Theoretical Study on the Optical Properties for 2,7- and 3,6-Linked Carbazole Trimers by Time-dependent Density Functional Theory

Electronic properties, such as HOMO and LUMO energies, band gaps, ionization potential （IP） and electron affinity （EA） of 2,7- and 3,6-1inked carbazole trimers, two conjugated oligomcrs with different linkages of carbazole, were studicd by the density functional theory with Becke-Lee-Young-Parr composite exchange correlation functional （B3LYP）. The absorption spectra of these compounds were also investigated by time-dependent density functional theory （TD-DFT） with 6-3 IG＊ basis set. The calculated results indicated that the HOMO and LUMO of the 2,7- and 3,6-1inked carbazole trimers are both slightly destabilized on going from methyl substitution to sec-butyl substitution. Both IP and EA exhibit their good hole-transporting but poor electronaccepting ability. The presence of alkyl groups on the nitrogen atoms does not affect the intra-chain electronic delocalization along the molecular frame. Thus no significant effect on the band gap and absorption spectra of compounds has been found.

Investigation of Structural and Electronic Properties of [Tris(Benzene-1,2-Dithiolato)M]^3-(M = V, Cr, Mn, Fe and Co) Complexes: A Spectroscopic and Density Functional Theoretical Study

In this study, the first raw transition metals from V to Co complexes with benzene-1,2-dithiolate (L2-) ligand have been studied theoretically to elucidate the geometry, electronic structure and spectroscopic properties of the complexes. Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) methods have been used. The ground state geometries, binding energies, spectral properties (UV-vis), frontier molecular orbitals (FMOs) analysis, charge analysis and natural bond orbital (NBO) have been investigated. The geometrical parameters are in good agreement with the available experimental data. The metal-ligand binding energies are 1 order of magnitude larger than the physisorption energy of a benzene-1, 2-dthiolate molecule on a metallic surface. The electronic structures of the first raw transition metal series from V to Co have been elucidated by UV-vis spectroscopic using DFT calculations. In accordance with experiment the calculated electronic spectra of these tris complexes show bands at 522, 565, 559, 546 and 863 nm for V3+, Cr3+, Mn3+, Fe3+ and Co3+ respectively which are mainly attributed to ligand to metal charge transfer (LMCT) transitions. The electronic properties analysis shows that the highest occupied molecular orbital (HOMO) is mainly centered on metal coordinated sulfur atoms whereas the lowest unoccupied molecular orbital (LUMO) is mainly located on the metal surface. From calculation of intramolecular interactions and electron delocalization by natural bond orbital (NBO) analysis, the stability of the complexes was estimated. The NBO results showed significant charge transfer from sulfur to central metal ions in the complexes, as well as to the benzene. The calculated charges on metal ions are also reported at various charge schemes. The calculations show encouraging agreement with the available experimental data.

TD-DFT Study on Pyrazoline Derivatives

The molecular structures of ground state and first single excited state for pyrazoline derivatives are optimized with DFT B3LYP method and ab initio “configuration interaction with single excitations”（CIS） method, respectively. The frontier molecular orbital characteristics have been analyzed systematically, and the electronic transition mechanism has been discussed. Electronic spectra are calculated by using TD-DFT method. These results are consistent with those from the experiment.

Studies on Optical Properties of Si220 Nanoclusters viaTime-dependent Density Functional Theory Calculations

The optical properties of bare and hydrogen passivated Si220 nanoclusters（NCs） in four typical motifs（i.e.,bulk-like, onion-like, bucky-diamond and icosahedral motifs） were studied via time-dependent density functionaltheory（TD-DFT） calculations. The calculation results show that there is a significant blue shift in the optical absorp-tion spectra when the Si NCs are passivated with hydrogen. A strong absorption peak in the visible light region ap-years for the hydrogenated bulk-like, onion-like and bucky-diamond Si NCs.

Anisotropic Lattice Strain of Composite Materials of LiMnO2 and H/D-Substituted Chiral Cyanide-Bridged Ni（Ⅱ）-Fe（Ⅲ） Coordination Polymers

Composite materials composed of LiMnO2, a typical electrode material for lithium ion battery, and a chiral cyanide-bridged Ni（Ⅱ）-Fe（Ⅲ） coordination polymer [NiL2][Fe（CN）6]·4H2O （Ni-Fe, H-form） （L = （1R,2R）-（-）-1,2-cyclohexane-diamine） or its deuterium isomer, [NiL2][Fe（CN）6]·4D2O （Ni-Fe, D-form） have been prepared by the various ratios （w/w） of Ni-Fe：LiMnO2 = 10：0 （pure Ni-Fe）, 9：1, 8：2, 7：3, 6：4, 5：5, 4：6, 3：7, 2：8, 1：9 and 0：10 （pure LiMnO2）. Gradual shift of IR （infrared） spectra by changing the ratios and losing difference between H-form and D-form of Ni-Fe due to isotope effects revealed adsorption of Ni-Fe onto LiMnO2 to form composite materials. Formation of composite materials of Ni-Fe and LiMnO2 could be also proved losing ferromagnetic behavior of LiMnO2 on increasing of the ratios of Ni-Fe in each composite. In contrast to smoothly positive thermal expansion of pure LiMnO2 along the crystallographic b axis, variable temperature powder XRD （X-ray diffraction） patterns at 100-300 K of the composite materials exhibited thermally-accessible lattice distortion along the b axis with different ratios. It is also proved deviation of ideal linear correlation of an evaluation function, In K = a/T ＋ b （where, K = （d（T） - d（0））/d（T）, d（T） denotes nλ/（sin 2θ） at T （K））.

Redshift of Excitation Wavelength Caused by the Concentration of L-Tryptophan in Water: A Theoretical and Experimental Study

A redshift in the wavelength of excitation spectra is experimentally measured as a function of the concentration parameter for tryptophan solutions in water. To understand the microscopic causes of this behavior, theoretical calculations obtained from four model clusters are carried out: (Trp)1 - (H2O)9, (Trp)2 - (H2O)18, (Trp)3 - (H2O)27 and (Trp)4 - (H2O)36, where there are interactions among 1, 2, 3 and 4 molecules of tryptophan. According to the literature, each interaction occurred with nine molecules of water to stabilize its expected zwitterionic form. In these models, the molecules of tryptophan appear at an adjacent distance among them to generate an analogous behavior when there is an experimental increase in the concentration. It is evident that the distance between adjacent molecules of tryptophan decreases as their concentration increases. The optical properties of these clusters are obtained by studying the corresponding excited states and the molecular orbitals involved, showing charge transfers by using time-dependent density functional theory (TD-DFT) methods. The experimental spectroscopic data are obtained by using the clusters proposed, and good agreement is found by drawing a comparison with the theoretical data.

TD-DFT Accuracy in Determining Excited-state Structures and Fluorescence Spectra of Firefly Emitter

We analyzed the excited-state structures and emission spectra of firefly emitter, the anionic keto form of firefly oxyluciferin（keto-l）, determined by the time dependent-density functional theory（TD-DFT） approach. The analysis is based on a direct comparison with the highly correlated CASSCF（MS-CASPT2） ab initio approach. 49 DFT functionals were considered and applied to the study. Among the tested functionals, mPW3PBE, B3PW91 and B3P86 give the best performance for ground-state geometry, absorption spectrum, excited-state geometry and emis- sion spectrum.

TD-DFT Studies on Electronic and Spectral Properties of Platinum（II） Complexes with Phenol and Pyridine Groups

The molecular structures of the ground and the lowest triplet states for a series of Pt（ll） complexes PtLCl（l）[L=6-（2-hydroxyphenyl）-2,2＇-bipyridine], Pt（pp）2[pp=2-（2-hydroxyphenyl）pyridine]（2）, PtbpyClz（bpy=2,2＇- bipyridine）（3）, and the free tridentate L ligand（4） were optimized by the density functional theory B3LYP and UB3LYP methods, respectively. On the basis of optimized geometries, the spectral properties were investigated with time-dependent density functional theory（TD-DFT）. In comparison with those of complexes 2 and 3, the more rigid structure of complex 1 together with its low rate of the radiationless decay via nonemissive d-d state leads to higher photoluminescence quantum efficiency. And the phosphorescence quantum efficiency of complex 1 can be easily controlled by modifying auxiliary ligands. The introduction of fluorine ligand into complexes can effectively increase the radiation transition rate and decrease the radiationless d-d transition rate, and as a result, a novel complex PtLF（5） might be a good phosphorescent material suitable for organic electronic devices.

Theoretical studies of vibrationally resolved absorption and emission spectra: From a single chromophore to multichromophoric oligomers/aggregates

Absorption and photoluminescence spectroscopies are useful tools to study the photo-physical properties of materials. The theoretical methods for calculation of the spectra of molecules/supermolecules and aggregates, whose structures can differ significantly, are reviewed from the viewpoint of computational efficiency. Several model compounds/multimers are taken as examples for the spectral calculations. The numerical results achieve a satisfactory agreement between the theory and experiment.

Analyzing excited-state processes and optical signatures of a ratiomeric fluorine anion sensor: a quantum look

Recently, the spectroscopic signatures of a benzoselenadiazole derivative have been investigated in the framework of designing a new ratiometric fluoride sensor （Saravanan et al., Org Lett, 2014, 16： 354-357）. It was suggested that this sensor is un- dergoing excited-state intramolecular proton transfer. In this work, we provide a new look at these experimental data, using a state-of-the-art time-dependent density fimctiona/theory approach to mimic the spectroscopic signatures. New insights about the nature of the excited-state processes are obtained.

Theoretical studies on the spectroscopic properties and the substituent effects of pyridyl triazole Os(Ⅱ) complexes

To explore the spectroscopic properties of pyridyl triazole Os(Ⅱ) complexes and how the substituent effects affect the spectroscopic properties of [Os(ptz)2L2] (L=PH3; ptzH=(2-pyridyl)-1,2,4-triazole) (1), [Os(bptz)2L2] (bptzH=3-tert-butyl-5-(2-pyridyl)-1,2,4-triazole) (2), [Os(fptz)2L2] (fptzH=3- (trifluoreomethyl)- 5-(2-pyridyl)-1,2,4-triazole) (3), and [Os(fbtz)2L2] (fbtzH=3-(trifluoreomethyl)-5-(4-tert-butyl- 2-pyridyl)-1,2, 4-triazole) (4), the density functional theory (DFT) method at the B3LYP level was used to optimize the geometrical structures in the ground and excited state. The absorption and emission properties of the dichloromethane solution were predicted at the time-dependent density functional theory (TD-DFT, B3LYP) level associated with the PCM solvent effect model, the transitions characters of them were assigned. Important correlations between substituent effects and emission spectra and the quantum yield have been obtained by comparing and analyzing the calculated results.

Accurate Control of Deuterated Locations and Amount of Deep Blue Ir（dfpypy）epic for Phosphorescent Efficiency Enhancement： Evaluations from Theoretical Aspect

A well-known deep-blue emitting iridium（III） complex was selected for deuterium isotope effect evalua- tion, both on deuterated locations and numbers, through theoretical investigation. It was revealed that the containment of the d site deuteriation of ancillary ligand picolinate enabled the non-radiative deactivation process to be repessed, and thereby improving the quantum efficiency through such a simple and controllable approach.

A Series of Pure Orange-yellow Iridium Complexes with Low Efficiency Roll-off： a Computational Study

The electronic structures and spectroscopic properties of heteroleptic cyclometalated iridium（Ⅲ） complexes were investigated. The geometries, electronic structures, and the lowest-lying excited states of （DBQ）2Ir（acac） and （MDQ）2Ir（acac） were investigated via density functional theory-based approaches. A series of designed models of （DBQ）2Ir（dpis）, （DBQ）2Ir（tpip）, （MDQ）2Ir（dpis） and （MDQ）2Ir（tpip） was also calculated for comparison. The structures in the ground and excited states were optimized via B3LYP method. The lowest absorptions and emissions spectra were evaluated via TD-B3LYP and TD-PBE1PBE methods, The computational results reveal that the emission peaks of the designed complexes are at around 585-640 nm, which belong to the orange-yellow wavelength. The frontier molecular orbital properties indicate that the Ir（Ⅲ） complexes have low efficiency roll-off.