Excited-state proton-transfer reactions of 7-azaindole with water, ammonia and mixed water–ammonia: microsolvated dynamics simulation

<div><p>Dynamics simulations of excited-state multiple proton transfer (ESMPT) reactions in 7-azaindole (7AI) with ammonia, mixed water–ammonia, and water molecules were investigated by quantum dynamics simulations in the first-excited state using RI-ADC(2)/SVP-SV(P) in the gas phase. 7AI(WW), 7AI(WA), 7AI(AW) and 7AI(AA) clusters (W, water and A, ammonia) show very high probability of the excited-state triple proton transfer (ESTPT) occurrence in ranges from 20% for 7AI(WA) to 60% for 7AI(AW), respectively. Furthermore, 7AI(AW) clusters with ammonia placed near N–H of 7AI has the highest probability among other isomers. In 7AI with three molecules of bridged-planar of water, ammonia and mixed water–ammonia clusters, the excited-state quadruple proton transfer reactions occur ineffectively and rearrangement of hydrogen-bonded network on solvents also takes place prior to either ESTPT or excited-state double proton transfer. The role played by mixed-solvent is revealed with replacing H₂O with NH₃ in which the ESMPT is found to be more efficient corresponding to lower barrier in the excited state. The preferential number of solvent surrounding 7AI that facilitates the proton transfer process is two for methanol and water but this preferential number for ammonia is one.</p><p>Highlights: (i) replacing H₂O with NH₃ assists ESPT corresponding to lower barrier in the excited state; (ii) the ESMPT time of 7AI with mixed water–ammonia is in the sub-picosecond timescale; (iii) the PT tends to be concerted process with at least one ammonia, but synchronous without ammonia.</p></div

Heteroatom substitution effect on electronic structures, photophysical properties, and excited-state intramolecular proton transfer processes of 3-hydroxyflavone and its analogues: A TD-DFT study

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Theoretical Investigation on the Electronic and Optical Properties of Poly(fluorenevinylene) Derivatives as Light-Emitting Materials

Density functional theory (DFT) and time-dependent DFT (TDDFT) were employed to study ground-state properties, HOMO-LUMO gaps (ΔH-L), excitation energies (Eg), ionization potentials (IPs), and electron affinities (EA) for PFV-alt-PDONV and PFV-alt-PDIH-PPV having different alternating groups. Excited-state properties were investigated using configuration interaction singles (CISs) while fluorescence energies were calculated using TDDFT. The results show that PFV-alt-PDONV exhibits blue-shifted energies for both HOMO-LUMO gaps (ΔH-L) and excitation energies (Eg) compared with PFV-alt-PDIH-PPV. The predicted IP and EA clearly indicate that PFV-alt-PDIH-PPV has both easier hole creation and electron injection than that of PFV-alt-PDONV. The maximal absorption wavelengths of all polymers are strongly assigned to π→π∗ transition. The predicted radiative lifetimes of PFV-alt-PDONV and PFV-alt-PDIH-PPV for B3LYP/6-31G(d) are 0.36 and 0.61 ns, respectively, indicating that PFV-alt-PDIH-PPV should have a better performance for long-time emission than that of PFV-alt-PDONV

Theoretical Insight into Catalytic Propane Dehydrogenation on Ni(111)

Here, propane dehydrogenation (PDH) to propylene and side reactions, namely, cracking and deep dehydrogenation on Ni(111) surface, have been theoretically investigated by density functional theory calculation. On the basis of adsorption energies, propane is physisorbed on Ni(111) surface, whereas propylene exhibits chemisorption supported by electronic charge results. In the PDH reaction, possible pathways can occur via two possible intermediates, i.e., 1-propyl and 2-propyl. Our results suggest that PDH reaction through 1-propyl intermediate is both kinetically and thermodynamically more favorable than another pathway. The C–C bond cracking during PDH process is more difficult to occur than the C–H activation reaction because of higher energy barrier of the C–C bond cracking. However, deep dehydrogenation is the preferable process after PDH, owing to the strong adsorption of propylene on Ni(111) surface, resulting in low selectivity of propylene production. This work suggests that Ni(111) has superior activity toward PDH; however, the enhancement of propylene desorption is required to improve its selectivity. The understanding in molecular level from this work is useful for designing and developing better Ni-based catalysts in terms of activity and selectivity for propane conversion to propylene

Excited-state intermolecular proton transfer reactions of 7-azaindole(MeOH)(n) (n = 1-3) clusters in the gas phase: on-the-fly dynamics simulation.

MEDLINE:22026497International audienceUltrafast excited-state intermolecular proton transfer (PT) reactions in 7-azaindole(methanol)(n) (n = 1-3) [7AI(MeOH)(n=1-3)] complexes were performed using dynamics simulations. These complexes were first optimized at the RI-ADC(2)/SVP-SV(P) level in the gas phase. The ground-state structures with the lowest energy were also investigated and presented. On-the-fly dynamics simulations for the first-excited state were employed to investigate reaction mechanisms and time evolution of PT processes. The PT characteristics of the reactions were confirmed by the nonexistence of crossings between S(pipi*) and S(pisigma*) states. Excited-state dynamics results for all complexes exhibit excited-state multiple-proton transfer (ESmultiPT) reactions via methanol molecules along an intermolecular hydrogen-bonded network. In particular, the two methanol molecules of a 7AI(MeOH)(2) cluster assist the excited-state triple-proton transfer (ESTPT) reaction effectively with highest probability of PT

Effect of Water Microsolvation on the Excited-State Proton Transfer of 3-Hydroxyflavone Enclosed in γ-Cyclodextrin

The effect of microsolvation on excited-state proton transfer (ESPT) reaction of 3-hydroxyflavone (3HF) and its inclusion complex with γ-cyclodextrin (γ-CD) was studied using computational approaches. From molecular dynamics simulations, two possible inclusion complexes formed by the chromone ring (C-ring, Form I) and the phenyl ring (P-ring, Form II) of 3HF insertion to γ-CD were observed. Form II is likely more stable because of lower fluctuation of 3HF inside the hydrophobic cavity and lower water accessibility to the encapsulated 3HF. Next, the conformation analysis of these models in the ground (S0) and the first excited (S1) states was carried out by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, respectively, to reveal the photophysical properties of 3HF influenced by the γ-CD. The results show that the intermolecular hydrogen bonding (interHB) between 3HF and γ-CD, and intramolecular hydrogen bonding (intraHB) within 3HF are strengthened in the S1 state confirmed by the shorter interHB and intraHB distances and the red-shift of O–H vibrational modes involving in the ESPT process. The simulated absorption and emission spectra are in good agreement with the experimental data. Significantly, in the S1 state, the keto form of 3HF is stabilized by γ-CD, explaining the increased quantum yield of keto emission of 3HF when complexing with γ-CD in the experiment. In the other word, ESPT of 3HF is more favorable in the γ-CD hydrophobic cavity than in aqueous solution

Cavity Closure of 2-Hydroxypropyl-β-Cyclodextrin: Replica Exchange Molecular Dynamics Simulations

2-Hydroxypropyl-&beta;-cyclodextrin (HP&beta;CD) has unique properties to enhance the stability and the solubility of low water-soluble compounds by inclusion complexation. An understanding of the structural properties of HP&beta;CD and its derivatives, based on the number of 2-hydroxypropyl (HP) substituents at the &alpha;-d-glucopyranose subunits is rather important. In this work, replica exchange molecular dynamics simulations were performed to investigate the conformational changes of single- and double-sided HP-substitution, called 6-HP&beta;CDs and 2,6-HP&beta;CDs, respectively. The results show that the glucose subunits in both 6-HP&beta;CDs and 2,6-HP&beta;CDs have a lower chance of flipping than in &beta;CD. Also, HP groups occasionally block the hydrophobic cavity of HP&beta;CDs, thus hindering drug inclusion. We found that HP&beta;CDs with a high number of HP-substitutions are more likely to be blocked, while HP&beta;CDs with double-sided HP-substitutions have an even higher probability of being blocked. Overall, 6-HP&beta;CDs with three and four HP-substitutions are highlighted as the most suitable structures for guest encapsulation, based on our conformational analyses, such as structural distortion, the radius of gyration, circularity, and cavity self-closure of the HP&beta;CDs