Predicting absorption spectra of silver‐ligand complexes

Abstract

The detailed structures of most of ligand-stabilized metal nanoclusters (NCs) remain unknown due to the absence of crystal structure data for them. In such a situation, quantum-chemical modeling is of particular interest. We compared the performance of different theoretical methods of geometry optimization and absorption spectra calculation for silver-thiolate complexes. We showed that the absorption spectra calculated with the ADC(2) method were consistent with the spectra obtained with CC2 method. Three DFT functionals (B3LYP, CAM-B3LYP, and M06-2X) failed to reproduce the CC2 absorption spectra of the silver-thiolate complexes. K E Y W O R D SADC(2), CAM-B3LYP, CC2, M062X, silver nanoclusters, silver-thiolate complexes, TDDFT | INTRODUCTIONLigand protected metal nanoclusters (NCs) have gained much attention in the last decade due to their unique physicochemical properties. These metal NCs typically measure less than 2 nm. [1,2] Electronic, chemical, and optical properties of NCs differ from both bulk and atomic scale materials. Optically active NCs may possess strong visible or near infrared luminescence, [3] which can be used in various applications, such as bioimaging, biosensing, and optical detection of biomolecules. [4] Among the great variety of NCs, gold (Au) NCs are the most extensively investigated due to their chemical stability. [5] However, fluorescent silver (Ag) clusters are the brightest, exhibiting high quantum yield and large absorption cross-section. [6] Various techniques have been developed for the synthesis of stable, water-soluble silver NCs by using dendrimers, [7] polymers, [8] polypeptides, [9,10] thiols, [11] DNA, [12,13] thiolated DNA, [14] and other ligands to stabilize silver ions. [15] The influence of various thiolates on binding energy with silver NCs has been studied in details. [16] The nature of the ligand seems to have a strong effect on fluorescent properties of noble metal NCs. [17] Noble metal NCs protected with thiolate ligands have been of interest because of their long-term stability, which allows one to use them as building blocks constructing assembled systems with novel and improved functions. [2] Silver-thiolate and silver-amino acid complexes are studied in many laboratories nowadays both theoretically and experimentally. [18][19][20] It is assumed that silver nanoclusters are stabilized by cysteine residues in protein matrices. [21,22] While the composition of the ligand-protected NCs can be analyzed using mass-spectroscopy technique, [23] their detailed structures remain unknown in many cases. In this respect, quantum-chemical modeling of silver-ligand complexes is of particular interest. [24][25][26][27][28][29][30][31][32] Gell and coworkers investigated thiolate-protected silver NCs that contained zero, two, or four confined electrons in the cluster core. [33] They found that the number of confined electrons determine the spectroscopic patterns. For systems with two or four confined electrons, strong absorption and fluorescence in the visible or even IR energ...

Structure and Formation of Luminescent Centers in Light-Up Ag Cluster-Based DNA Probes

“…Ten singlet excited states were calculated with TD-DFT, and five states were obtained using ADC(2) to establish the error of the TD-DFT method with regard to the more correct methods. The M06 functional was previously approved in comparison with the ADC(2) pure ab initio method. − The electronic excitation (absorption) spectra in the 516–300 nm band obtained in this work using M062X&def2-TZVP* agree well with the spectra calculated in the framework of ADC(2)&def2-TZVP* that is considered as a benchmark. − The spectra obtained using different approaches are presented in Table S9.…”

“…The M062x functional with the hybrid basis sets def2-SVP­[H]/def2-TZVP/def2-TZVPP­[Ag] (M062X&def2-TZVP*) was used to optimize Ag 4 @C 6 complexes, at a “high level”, and the rest of the nucleobases and deoxyribose-phosphate backbone were calculated by PBE0&SVP, at a “low level”. The M062x functional was approved earlier for silver–ligand complexes. − The final conventional optimization using the M062X&def2-SVP­[H,C,P]/def2-TZVP­[N,O]/def2-TZVPP­[Ag] approach was applied to the chromophore Ag 4 @C 6 complex, while the remaining molecular environment was frozen.…”

Silver Cluster Interactions with Tyrosine: Towards Amino Acid Detection

“…We have calculated the absorption spectra for the most energetically favorable complexes of silver NCs and Tyr. Geometry optimization has been performed with the MP2/6-31G(d,p),LANLTZ method, which has previously demonstrated high effectiveness on ligand-protected Ag NCs [ 48 ]. The first 10 transitions in the electronic absorption spectra have been calculated with TDDFT, in particular the M062X/def2-TZVP method, which has proved its efficacy in simulating the spectra of similar silver–organic systems [ 51 ].…”

“…We have calculated UV-vis absorption spectra for the most energetically favorable complexes. Since MP2 gives better geometry predictions for ligand-protected Ag NCs than DFT [ 48 ], we have established the MP2 geometries prior to absorption spectra calculation. The MP2 realized in Orca 3.0 has been used along with the 6-31G(d,p) basis set and LANLTZ ECP as before [ 38 ].…”

Excited States in Single-Stranded and i-Motif DNA with Silver Ions

“…Second-order Møller–Plesset perturbation theory with a resolution-of-identity approximation (RI-MP2) has been used for optimization of the complexes with various initial configurations of silver ions relative to the nucleobase ligands. Vertical excitation energies of the molecular systems have been calculated by means of the second-order algebraic diagrammatic construction ADC(2) scheme, which has been already used in our previous studies. − The hybrid basis sets def2-SVP­[H]/def2-TZVPP­[Ag]/def2-TZVP have been applied for both the procedures, where def2-SVP, def2-TZVPP, and def2-TZVP correspond to hydrogen, silver, and rest of the elements, respectively, but the cores of occupied MOs have been frozen below −3.0 hartree. , …”