scholarly journals Electronic structure and photophysics of a supermolecular iron complex having a long MLCT-state lifetime and panchromatic absorption

2020 ◽  
Vol 117 (34) ◽  
pp. 20430-20437
Author(s):  
Ting Jiang ◽  
Yusong Bai ◽  
Peng Zhang ◽  
Qiwei Han ◽  
David B. Mitzi ◽  
...  
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Density Functional ◽  
Energy Levels ◽  
High Energy ◽  
Iron Complex ◽  
Oxidation Potential ◽  
Tridentate Ligand ◽  
Electronically Excited ◽  
Mlct State

Exploiting earth-abundant iron-based metal complexes as high-performance photosensitizers demands long-lived electronically excited metal-to-ligand charge-transfer (MLCT) states, but these species suffer typically from femtosecond timescale charge-transfer (CT)-state quenching by low-lying nonreactive metal-centered (MC) states. Here, we engineer supermolecular Fe(II) chromophores based on the bis(tridentate-ligand)metal(II)-ethyne-(porphinato)zinc(II) conjugated framework, previously shown to give rise to highly delocalized low-lying3MLCT states for other Group VIII metal (Ru, Os) complexes. Electronic spectral, potentiometric, and ultrafast pump–probe transient dynamical data demonstrate that a combination of a strong σ-donating tridentate ligand and a (porphinato)zinc(II) moiety with low-lying π*-energy levels, sufficiently destabilize MC states and stabilize supermolecular MLCT states to realize Fe(II) complexes that express3MLCT state photophysics reminiscent of their heavy-metal analogs. The resulting Fe(II) chromophore archetype, FeNHCPZn, features a highly polarized CT state having a profoundly extended3MLCT lifetime (160 ps),3MLCT phosphorescence, and ambient environment stability. Density functional and domain-based local pair natural orbital coupled cluster [DLPNO-CCSD(T)] theory reveal triplet-state wavefunction spatial distributions consistent with electronic spectroscopic and excited-state dynamical data, further underscoring the dramatic Fe metal-to-extended ligand CT character of electronically excited FeNHCPZn. This design further prompts intense panchromatic absorptivity via redistributing high-energy absorptive oscillator strength throughout the visible spectral domain, while maintaining a substantial excited-state oxidation potential for wide-ranging photochemistry––highlighted by the ability of FeNHCPZn to photoinject charges into a SnO2/FTO electrode in a dye-sensitized solar cell (DSSC) architecture. Concepts enumerated herein afford opportunities for replacing traditional rare-metal–based emitters for solar-energy conversion and photoluminescence applications.

scholarly journals Effect of hybridized local and charge transfer molecules rotation in excited state on exciton utilization

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Gang Sun ◽  
Xin-Hui Wang ◽  
Jing Li ◽  
Bo-Ting Yang ◽  
Ying Gao ◽  
...  
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Energy Level ◽  
High Performance ◽  
Density Functional ◽  
Energy Gap ◽  
Energy Levels ◽  
Density Functional Theory Method ◽  
Molecular Structures ◽  
State Potential

AbstractThe fluorescent molecules utilizing hybridized local and charge-transfer (HLCT) state as potential organic light-emitting diodes materials attract extensive attention due to their high exciton utilization. In this work, we have performed the density functional theory method on three HLCT-state molecules to investigate their excited-state potential energy surface (PES). The calculated results indicate the T1 and T2 energy gap is quite large, and the T2 is very close to S1 in the energy level. The large gap is beneficial for inhibiting the internal conversion between T1 and T2, and quite closed S1 and T2 energies are favor for activating the T2 → S1 reverse intersystem crossing path. However, considering the singlet excited-state PES by twisting the triphenylamine (TPA) or diphenylamine (PA) group, it can be found that the TPA or PA group almost has no influence on T1 and T2 energy levels. However, the plots of S1 PES display two kinds of results that the S1 emissive state is dominated by charge-transfer (CT) or HLCT state. The CT emission state formation would decrease the S1 energy level, enlarge the S1 and T2 gap, and impair the triplet exciton utilization. Therefore, understanding the relationship between the S1 PES and molecular structures is important for designing high-performance luminescent materials utilizing HLCT state.

In silico study of binding affinity of nitrogenous bicyclic heterocycles: fragment-to-fragment approach

2020 ◽  
Vol 15 (2) ◽  
pp. 49-59
Author(s):  
Yevheniia Velihina ◽  
Nataliya Obernikhina ◽  
Stepan Pilyo ◽  
Maryna Kachaeva ◽  
Oleksiy Kachkovsky ◽  
...  
Keyword(s):  
Amino Acids ◽  
Binding Affinity ◽  
In Silico ◽  
Density Functional ◽  
Energy Levels ◽  
Aromatic Amino Acids ◽  
Electron System ◽  
High Energy ◽  
Proton Donor ◽  
Stabilization Energy

The binding affinity of model aromatic amino acids and heterocycles and their derivatives condensed with pyridine were investigated in silico and are presented in the framework of fragment-to-fragment approach. The presented model describes interaction between pharmacophores and biomolecules. Scrupulous data analysis shows that expansion of the π-electron system by heterocycles annelation causes the shifting up of high energy levels, while the appearance of new the dicoordinated nitrogen atom is accompanied by decreasing of the donor-acceptor properties. Density Functional Theory (DFT) wB97XD/6-31(d,p)/calculations of π-complexes of the heterocycles 1-3 with model fragments of aromatic amino acids, which were formed by π-stack interaction, show an increase in the stabilization energy of π-complexes during the moving from phenylalanine to tryptophan. DFT calculation of pharmacophore complexes with model proton-donor amino acid by the hydrogen bonding mechanism (H-B complex) shows that stabilization energy (DE) increases from monoheterocycles to their condensed derivatives. The expansion of the π-electron system by introducing phenyl radicals to the oxazole cycle as reported earlier [18] leads to a decrease in the stabilization energy of the [Pharm-BioM] complexes in comparison with the annelated oxazole by the pyridine cycle.

scholarly journals Ultrafast charge transfer dynamics in 2D Covalent Organic Frameworks/Re-complex hybrid photocatalyst for CO2 reduction: hot electrons vs. cold electrons

2021 ◽  
Author(s):  
Qinying Pan ◽  
Mohamed Abdellah ◽  
Yuehan Cao ◽  
Yang Liu ◽  
Weihua Lin ◽  
...  
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Excitation Energy ◽  
Co2 Reduction ◽  
Underlying Mechanism ◽  
High Energy ◽  
Hot Electrons ◽  
Covalent Organic Frameworks ◽  
Energy Excitation ◽  
Energy Dependent

Abstract Rhenium(I)-carbonyl-diimine complexes are promising photocatalysts for CO2 reduction. Covalent organic frameworks (COFs) can be perfect sensitizers to enhance the reduction activities. Here we investigated the excited state dynamics of COF (TpBpy) with 2,2'-bipyridine incorporating Re(CO)5Cl (Re-TpBpy) to rationalize the underlying mechanism. The time-dependent DFT calculation first clarified excited state structure of the hybrid catalyst. The studies from transient visible and infrared spectroscopies revealed the excitation energy-dependent photo-induced charge transfer pathways in Re-TpBpy. Under low energy excitation, the electrons at the LUMO level are quickly injected from Bpy into ReI center (1–2 ps) followed by backward recombination (13 ps). Under high energy excitation, the hot-electrons are first injected into the higher unoccupied level of ReI center (1–2 ps) and then slowly relax back to the HOMO in COF (24 ps). There also remains long-lived free electrons in the COF moiety. This explained the excitation energy-dependent CO2 reduction performance in our system.

A density functional theory and spectroscopic study of intramolecular quenching of metal-to-ligand charge-transfer excited states in some mono-bipyridine ruthenium(II) complexes

2014 ◽  
Vol 92 (10) ◽  
pp. 996-1009 ◽  
Author(s):  
Shivnath Mazumder ◽  
Ryan A. Thomas ◽  
Richard L. Lord ◽  
H. Bernhard Schlegel ◽  
John F. Endicott
Keyword(s):  
Density Functional Theory ◽  
Excited State ◽  
Charge Transfer ◽  
Excited States ◽  
Lower Energy ◽  
Density Functional ◽  
Dimethyl Sulfide ◽  
Intramolecular Electron Transfer ◽  
Functional Theory ◽  
Ligand Charge Transfer

The complexes [Ru(NCCH3)4bpy]2+ and [Ru([14]aneS4)bpy]2+ ([14]aneS4 = 1,4,8,11-tetrathiacyclotetradecane, bpy = 2,2′-bipyridine) have similar absorption and emission spectra but the 77 K metal-to-ligand charge-transfer (MLCT) excited state emission lifetime of the latter is less than 0.3% that of the former. Density functional theory modeling of the lowest energy triplet excited states indicates that triplet metal centered (3MC) excited states are about 3500 cm−1 lower in energy than their 3MLCT excited states in both complexes. The differences in excited state lifetimes arise from a much larger coordination sphere distortion for [Ru(NCCH3)4bpy]2+ and the associated larger reorganizational barrier for intramolecular electron transfer. The smaller ruthenium ligand distortions of the [Ru([14]aneS4)bpy]2+ complex are apparently a consequence of stereochemical constraints imposed by the macrocyclic [14]aneS4 ligand, and the 3MC excited state calculated for the unconstrained [Ru(S(CH3)2)4bpy]2+ complex (S(CH3)2 = dimethyl sulfide) is distorted in a manner similar to that of [Ru(NCCH3)4bpy]2+. Despite the lower energy calculated for its 3MC than 3MLCT excited state, [Ru(NCCH3)4bpy]2+ emits strongly in 77 K glasses with an emission quantum yield of 0.47. The emission is biphasic with about a 1 μs lifetime for its dominant (86%) emission component. The 405 nm excitation used in these studies results in a significant amount of photodecomposition in the 77 K glasses. This is a temperature-dependent biphotonic process that most likely involves the bipyridine-radical anionic moiety of the 3MLCT excited state. A smaller than expected value found for the radiative rate constant is consistent with a lower energy 3MC than 3MLCT state.

scholarly journals Multireference Description of Nickel–Aryl Homolytic Bond Dissociation Processes in Photoredox Catalysis

2020 ◽  
Author(s):  
David Cagan ◽  
Gautam Stroscio ◽  
Alexander Cusumano ◽  
Ryan Hadt
Keyword(s):  
Electronic Structure ◽  
Excited State ◽  
Charge Transfer ◽  
Density Functional ◽  
Single Photon ◽  
Ligand Field ◽  
Initial Population ◽  
Bond Dissociation ◽  
Ligand Charge Transfer ◽  
Triplet Excited States

<p>Multireference electronic structure calculations consistent with known experimental data have elucidated a novel mechanism for photo-triggered Ni(II)–C homolytic bond dissociation in Ni 2,2’-bipyridine (bpy) photoredox catalysts. Previously, a thermally assisted dissociation from the lowest energy triplet ligand field excited state was proposed and supported by density functional theory (DFT) calculations that reveal a barrier of ~30 kcal mol<sup>-1</sup>. In contrast, multireference ab initio calculations suggest this process is disfavored, with barrier heights of ~70 kcal mol<sup>-1</sup>, and highlight important ligand noninnocent contributions to excited state relaxation and bond dissociation processes that are not captured with DFT. In the multireference description, photo-triggered Ni(II)–C homolytic bond dissociation occurs via initial population of a singlet Ni(II)-to-bpy metal-to-ligand charge transfer (<sup>1</sup>MLCT) excited state followed by intersystem crossing and aryl-to-Ni(III) charge transfer, overall a formal two-electron transfer process driven by a single photon. This results in repulsive triplet excited states from which spontaneous homolytic bond dissociation can occur, effectively competing with relaxation to the lowest energy, nondissociative triplet Ni(II) ligand field excited state. These findings guide important electronic structure considerations for the experimental and computational elucidation of the mechanisms of ground and excited state cross-coupling catalysis mediated by Ni heteroaromatic complexes.</p>

Accurate description of hybridized local and charge-transfer excited-state in donor–acceptor molecules using density functional theory

RSC Advances ◽  
2016 ◽  
Vol 6 (110) ◽  
pp. 108404-108410 ◽  
Author(s):  
Y. Y. Pan ◽  
J. Huang ◽  
Z. M. Wang ◽  
S. T. Zhang ◽  
D. W. Yu ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Excited State ◽  
Charge Transfer ◽  
Ground State ◽  
Density Functional ◽  
Accurate Description ◽  
Functional Theory ◽  
Donor Acceptor ◽  
Acceptor Molecules

The ωB97X was the most reliable functional for the accurate description of HLCT state at ground state and excited state.

scholarly journals Pyrimidine, an Intermediate State Molecule?

1986 ◽  
Vol 5 (6) ◽  
pp. 339-350 ◽  
Author(s):  
W. Leo Meerts ◽  
W. A. Majewski
Keyword(s):  
Excited State ◽  
High Resolution ◽  
Ring Laser ◽  
Fluorescence Spectra ◽  
Molecular Beam ◽  
Energy Levels ◽  
Laser Induced Fluorescence ◽  
Spectral Features ◽  
Electronically Excited State ◽  
Electronically Excited

The S1(1B1) ← S0(1A1) transition in pyrazine has been investigated. High resolution laser induced fluorescence spectra were obtained by crossing a well collimated molecular beam with UV radiation of an intra-cavity frequency doubled ring laser. The extreme resolution enabled us to observe the molecular eigenstates of the electronically excited state. Most of the spectral features of the S1 state could be interpreted in terms of a slightly perturbed axis switched rotor spectrum. The perturbations show up both in the energy levels of the S1 and in the intensities of the observed transitions.

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