Fu-Quan Bai

What Makes Hydroxamate a Promising Anchoring Group in Dye- Sensitized Solar Cells? Insights from Theoretical Investigation

We report, from a theoretical point of view, the first comparative study between the highly water-stable hydroxamate and the widely used carboxylate, in addition to the robust phosphate anchors. Theoretical calculations reveal that hydroxamate would be better for photoabsorption. A quantum dynamics description of the interfacial electron transfer (IET), including the underlying nuclear motion effect, is presented. We find that both hydroxamate and carboxylate would have efficient IET character; for phosphate the injection time is significantly longer (several hundred femtoseconds). We also verified that the symmetry of the geometry of the anchoring group plays important roles in the electronic charge delocalization. We conclude that hydroxamate can be a promising anchoring group, as compared to carboxylate and phosphate, due to its better photoabsorption and comparable IET time scale as well as the experimental advantage of water stability. We expect the implications of these findings to be relevant for the design of more efficient anchoring groups for dye-sensitized solar cell (DSSC) application.

Theoretical investigation on the photophysical properties of N-heterocyclic carbene iridium (III) complexes (fpmb)xIr(bptz)3-x (x = 1−2)

In the search for efficiently phosphorescent materials, this article presents a rational design and theoretical comparative study of some photophysical properties in the (fpmb)xIr(bptz)3‐x (x = 1–2), which involve the usage of two 2‐pyridyl triazolate (bptz) chromophores and a strong‐field ligand fpmb (fpmb = 1‐(4‐difluorobenzyl)‐3‐methylbenzimidazolium). The first principle theoretical analysis under the framework of the time‐dependent density functional theory approach is implemented in this article to investigate the electronic structures, absorption and phosphorescence spectra. It is intriguing to note that 1 and 2 exhibit theirs blue phosphorescent emissions with maxima at 504 and 516 nm, respectively. Furthermore, to obtain the mechanism of low phosphorescence yield in 1 and estimate the radiative rate constant kr for 2, we approximately measure the radiative rate constant kr, the spin‐orbital coupling (SOC) value, ΔE (S − T), and the square of the SOC matrix element (2) for 1 and 2. Finally, we tentatively come to conclusion that the switch of the cyclometalated ligand from the main to ancillary chelate seems to lower the splitting ΔE (S − T) in the current system.

DFT/TDDFT investigation of the electronic structures and optoelectronic properties of phosphorescent iridium (III) complexes with non-conjugated cyclometalated carbene ligands

This work investigates the electronic structures and spectroscopic properties of several cyclometalated iridium carbene complexes possessing at least one functionalized methylene moiety, (dfpmb)(dfbmb)Ir(mptz) (2), (dfbmb)2Ir(mptz) (3), and (dfbmb)2Ir(mpmtz) (4) (dfpmbH =1-difluorophenyl-3-methyl-benzimidazoline-2-ylidene; dfbmbHu2009=u20091-(2,4-difluorobenzyl)-3-(methylbenzimidazolium; mptzHu2009=u20094-methyl-2-(5-(trifluoromethyl)-2H-1,2,4-triazol-3-yl)pyridine); mpmtzHu2009=u20094-methyl-2-(3-methylene-5-(trifluoromethyl)- 2H-1,2,4-triazole-3-yl)pyridine) on the basis of their prototype (dfpmb)2Ir(mptz) (1) via DFT and TDDFT methods. A careful examination of results shows: (1) the patterns of the occupied orbitals for 1–4 are almost the same, with the HOMO being an admixture of the Ir atom and benzyl part, whereas the LUMO is predominately delocalized over the ancillary chelate mptz or mpmtz; (2) complexes 1–3, and especially 4, all exhibit blue emission with maximum wavelengths at 506, 495, 486, and 478u2009nm, respectively; (3) complex 4 with the highest (relative) component of 3MLCT can be reasonably expected to have a higher radiative transition rate constant (kr ) among 1–4. From the highest absorption peaks, eventually, the molar extinction coefficient discrepancy between experiment and calculations might be tentatively attributable to the synergism of the intrinsic imperfection of the PCM model and the simplification of chemical computations.

Dihydrogen bond in C2H4− n Cl n ··· NaH (n = 0, 1, 2, 3) complexes: ab initio, AIM and NBO studies

The dihydrogen-bonded complexes of ethylene and its chlorine derivatives with sodium hydride have been systematically investigated at the MP2/6-311++G(d,p) level. The studied complexes are divided into three groups (including Linear, Five- and Six-membered cyclic structures) based on the optimized structures. The structural, energetic and topological parameters are presented and analysed in terms of their possible correlation with the interaction energies and the intermolecular Hu2009···u2009H distances. The nature of the electrostatic interaction in this type of dihydrogen bond has also been unveiled by means of atoms in molecules (AIM) and natural bond orbital (NBO) analysis. The effect of ring structure on the dihydrogen bonding systems has been considered by comparing with the corresponding linear structure. NBO analysis suggests that the electron density transfer (EDT) in cyclic structures have dual-channel character.

Theoretical investigation of the adsorption, IR, and electron injection of hydroxamate anchor at the TiO2 anatase (1 0 1) surface

The adsorption of hydroxamate onto a TiO2 anatase surface has been theoretically determined. We find that the doubly deprotonated configuration is the optimal adsorption mode in terms of energetic and dynamical stability, which is demonstrated by vibrational spectrum analysis. This configuration can also undergo the ultrafast electron transfer event, with a time-scale of 53 fs.

TD-DFT investigation of electronic structures, photophysical properties and the theoretical design of OLEDs based on phosphorescent Ir(III) complexes bearing the non-π electron-conjugated carbene ligand

In the search for efficient phosphorescent materials, a rational design is presented for the iridium complex material (dfbmb)Ir(fptz)2 (2) (dfbmbu2009=u20091-(2,4-difluorobenzyl)-3-methylbenzimidazolium), which involves the use of two 2-pyridyl triazolate (fptz) chromophores and a non-π electron-conjugated high-field ligand dfbmb assembled by a saturated σ-bond methylene group, and a comparison with the benchmark (dfbmb)2Ir(fptz) (1). In this work the electronic structures, absorption and phosphorescence spectra were investigated using the TD-DFT method. In order to obtain the mechanism of high phosphorescence yield in (1) and estimate the radiative rate constant k r for (2), the radiative rate constant k r, the spin-orbital coupling (SOC) matrix element, ΔE(Su2009−u2009T), and the square of the SOC matrix element (⟨ψS1|HSO|ψT1⟩2) for (1) and (2) were measured. It is concluded that the switch of the cyclometalated ligand from the main chelate to the ancillary chelate seems to enhance the splitting of ΔE(Su2009−u2009T) in the current system. Finally, using the information gained, a PhOLED utilizing (1) and (2) was designed.

Exploring the sensitization properties of thienyl‐functionalized tripyrrole Ru(II) complexes on TiO2 (101) surface: a theoretical study

AbstractnRuthenium(II) complexes, as the dye sensitizer in the solar cell system, has attracted great interests. In the present study, based on the ruthenium(II) complex N749, new sensitizers have been designed theoretically to increase the stability and the efficiency of dye-sensitized solar cell (DSSC). By investigating the ground state geometries, electronic structures, and spectroscopic properties by density functional theory (DFT) and time-dependent DFT, the orbital components and absorption transition have been obtained. The effect of tripyrrin ligand in the designed new sensitizers can be demonstrated from our results. The results show that the absorption spectra are systematically broadened and red-shifted with the increase sizes of the pyrrole ligands. The important unoccupied orbitals referred to charge transfer are mainly from di/tripyrrin derivative groups. Consequently, the charge transfer to the di/tripyrrin derivative groups has been strengthened. According to our study, the di/tripyrrin derivative ligand is more efficient than the NCS− ligand in absorbing visible light. The calculation results also indicate that the electronic structures of the N749 derived sensitizers are significantly influenced by the different substituted positions of the thienyl groups on di/tripyrrin ligands. Thus, the efficiency of DSSCs would be different. Our research predicted that the Ru(II) complexes containing 5,10-(2-thienyl)-4,6,9,11-tripyrrin ligand may enhance the visible light absorption of DSSC. This is in accordance with the corresponding experiment. These results are expected to assist the molecular design for new dyes in future DSSCs.

Theoretical studies of heteroatom-doping in TiO2 to enhance the electron injection in dye-sensitized solar cells

Density functional calculations have been explored to analyze the structural, electronic and charge transfer properties of a doped TiO2 substrate and catechol–TiO2 interfaces for dye-sensitized solar cells. The results demonstrate that the dopant W6+ moves the CB (conduction band) edge downward and introduces 5d-unoccupied orbitals located in the CB bottom of the TiO2. On the other hand, the dopant Zn2+ shifts the CB edge upward with an insertion of 3d-occupied orbitals into the VB (valence band). In catechol–TiO2 systems, W6+ enlarges the energy difference between the LUMO of catechol and LUMO of TiO2, which enlarges the driving force for electron injection in turn and results in an increased short circuit current (Jsc). Our modeling injection dynamics and quantitative Bader analysis of the interfacial charge transfer have revealed that the catechol–TiO2 doped with W6+ provides faster and more electron injection for dye sensitized solar cells (DSSCs). While the Zn2+ doped system exhibits lower electron efficiency due to the minimized energy difference between the catechol LUMO and TiO2 CB.

Theoretical Studies on Structures and Spectroscopic Properties of Highly Efficient Phosphorescent [Ru(terpy)(phen)X]+ Complexes

The ground and the lowest-lying triplet excited state geometries, electronic structures, and spectroscopic properties of three mixed-ligand Ru(II) complexes [Ru(terpy)(phen)X]+ (terpy=2,2′,6′,2″-terpyridine, phen=1,10-phenanthroline, and X=—C≡CH (1), X=Cl (2), X=CN (3)) were investigated theoretically using the density functional theory method. The ground and excited state geometries have been fully optimized at the B3LYP/LanL2DZ and UB3LYP/LanL2DZ levels, respectively. The absorption and emission spectra of the complexes in CH3CN solutions were calculated by time-dependent density functional theory with the PCM solvent model. The calculated bond lengths of Ru—C, Ru—N, and Ru—Cl in the ground state agree well with the corresponding experimental results. The highest occupied molecular orbital were dominantly localized on the Ru atom and monodentate X ligand for 1 and 2, Ru atom and terpy ligand for 3, while the lowest unoccupied molecular orbital were π* (terpy) type orbital. Therefore, the lowest-energy a...