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.

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.

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.

Exploring the effect of aggregation-induced emission on the excited state intramolecular proton transfer for a bis-imine derivative by quantum mechanics and our own n-layered integrated molecular orbital and molecular mechanics calculations

We theoretically investigate the excited state intramolecular proton transfer(ESIPT) behavior of the novel fluorophore bis-imine derivative molecule HNP which was designed based on the intersection of 1-(hydrazonomethyl)-naphthalene-2-ol and 1-pyrenecarboxaldehyde. Especially, the density functional theory(DFT) and time-dependent density functional theory(TDDFT) methods for HNP monomer are introduced. Moreover, the "our own n-layered integrated molecular orbital and molecular mechanics"(ONIOM) method(TDDFT:universal force field(UFF)) is used to reveal the aggregation-induced emission(AIE) effect on the ESIPT process for HNP in crystal. Our results confirm that the ESIPT process happens upon the photoexcitation for the HNP monomer and HNP in crystal, which is distinctly monitored by the optimized geometric structures and the potential energy curves. In addition, the results of potential energy curves reveal that the ESIPT process in HNP will be promoted by the AIE effect. Furthermore, the highest occupied molecular orbital(HOMO) and lowest unoccupied molecular orbital(LUMO) for the HNP monomer and HNP in crystal have been calculated. The calculation demonstrates that the electron density decrease of proton donor caused by excitation promotes the ESIPT process. In addition, we find that the variation of atomic dipole moment corrected Hirshfeld population(ADCH) charge for proton acceptor induced by the AIE effect facilitates the ESIPT process. The results will be expected to deepen the understanding of ESIPT dynamics for luminophore under the AIE effect and provide insight into future design of high-efficient AIE compounds.

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.

ECD spectrometric methods for detecting the enantioselective enzymatic hydrolysis of racemic 3-acetoxy-4-phenyl-β-lactam

（-）-（3R, 4S）-3-Acetoxy-4-phenylazetidin-2-one （（-）-1） was the key intermediate for preparing optical C-13 side-chain moiety in partial synthesis of docetaxel and paclitaxel. It can be successfully prepared via enantioselective hydrolysis of racemic esters （（-4-）-1） catalyzed by bacterial lipases, but the current reaction evaluation method is tedious and inconvenient. Electronic circular dichroism （ECD） has been widely applied in the stereochemical study of chiral compounds. In this paper, a rapid ECD spectroscopic method has been proposed and established to detect the transformation directly. The absolute configurations of lipase-catalyzed hydrolysis products have also been confirmed by quantum-chemical calculation using time-dependent density functional theory （TDDFT） methodology.

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.

Mechanistic study of TPE-Ph COF for fluorescent ammonia detection

In this study,the interaction between TPE-Ph COF and ammonia molecules,as well as the mechanism of fluorescence detection of ammonia,were comprehensively investigated using density functional theory(DFT)and time-dependent density functional theory(TD-DFT).It was found that the binding between TPE-Ph COF and ammonia molecules occurs primarily through coordination bonds or hydrogen bonds.Specifically,the formation of coordination bonds significantly changes the intramolecular charge transfer of TPE-Ph COF,leading to fluorescence quenching.Computational analysis revealed the changes in electron and hole distributions upon the binding of ammonia to TPE-Ph COF,as well as the competition between nonradiative and radiative transitions during the photophysical processes,thereby elucidating the intrinsic mechanism of fluorescence response.

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.

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.