calculations were carried out in Wroclaw
nano- and femto-second regimes for 1A, 1 and 1B are available Centre for Networking and Supercomputing (http://www.wcss.
in the ESI (Fig. S25–S28 and Tables S11–S14†).
wroc.pl). The authors would like to kindly thank Dr T.
Klemens for providing samples of complexes 1A and 1B and
Dr S. Kotowicz for luminescence measurements.
Conclusions
Three novel complexes [ReCl(CO)3(Ln-κ2N)] bearing 2,2′:6′,2′′-
terpyridine, 2,6-di(thiazol-2-yl)pyridine and 2,6-di(pyrazin-
2-yl)pyridine functionalized with 9-carbazole attached to the
central pyridine ring of the triimine core via phenylene
linkage were synthetized. All the complexes were characterized
electrochemically and photophysically. Their ground- and
excited-state properties were compared with those of pre-
viously reported analogous systems – without any group
attached to the phenyl ring and bearing pyrrolidine instead of
9-carbazole. It was evidenced that the introduction of the elec-
tron-donating 9-carbazole unit did not alter noticeably the
energy of the longest-wavelength absorption relative to the
References
1 M. Wrighton and D. L. Morse, J. Am. Chem. Soc., 1974, 96,
998–1003.
2 A. Coleman, C. Brennan, J. G. Vos and M. T. Pryce, Coord.
Chem. Rev., 2008, 252, 2585–2595.
3 A. Kumar, S.-S. Sun and A. J. Lees, in Photophysics of
Organometallics, ed. A. J. Lees, Springer Berlin Heidelberg,
Berlin, Heidelberg, 2010, pp. 37–71.
4 H. Takeda, K. Koike, T. Morimoto, H. Inumaru and
O. Ishitani, in Advances in Inorganic Chemistry, ed. R. van
Eldik and G. Stochel, Academic Press, 2011, vol. 63, pp.
137–186.
1
corresponding parent complex. Due to the ILCT involvement,
only substantial increase of molar absorption coefficients was
confirmed. The attachment of 9-carbazole to the triimine
ligand did not lead to a switch in the nature of the lowest-
lying triplet excited state. TA spectra of the [ReCl(CO)3(L1-κ2N)]
showed high similarity to those of the parent complex
[ReCl(CO)3(4′-Ph-terpy-κ2N)] and related [ReCl(CO)3(bipy)]. It
was observed that the presence of the dppy unit in complex (3)
raises the melting temperature to from ca. 210 °C (1 and 2) to
260 °C, but together with melting the thermal decomposition
is seen. Additionally, the compounds with terpy (1) and dtpy
(2) core can be converted into stable amorphous material with
high Tg (ca. 200 °C), which can give opportunity for the
preparation of uniform amorphous thin films. It should be
noticed that the all investigated complexes exhibited photo-
luminescence in the solid state. The replacements of dppy (3)
and dtpy (2) with terpy (1) resulted in the highest PL quantum
yield in the solid state and emission of light under external
voltage by a diode with a neat 1 applied as the active layer.
Moreover, the guest–host device based on the complex with
the terpy (1) unit showed the most intense EL. It was found
that substitution of the phenyl ring in the triimine core and
the replacement the carbazole substituent with the pyrrolidine
structure raises the light emission intensity induced by
voltage. To rationally design new functional materials with
pre-defined photophysical behaviour, further substituent-
related modifications in these systems deserve more
exploration.
5 C.-C. Ko, A. W.-Y. Cheung, L. T.-L. Lo, J. W.-K. Siu,
C.-O. Ng and S.-M. Yiu, Coord. Chem. Rev., 2012, 256,
1546–1555.
6 W.-K. Chung, K. M.-C. Wong, W. H. Lam, X. Zhu, N. Zhu,
H.-S. Kwok and V. W.-W. Yam, New J. Chem., 2013, 37,
1753–1767.
7 L. Sanhueza, M. Barrera and I. Crivelli, Polyhedron, 2013,
57, 94–104.
8 A. Woźna and A. Kapturkiewicz, Phys. Chem. Chem. Phys.,
2015, 17, 30468–30480.
9 C. Chen, Y. Xu, Y. Wan, W. Fan and Z. Si, Eur. J. Inorg.
Chem., 2016, 2016, 1340–1347.
10 S. Mai, H. Gattuso, M. Fumanal, A. Muñoz-Losa,
A. Monari, C. Daniel and L. González, Phys. Chem. Chem.
Phys., 2017, 19, 27240–27250.
11 L. Suntrup, S. Klenk, J. Klein, S. Sobottka and B. Sarkar,
Inorg. Chem., 2017, 56, 5771–5783.
12 M. Pinto, I. Chakraborty, J. Martinez-Gonzalez and
P. Mascharak, Acta Crystallogr., Sect. C: Struct. Chem.,
2017, 73, 923–929.
13 R. C. Amaral and N. Y. M. Iha, Dalton Trans., 2018, 47,
13081–13087.
14 R. Kia, S. Mahmoudi and P. R. Raithby, CrystEngComm,
2018, 21, 77–93.
15 A. N. Hellman, R. Haiges and S. C. Marinescu, Dalton
Trans., 2019, 48, 14251–14255.
16 N. Pizarro, M. Duque, E. Chamorro, S. Nonell, J. Manzur,
J. R. de la Fuente, G. Günther, M. Cepeda-Plaza and
A. Vega, J. Phys. Chem. A, 2015, 119, 3929–3935.
17 L.-X. Zhao, J. Sherchan, J. K. Park, Y. Jahng, B.-S. Jeong,
T. C. Jeong, C.-S. Lee and E.-S. Lee, Arch. Pharmacal Res.,
2006, 29, 1091–1095.
Conflicts of interest
There are no conflicts to declare.
This journal is © The Royal Society of Chemistry 2021
Dalton Trans., 2021, 50, 3943–3958 | 3955

View Article Online
Paper
Dalton Transactions
18 R.-R. Ye, C.-P. Tan, M.-H. Chen, L. Hao, L.-N. Ji and
Z.-W. Mao, Chem. – Eur. J., 2016, 22, 7800–7809.
19 L. C.-C. Lee, K.-K. Leung and K. K.-W. Lo, Dalton Trans.,
2017, 46, 16357–16380.
20 Y.-X. Hu, G.-W. Zhao, Y. Dong, Y.-L. Lü, X. Li and
D.-Y. Zhang, Dyes Pigm., 2017, 137, 569–575.
21 S. Hostachy, C. Policar and N. Delsuc, Coord. Chem. Rev.,
2017, 351, 172–188.
41 H.-Y. Li, J. Wu, X.-H. Zhou, L.-C. Kang, D.-P. Li, Y. Sui,
Y.-H. Zhou, Y.-X. Zheng, J.-L. Zuo and X.-Z. You, Dalton
Trans., 2009, 10563–10569.
42 A. Vlček, in Photophysics of Organometallics, ed. A. J. Lees,
Springer, Berlin, Heidelberg, 2010, pp. 115–158.
43 D. Wang, Q.-L. Xu, S. Zhang, H.-Y. Li, C.-C. Wang, T.-Y. Li,
Y.-M. Jing, W. Huang, Y.-X. Zheng and G. Accorsi, Dalton
Trans., 2013, 42, 2716–2723.
22 J. K. Nganga, C. R. Samanamu, J. M. Tanski, C. Pacheco,
C. Saucedo, V. S. Batista, K. A. Grice, M. Z. Ertem and
A. M. Angeles-Boza, Inorg. Chem., 2017, 56, 3214–
3226.
23 P. V. Simpson, M. Falasca and M. Massi, Chem. Commun.,
2018, 54, 12429–12438.
24 C. B. Larsen and O. S. Wenger, Inorg. Chem., 2018, 57,
2965–2968.
25 X. Ji, P. Zhang, W. Wei, H. Zhang and B. Xia, J. Organomet.
Chem., 2018, 862, 40–52.
44 H. van der Salm, C. B. Larsen, J. R. W. McLay,
M. G. Fraser, N. T. Lucas and K. C. Gordon, Dalton Trans.,
2014, 43, 17775–17785.
45 W.-K. Chu, X.-G. Wei, S.-M. Yiu, C.-C. Ko and K.-C. Lau,
Chem. – Eur. J., 2015, 21, 2603–2612.
46 C. Liu, J. Li, B. Li, Z. Hong, F. Zhao, S. Liu and W. Li, Appl.
Phys. Lett., 2006, 89, 243511.
47 C. Jia, S.-X. Liu, C. Tanner, C. Leiggener, A. Neels,
L. Sanguinet, E. Levillain, S. Leutwyler, A. Hauser and
S. Decurtins, Chem. – Eur. J., 2007, 13, 3804–3812.
48 X. Liu, H. Xia, W. Gao, Q. Wu, X. Fan, Y. Mu and C. Ma,
J. Mater. Chem., 2012, 22, 3485–3492.
26 Y. Kuramochi, O. Ishitani and H. Ishida, Coord. Chem.
Rev., 2018, 373, 333–356.
27 Z. Hao, N. Li, X. Yan, X. Yue, K. Liu, H. Liu, Z. Han and
J. Lin, J. Organomet. Chem., 2018, 870, 51–57.
28 A. El Nahhas, A. Cannizzo, F. van Mourik, A. M. Blanco-
Rodríguez, S. Záliš, A. Vlček and M. Chergui, J. Phys.
Chem. A, 2010, 114, 6361–6369.
29 A. Rondi, Y. Rodriguez, T. Feurer and A. Cannizzo, Acc.
Chem. Res., 2015, 48, 1432–1440.
30 S. Záliš, C. Consani, A. E. Nahhas, A. Cannizzo,
M. Chergui, F. Hartl and A. Vlček, Inorg. Chim. Acta, 2011,
374, 578–585.
31 D. M. Dattelbaum, K. M. Omberg, P. J. Hay, N. L. Gebhart,
R. L. Martin, J. R. Schoonover and T. J. Meyer, J. Phys.
Chem. A, 2004, 108, 3527–3536.
32 D. M. Dattelbaum, K. M. Omberg, J. R. Schoonover,
R. L. Martin and T. J. Meyer, Inorg. Chem., 2002, 41, 6071–
6079.
33 D. J. Liard, M. Busby, P. Matousek, M. Towrie and
A. Vlček, J. Phys. Chem. A, 2004, 108, 2363–2369.
34 F. Würthner, Acc. Chem. Res., 2016, 49, 868–876.
35 A. Cannizzo, A. M. Blanco-Rodríguez, A. El Nahhas,
J. Šebera, S. Záliš, A. Vlček and M. Chergui, J. Am. Chem.
Soc., 2008, 130, 8967–8974.
36 A. El Nahhas, C. Consani, A. M. Blanco-Rodríguez,
K. M. Lancaster, O. Braem, A. Cannizzo, M. Towrie,
I. P. Clark, S. Záliš, M. Chergui and A. Vlček, Inorg. Chem.,
2011, 50, 2932–2943.
49 L. Ordronneau, H. Nitadori, I. Ledoux, A. Singh,
J. A. G. Williams, M. Akita, V. Guerchais and H. Le Bozec,
Inorg. Chem., 2012, 51, 5627–5636.
50 T. Yu, D. P.-K. Tsang, V. K.-M. Au, W. H. Lam, M.-Y. Chan
and V. W.-W. Yam, Chem. – Eur. J., 2013, 19, 13418–13427.
51 Y. Yue, T. Grusenmeyer, Z. Ma, P. Zhang, T. T. Pham,
J. T. Mague, J. P. Donahue, R. H. Schmehl, D. N. Beratan
and I. V. Rubtsov, J. Phys. Chem. B, 2013, 117, 15903–
15916.
52 A. Breivogel, C. Kreitner and K. Heinze, Eur. J. Inorg.
Chem., 2014, 2014, 5468–5490.
53 C. B. Larsen, H. van der Salm, C. A. Clark, A. B. S. Elliott,
M. G. Fraser, R. Horvath, N. T. Lucas, X.-Z. Sun,
M. W. George and K. C. Gordon, Inorg. Chem., 2014, 53,
1339–1354.
54 H. van der Salm, M. G. Fraser, R. Horvath, J. O. Turner,
G. M. Greetham, I. P. Clark, M. Towrie, N. T. Lucas,
M. W. George and K. C. Gordon, Inorg. Chem., 2014, 53,
13049–13060.
55 G. S. Huff, W. K. C. Lo, R. Horvath, J. O. Turner, X.-Z. Sun,
G. R. Weal, H. J. Davidson, A. D. W. Kennedy,
C. J. McAdam, J. D. Crowley, M. W. George and
K. C. Gordon, Inorg. Chem., 2016, 55, 12238–12253.
56 C. B. Larsen, H. van der Salm, G. E. Shillito, N. T. Lucas
and K. C. Gordon, Inorg. Chem., 2016, 55, 8446–8458.
57 L. D. Ramos, R. N. Sampaio, F. F. de Assis, K. T. de
Oliveira, P. Homem-de-Mello, A. O. T. Patrocinio and
K. P. M. Frin, Dalton Trans., 2016, 45, 11688–11698.
58 B. S. Adams, G. E. Shillito, H. van der Salm, R. Horvath,
C. B. Larsen, X.-Z. Sun, N. T. Lucas, M. W. George and
K. C. Gordon, Inorg. Chem., 2017, 56, 12967–12977.
59 X. Li, G.-W. Zhao, Y.-X. Hu, J.-H. Zhao, Y. Dong, L. Zhou,
Y.-L. Lv, H.-J. Chi and Z. Su, J. Mater. Chem. C, 2017, 5,
7629–7636.
37 A. I. Baba, J. R. Shaw, J. A. Simon, R. P. Thummel and
R. H. Schmehl, Coord. Chem. Rev., 1998, 171, 43–59.
38 D. J. Stufkens and A. Vlček, Coord. Chem. Rev., 1998, 177,
127–179.
39 A. Vlček and M. Busby, Coord. Chem. Rev., 2006, 250,
1755–1762.
40 M. K. Kuimova, W. Z. Alsindi, A. J. Blake, E. S. Davies,
D. J. Lampus, P. Matousek, J. McMaster, A. W. Parker,
M. Towrie, X.-Z. Sun, C. Wilson and M. W. George, Inorg.
Chem., 2008, 47, 9857–9869.
60 G. E. Shillito, T. B. J. Hall, D. Preston, P. Traber, L. Wu,
K. E. A. Reynolds, R. Horvath, X. Z. Sun, N. T. Lucas,
3956 | Dalton Trans., 2021, 50, 3943–3958
This journal is © The Royal Society of Chemistry 2021

View Article Online
Dalton Transactions
Paper
J. D. Crowley, M. W. George, S. Kupfer and K. C. Gordon,
J. Am. Chem. Soc., 2018, 140, 4534–4542.
K. Erfurt and A. Chrobok, Org. Biomol. Chem., 2016, 14,
3793–3808.
61 K. S. Kisel, T. Eskelinen, W. Zafar, A. I. Solomatina,
P. Hirva, E. V. Grachova, S. P. Tunik and I. O. Koshevoy,
Inorg. Chem., 2018, 57, 6349–6361.
77 A. Maroń, S. Kula, A. Szlapa-Kula, A. Świtlicka,
B. Machura, S. Krompiec, J. G. Małecki, R. Kruszyński,
A. Chrobok, E. Schab-Balcerzak, S. Kotowicz, M. Siwy,
K. Smolarek, S. Maćkowski, H. Janeczek and M. Libera,
Eur. J. Org. Chem., 2017, 2017, 2730–2745.
78 J. Wang and G. S. Hanan, Synlett, 2005, 1251–1254.
79 L. Li, K. Du, Y. Wang, H. Jia, X. Hou, H. Chao and L. Ji,
Dalton Trans., 2013, 42, 11576–11588.
80 Z. Yin, G. Zhang, T. Phoenix, S. Zheng and J. C. Fettinger,
RSC Adv., 2015, 5, 36156–36166.
81 CrysAlis PRO, Oxford Diffraction Ltd, Yarnton, England,
2011.
82 G. M. Sheldrick, Acta Crystallogr., Sect. C: Struct. Chem.,
2015, 71, 3–8.
83 T. Pedzinski, A. Markiewicz and B. Marciniak, Res. Chem.
Intermed., 2009, 35, 497–506.
84 K. Choroba, S. Kula, A. Maroń, B. Machura,
J. Małecki, A. Szłapa-Kula, M. Siwy, J. Grzelak,
S. Maćkowski and E. Schab-Balcerzak, Dyes Pigm., 2019,
169, 89–104.
62 J. E. Barnsley, G. E. Shillito, C. B. Larsen, H. van der Salm,
R. Horvath, X. Z. Sun, X. Wu, M. W. George, N. T. Lucas
and K. C. Gordon, Inorg. Chem., 2019, 58, 9785–9795.
63 T. Klemens, A. Świtlicka-Olszewska, B. Machura,
M. Grucela, H. Janeczek, E. Schab-Balcerzak, A. Szlapa,
S. Kula, S. Krompiec, K. Smolarek, D. Kowalska,
S. Mackowski, K. Erfurt and P. Lodowski, RSC Adv., 2016,
6, 56335–56352.
64 T. Klemens, A. Świtlicka-Olszewska, B. Machura,
M. Grucela, E. Schab-Balcerzak, K. Smolarek,
S. Mackowski, A. Szlapa, S. Kula, S. Krompiec, P. Lodowski
and A. Chrobok, Dalton Trans., 2016, 45, 1746–1762.
65 T. Klemens, K. Czerwińska, A. Szlapa-Kula, S. Kula,
A. Świtlicka, S. Kotowicz, M. Siwy, K. Bednarczyk,
S. Krompiec, K. Smolarek, S. Maćkowski, W. Danikiewicz,
E. Schab-Balcerzak and B. Machura, Dalton Trans., 2017,
46, 9605–9620.
66 T. Klemens, A. Świtlicka, A. Szlapa-Kula, S. Krompiec,
P. Lodowski, A. Chrobok, M. Godlewska, S. Kotowicz,
M. Siwy, K. Bednarczyk, M. Libera, S. Maćkowski,
T. Pędziński, E. Schab-Balcerzak and B. Machura, Appl.
Organomet. Chem., 2018, 32, e4611.
67 T. Klemens, A. Świtlicka, S. Kula, M. Siwy, K. Łaba,
J. Grzelak, M. Szalkowski, S. Maćkowski, E. Schab-
Balcerzak and B. Machura, J. Lumin., 2019, 209, 346–356.
68 T. Klemens, A. Świtlicka, B. Machura, S. Kula,
S. Krompiec, K. Łaba, M. Korzec, M. Siwy, H. Janeczek,
E. Schab-Balcerzak, M. Szalkowski, J. Grzelak and
S. Maćkowski, Dyes Pigm., 2019, 163, 86–101.
85 A. M. Maroń, K. Choroba, T. Pedzinski and B. Machura,
Dalton Trans., 2020, 49, 13440–13448.
86 M. J. Frisch, G. W. Trucks, J. R. Cheeseman, G. Scalmani,
M. Caricato, H. P. Hratchian, X. Li, V. Barone, J. Bloino,
G. Zheng, T. Vreven, J. A. Montgomery, G. A. Petersson,
G. E. Scuseria, H. B. Schlegel, H. Nakatsuji, A. F. Izmaylov,
R. L. Martin, J. L. Sonnenberg, J. E. Peralta, J. J. Heyd,
E. Brothers, F. Ogliaro, M. Bearpark, M. A. Robb,
B. Mennucci, K. N. Kudin, V. N. Staroverov, R. Kobayashi,
J. Normand, A. Rendell, R. Gomperts, V. G. Zakrzewski,
M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao and H. Nakai,
Gaussian 09.
87 J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett.,
1996, 77, 3865–3868.
88 C. Adamo and V. Barone, J. Chem. Phys., 1999, 110, 6158–
6170.
89 F. Weigend and R. Ahlrichs, Phys. Chem. Chem. Phys.,
2005, 7, 3297–3305.
90 D. Rappoport and F. Furche, J. Chem. Phys., 2010, 133,
134105.
69 M. Małecka, B. Machura, A. Świtlicka, S. Kotowicz,
G. Szafraniec-Gorol, M. Siwy, M. Szalkowski, S. Maćkowski
and E. Schab-Balcerzak, Spectrochim. Acta, Part A, 2020,
231, 118124.
70 J. Strahan, B. C. Popere, P. Khomein, C. A. Pointer,
S. M. Martin, A. N. Oldacre, S. Thayumanavan and
E. R. Young, Dalton Trans., 2019, 48, 8488–8501.
71 Q. Zhang, J. Li, K. Shizu, S. Huang, S. Hirata, H. Miyazaki
and C. Adachi, J. Am. Chem. Soc., 2012, 134, 14706–14709.
72 M. Song, J. S. Park, Y.-S. Gal, S. Kang, J. Y. Lee, J. W. Lee
and S.-H. Jin, J. Phys. Chem. C, 2012, 116, 7526–7533.
73 M. Lepeltier, F. Appaix, Y. Y. Liao, F. Dumur, J. Marrot,
T. Le Bahers, C. Andraud and C. Monnereau, Inorg. Chem.,
2016, 55, 9586–9595.
91 D. Andrae, U. Häußermann, M. Dolg, H. Stoll and
H. Preuß, Theor. Chim. Acta, 1990, 77, 123–141.
92 E. Cancès, B. Mennucci and J. Tomasi, J. Chem. Phys.,
1997, 107, 3032–3041.
93 B. Mennucci and J. Tomasi, J. Chem. Phys., 1997, 106,
5151–5158.
74 P. Pander, R. Motyka, P. Zassowski, M. Lapkowski,
A. Swist and P. Data, J. Phys. Chem. C, 2017, 121, 11027–
11036.
94 M. Cossi, V. Barone, B. Mennucci and J. Tomasi, Chem.
Phys. Lett., 1998, 286, 253–260.
75 E. Matteucci, A. Baschieri, L. Sambri, F. Monti, E. Pavoni,
E. Bandini and N. Armaroli, ChemPlusChem, 2019, 84,
1353–1365.
76 A. Maroń, A. Szlapa, T. Klemens, S. Kula, B. Machura,
S. Krompiec, J. G. Małecki, A. Świtlicka-Olszewska,
95 R. Srivastava and L. R. Joshi, Phys. Chem. Chem. Phys.,
2014, 16, 17284–17294.
96 S.-J. Liu, N.-N. Song, J.-X. Wang, Y.-Q. Huang, Q. Zhao,
X.-M. Liu, S. Sun and W. Huang, Phys. Chem. Chem. Phys.,
2011, 13, 18497–18506.
This journal is © The Royal Society of Chemistry 2021
Dalton Trans., 2021, 50, 3943–3958 | 3957

View Article Online
Paper
Dalton Transactions
97 Y. Wang, Q. Peng, Y. Liang, B. Li and W. Zhu, 105 A. J. Lees, Chem. Rev., 1987, 87, 711–743.
Aust. J. Chem., 2011, 64, 1475–1484.
98 P. Bujak, I. Kulszewicz-Bajer, M. Zagorska, V. Maurel,
106 D. J. Casadonte and D. R. McMillin, J. Am. Chem. Soc.,
1987, 109, 331–337.
I. Wielgus and A. Pron, Chem. Soc. Rev., 2013, 42, 8895– 107 J. R. Lakowicz, Principles of Fluorescence Spectroscopy,
8999. Springer US, 3rd edn, 2006.
99 P. Gómez-Iglesias, F. Guyon, A. Khatyr, G. Ulrich, 108 J. Wang, B. Delavaux-Nicot, M. Wolff, S. Mallet-Ladeira,
M. Knorr, J. M. Martín-Alvarez, D. Miguel and F. Villafañe,
Dalton Trans., 2015, 44, 17516–17528.
R. Métivier, E. Benoist and S. Fery-Forgues, Dalton Trans.,
2018, 47, 8087–8099.
100 S.-T. Lam, N. Zhu and V. W.-W. Yam, Inorg. Chem., 2009, 109 J. Wang, A. Poirot, B. Delavaux-Nicot, M. Wolff, S. Mallet-
48, 9664–9670.
Ladeira, J. P. Calupitan, C. Allain, E. Benoist and S. Fery-
Forgues, Dalton Trans., 2019, 48, 15906–15916.
110 A. Del Guerzo, S. Leroy, F. Fages and R. H. Schmehl, Inorg.
Chem., 2002, 41, 359–366.
111 X. Wang, A. Del Guerzo and R. H. Schmehl, J. Photochem.
Photobiol., C, 2004, 5, 55–77.
112 N. D. McClenaghan, Y. Leydet, B. Maubert, M. T. Indelli
and S. Campagna, Coord. Chem. Rev., 2005, 249,
1336–1350.
101 G. Knör, M. Leirer and A. Vogler, J. Organomet. Chem.,
2000, 610, 16–19.
102 R. Fernández-Terán and L. Sévery, Inorg. Chem., 2021, 60,
1334–1343.
103 K. A. Wells, J. E. Yarnell, J. R. Palmer, T. S. Lee, C. M. Papa
and F. N. Castellano, Inorg. Chem., 2020, 59, 8259–8271.
104 L. Xiao, Y. Xu, M. Yan, D. Galipeau, X. Peng and X. Yan,
J. Phys. Chem. A, 2010, 114, 9090–9097.
3958 | Dalton Trans., 2021, 50, 3943–3958
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