Quantum mechanical and molecular dynamics simulations have been carried out on a series of anthracene‐o‐carborane derivatives (ANT‐H, ANT‐Ph, ANT‐Me and ANT‐TMS) with rare red‐light emission in the ...solid state. The simulation of the heating process of the crystals and further comparison of the molecular structures and excited‐state properties before and after heating help us to disclose the thermochromic behavior, that is, the red‐shift emission is caused by elongation of the C1−C2 bond in the carborane moiety after heating. Thus, we believe that the molecular structure in the crystal is severely affected by heating. Transformation of the molecular conformation appears in the ANT‐H crystal with increasing temperature. More specifically, the anthracene moiety moves from nearly parallel to the C1−C2 bond to nearly perpendicular, causing the short‐wavelength emission to disappear after heating. As for the aggregation‐induced emission phenomenon, the structures and photophysical properties were investigated comparatively in both the isolated and crystal states; the results suggested that the energy dissipation in crystal surroundings was greatly reduced through hindering structure relaxation from the excited to the ground state. We expect that discussion of the thermochromic behavior will provide a new analysis perspective for the molecular design of o‐carborane derivatives.
When the heat is on: A series of anthracene‐o‐carborane derivatives with red‐light aggregation‐induced emission has been studied theoretically. The changes in bond length and dihedral angle result from alteration of the crystal stacking structure after heating, and the thermochromic behavior in crystal is ascribed to the elongation of bond length.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The emergence and development of radical luminescent materials is a huge breakthrough toward high-performance organic light-emitting diodes (OLEDs) without spin-statistical limits. Herein, we design ...a series of radicals based on tris(2,4,6-trichlorophenyl)methyl (TTM) by combining skeleton-engineering and periphery-engineering strategies, and present some insights into how different chemical modifications can modulate the chemical stability and luminescence properties of radicals by quantum chemistry methods. Firstly, through the analysis of the geometric structure changes from the lowest doublet excited state (D
1
) to the doublet ground state (D
0
) states, the emission energy differences between the BN orientation isomers are explained, and it is revealed that the radical with a smaller dihedral angle difference can more effectively suppress the geometric relaxation of the excited states and bring a higher emission energy. Meanwhile, a comparison of the excited state properties in different radicals can help us to disclose the luminescence behavior, that is, the enhanced luminescent intensity of the radical is caused by the intensity borrowing between the charge transfer (CT) state and the dark locally excited (LE) state. In addition, an efficient algorithm for calculating the internal conversion rate (
k
IC
) is introduced and implemented, and the differences in
k
IC
values between designed radicals are explained. More specifically, the delocalization of hole and electron wave functions can reduce nonadiabatic coupling matrix elements (NACMEs), thus hindering the non-radiative decay process. Finally, the double-regulation of chemical stability and luminescence properties was realized through the synergistic effect of skeleton-engineering and periphery-engineering, and to screen the excellent doublet emitter (
BN-41-MPTTM
) theoretically.
A series of radicals based on tris(2,4,6-trichlorophenyl)methyl (TTM) were theoretically designed and evaluated by combining skeleton-engineering and periphery-engineering strategies.
The case that aggregation has a large influence on the structure and fluorescent properties of 5‐(4‐(1,2,2‐triphenylvinyl)phenyl)thiophene‐2‐carbaldehyde (P4TA) is investigated in detail herein by ...employing quantum mechanics and molecular mechanics. Besides the isolated molecule, the aggregated molecule in water and in the crystalline state was studied by focusing on the comparison of photoelectronic properties, including the geometrical and electronic structures at ground and excited states, emission and internal conversation properties. For the aggregation state, the intermolecular interaction was used to explain the difference in structure, emission color and intensity of different polymorphs. The noticeable contribution from low‐frequency region, corresponding to the four phenyl rings twisting vibration, to the Huang–Rhys factor and reorganization energy, as well as the possible potential energy surface crossing between S0 and S1 states for isolated molecules was considered as the reason of its aggregation‐induced emission (AIE) performance. Importantly, the aggregation process in water simulated at the same time helps us to have a deeper understanding of the AIE behavior of P4TA, which also provides another perspective to explore the AIE phenomenon in theory.
Limit rotation for brightness: The effects of aggregation on structural and spectral properties for a tetraphenylethylene derivative in both water and crystalline surroundings (see picture) are described. In the isolated molecule, the phenyl ring twisting motions cause large Huang–Rhys factors and possible potential energy surface crossings, which raise the nonradiative rate. While in aggregation, the rotational motions are restricted, leading to brighter emission.
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Available for:
FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
High-performance luminescent radical-based materials are emerging and are in demand for application in organic light-emitting diodes (OLEDs). Herein, quantum chemistry methods are employed to ...investigate a series of donoracceptor (DA) type monoradical molecules based on the tris(2,4,6-trichlorophenyl)methyl (TTM) acceptor and triarylamine (TPA) donor. The major factors affecting the device performance of the monoradical molecules, including thermodynamic stability, excited state characteristics and luminescence properties, are taken into consideration. The introduction of donor fragments can help to tune the luminescent properties of the monoradical molecule, and furthermore, the electron donating abilities of donor fragments, revealed by molecular Mulliken electronegativity, are negatively associated with both the stability and photoluminescence quantum yield (PLQY). The hybrid transition characteristic formed by the combination of charge transfer (CT) and localized excitation (LE) makes a significant contribution to the luminescence intensity of the monoradical molecules. Comparative analyses can lead us to conclude that monoradical molecules
1
,
2
,
3
,
4
,
6
and
8
possess more significant stability and photoluminescence efficiency, and are expected to become high-performance luminescent materials. Finally, our investigations show that in order to enhance the thermodynamic stability and PLQY, it should be appropriately considered to weaken the electron donating ability of donor fragments in the TTM-based D-A type of monoradical molecules by rational chemical modifications.
Spin-unrestricted DFT and spin-unrestricted TDDFT calculations were performed to systematically investigate the correlation between the electron donating ability of donors and photophysical properties in D-A luminescent radicals.
The interface characteristic is a crucial factor determining the power conversion efficiency of organic solar cells (OSCs). In this work, our aim is to conduct a comparative study on the interface ...characteristics between the very famous non-fullerene acceptor, ITIC, and a fullerene acceptor, PC71BM by combining molecular dynamics simulations with density functional theory. Based on some typical interface models of the acceptor ITIC or PC71BM and the donor PBDB-T selected from MD simulation, besides the evaluation of charge separation/recombination rates, the relative positions of Frenkel exciton (FE) states and the charge transfer states along with their oscillator strengths are also employed to estimate the charge separation abilities. The results show that, when compared with those for the PBDB-T/PC71BM interface, the CT states are more easily formed for the PBDB-T/ITIC interface by either the electron transfer from the FE state or direct excitation, indicating the better charge separation ability of the former. Moreover, the estimation of the charge separation efficiency manifests that although these two types of interfaces have similar charge recombination rates, the PBDB-T/ITIC interface possesses the larger charge separation rates than those of the PBDB-T/PC71BM interface. Therefore, the better match between PBDB-T and ITIC together with a larger charge separation efficiency at the interface are considered to be the reasons for the prominent performance of ITIC in OSCs.
In this work, a series of homoleptic monocyclic and 2catenanes gold(
i
) thiolates were studied by DFT and TD-DFT methods to analyze the relationship between structure and property. The results ...reveal that the increase of Au-S-Au bond angles in
Au11
and
Au12
makes the 2catenanes more planar than the monocyclic molecules. The smaller Au Au contacts tighten the overall structure and enhance its geometrical stability. There is a positive correlation between the Au percentage in the frontier molecular orbitals and the orbital energy levels for both monocyclic molecules and 2catenanes. The HOMO levels of the 2catenanes are higher than those of the monocyclic molecules, which may be caused by stronger Au Au Pauli repulsion. Differences in size and metallophilic interactions are responsible for the different absorption spectra of the complexes, and the electronic spectral redshift of the 2catenanes is consistent with their higher HOMO energy levels. The results of energy decomposition analysis indicate that electrostatic interaction and orbital interaction are the main driving forces of molecular formation. In 2catenanes, Pauli repulsion and steric interaction can be balanced. The calculated results of interaction energy and stabilization energy suggest that 2catenanes are very stable. The calculated reaction enthalpies indicate that the chemical stabilization of 2catenanes decreased in the order of
Au12
,
Au11
, and
Au10
.
To compare homoleptic 2catenanes and single rings consisting of gold(
i
) thiolates, the geometric and electronic structures, absorption spectra, binding energy, interaction energy and composition of intramolecular forces were studied theoretically.
In a variety of skeletal structures of delayed fluorescence molecular materials, the donor-acceptordonor (D-A-D) type has been widely considered for improving the efficiency of the reverse ...intersystem crossing (RISC) process. Herein, three new D-A-D molecules (PTZ-MPS, TPA-MPS and PCz-MPS) bearing 9,9-dimethylthioxanthene-S,S-sulfur dioxide (MPS) as the electron acceptor group are designed and investigated using theoretical calculations. PTZ-MPS shows the feature of the high-lying reverse intersystem crossing process, which is conducive to improving the exciton utilization of organic light-emitting diodes (OLEDs). PTZ-MPS has a much smaller singlettriplet energy splitting (
E
S
1
T
3
= 0.03 eV) than TPA-MPS (Δ
E
S
1
T
3
= 0.32 eV) and PCz-MPS (
E
S
1
T
3
= 0.59 eV). However, it has a much larger spinorbital coupling (SOC) strength (S
1
SOC
|T
3
〉 = 1.013 cm
−1
) than TPA-MPS (〈S
1
|
SOC
|T
3
= 0.311 cm
−1
) and PCz-MPS (〈S
1
|
SOC
|T
3
〉 = 0.354 cm
−1
), which makes it easy to induce a sufficient RISC from the T
n
state to the S
1
state. The Δ
E
ST
and SOC are the two most important factors in determining TADF molecules. Therefore, PTZ-MPS is expected to be a potential high-lying excited state delayed fluorescence material candidate, and our work demonstrates that high-performance TADF materials can also be obtained successfully by designing rational molecules.
DFT and TD-DFT calculations were performed to turn conventional non-TADF units into high-lying reverse intersystem crossing D-A-D-type TADF emitters.
Two o -carborane derivatives 1 and 2 exhibiting both aggregation induced emission (AIE) and thermally activated delayed fluorescence (TADF) properties were investigated by combining density ...functional theory with molecular dynamics simulation. The reason for their TADF property was explored. Besides, taking 1 as an example, the AIE phenomenon was also probed by simulating the aggregation process and comparing the photophysical properties of the molecules in different aggregation states (including crystals, water, and films) with the isolated molecule. The results manifest that the separated orbital occupations of the HOMO and LUMO at the respective donor and acceptor units result in a small singlet–triplet energy gap and a favorable TADF feature, which is similar to many typical TADF molecules. In the AIE phenomenon, a much smaller structural change of donor and acceptor units between S 1 and S 0 states was experienced for the molecules in all aggregate states compared with that for the isolated molecule, decreasing the energy dissipation substantially and enhancing the luminescence efficiency. In addition, o -carborane is conjectured to help in the free rotation of donor and acceptor units for the isolated molecule, which may contribute to AIE. What's more, on the basis of 1 and 2 , we designed 3–6 by means of replacing the triphenyltriazine group with other electron-withdrawing groups having lower LUMO energy levels, aiming to obtain this kind of red light emitting material. The results indeed proved our assumption that 3–6 not only present the feature of red light emission but also have both TADF and AIE properties in films.
White organic light-emitting diodes (WOLEDs) achieving high electroluminescence (EL) performance and tiny efficiency roll-off concurrently have been highly desired for practical application. ...Orange-red luminescence is well-known as an important component of WOLEDs, however, the development of such materials with high efficiency is still challenging due to the relatively poor emission caused by the energy-gap law and the concentration quenching phenomenon. Herein, two orange-red emitting iridium(
iii
) complexes
Ir(pq)
2
pbi
and
Ir(piq)
2
pbi
with isomeric cyclometalated ligands,
i.e.
2-phenylquinoline and 1-phenylisoquinoline, are designed and synthesized. The structural modulation adjusts not only the conjugation degree but also the molecular packing of both complexes, resulting in distinctly different photophysical and EL performance. The utility of
Ir(pq)
2
pbi
in a monochromic device shows a current efficiency (
η
c
) of 36.7 cd A
−1
, a power efficiency (
η
p
) of 22.6 lm W
−1
, and an external quantum efficiency (
η
ext
) as high as 16.0% along with negligible efficiency roll-off, which are much better than those of
Ir(piq)
2
pbi
. Two-color complementary WOLEDs based on
Ir(pq)
2
pbi
as a dopant realize an
η
c
of 39.8 cd A
−1
, an
η
p
of 31.3 lm W
−1
, and an
η
ext
of 17.3% with a low
η
ext
roll-off ratio of 2.3%, respectively. Such excellent electroluminescence performance for monochromic and WOLEDs suggests the potential of
Ir(pq)
2
pbi
for further display application and will guide further molecular design in the future.
Molecular isomeric engineering is employed to construct efficient orange-red Ir(
iii
) complexes for WOLEDs and understand the intrinsic structure-property relationship.
Constructing deep-red Ir(
iii
) phosphors featuring sufficient luminous efficiency is highly desirable but remains challenging owing to their severe nonradiative decay. Herein, two structurally ...simple Ir(
iii
) complexes, namely
Ir(iqbt)
2
IPO
and
Ir(qabt)
2
IPO
, with cyclometalated ligands modulated by nitrogen atoms were developed. Both complexes showed efficient deep-red phosphorescence with the desired emission peaked at approximately 680 nm and shoulder peaks at 735 nm. Complex
Ir(qabt)
2
IPO
with a high nitrogen atom doping ratio exhibited a much higher emission intensity accompanied by a better PLQY of 21.4% relative to that of
Ir(iqbt)
2
IPO
(16.3%). Analysis of the excited electronic structures of both complexes indicated that such high emission efficiency could stem from the augmentation of the MLCT character. Consequently,
Ir(qabt)
2
IPO
based OLED displayed more than twofold improvement in the maximum external quantum efficiency, exceeding that of
Ir(iqbt)
2
IPO
and affording the deep-red electroluminescence with CIE coordinates at (0.72, 0.27). Therefore, designing cyclometalated ligands by introducing extra nitrogen atoms provides an effective strategy for exploring deep-red Ir(
iii
) complexes and OLEDs.
By introducing more nitrogen atoms into molecular skeleton, deep-red-emitting
Ir(qabt)
2
IPO
exhibits higher PLQY and EQE compared with referent
Ir(iqbt)
2
IPO
.
