Effects of Halogen Substitution on Naphthazarin Tautomerism in the Ground and Excited States

5,8-Hihydroxyl-1,4-naphthazarin was taken as a model compound to explore the effect of halogen substitution on intramolecular proton transfer process. Calculations indicate that the substitution in the R2- and R4-positions far away from the active region has much weaker influence on the IPT process than that in the R1- and R3-positions. IPT barriers for substitution in the R1-position are higher than that of parent molecule. However, it is quite reverse for substitution in the R3-position. The IPT process is a proton transfer process coupled with charge separation and coulombic interaction would be dominant during this process. As for naphthazarin, halogen substitution would decrease the quantum yields of O2 but increase those of ^1O2.

Theoretical Study of the Isomerization Reaction of 1-3 H Transfer on Formamidine Substituted by Halogen

The ab initio method has been used to study the 1-3 H transfer reaction on formamidine substituted by halogen. The calculation results show that the substituted halogen has two effects on the 1-3 H transfer reaction: decreasing the activation energy and stabilizing the C=N double bond owing to the conjugative effect of p-π-p of products and transition states.

Halogen modified two-dimensional covalent triazine frameworks as visible-light driven photocatalysts for overall water splitting

The covalent triazine framework CTF-1 as a member of the two-dimensional covalent organic frameworks(COFs)is a category of novel metal-free photocatalysts for water splitting.The large band gap severely restricts its energy conversion efficiency.By means of the first-principles calculations,we proposed the decoration of CTF-1 by anchoring halogen atoms onto benzene moieties for improving the solar-to-hydrogen(STH)efficiency.The electronic structures reveal that the halogen substitution successfully decreases the band gap of CTF-1.Meanwhile,the calculated free energy changes along the reaction pathway indicate that all these COFs can spontaneously drive overall water splitting under light irradiation in a specific acid-base environment.The time-dependent ab initio non-adiabatic molecular dynamics simulations suggest that the electron-hole recombination periods of these COFs fall in a few to tens of nanoseconds.Excitingly,CTF-1 modified by linking six iodine atoms onto the benzene ring in the para-position(CTF-1-6I)shows a quite low band gap of 2.81 eV,indicating that it is a visible-light driven COF for overall photocatalytic water splitting.Correspondingly,CTF-1-6I also exhibits an extraordinarily promising STH efficiency of 3.70%,which is an order magnitude higher than that of the pristine CTF-1.

A gram-scale synthesis of multi-substituted arenes via palladium catalyzed C–H halogenation

（6-Amino-2-chloro-3-fluorophenyl）methanol is prepared through both traditional methods and palladium catalyzed iterative C–H halogenation reactions.In comparison to traditional approach,the C–H functionalization strategy demonstrated a few advantages including milder reaction conditions higher yields,better selectivity and practicality,and high chemical diversity.

A hybrid organic-inorganic perovskite with robust SHG switching

Owing to the diversity of structure and potential applications in the field of electrics,sensors,and light-emitting diodes,lead halide perovskites have attracted great attention in recent years.Especially those lead halide perovskites with non-centrosymmetric crystal structures usually exhibit nonlinear optical(NLO) characteristics,which may endow them photoelectricity switching functionality.In this work,a lead-based hybrid organic-inorganic perovskite(HOIP) material,trimethyliodomethylammonium lead trichloride(TMIM·PbCl_(3)),is obtained on the basis of tetramethylammonium lead chloride through halogen substitution on the cation part.It shows dual-phase-transition behavior around 345 and 358 K, which is significantly improved.TMIM·PbCl_(3)crystallizes in the chiral space group,P2_(1)2_(1)2_(1), and shows a welldefined second harmonic generation(SHG) response,and good switching endurance,which makes it an excellent candidate for SHG switching material.This work highlights the importance of halogen substitution for crystal engineering and may pave way for the further exploration of the optoelectronic devices.

Energy transfer process of Nd^(3+)/Ho3+co-doped fluoride halide glasses with anion substituted multi-wavelength tunable mid-infrared luminescence

Ho^(3+)doped ZBLAN glass with 2.0 and 2.9μm emission was prepared.In order to further improve the luminescence of Ho^(3+),halogen ions(Cl,Br,1)were introduced to reduce the maximum phonon energy and phonon state density of the sample.At the same time,Nd^(3+)was introduced to transfer the energy to Ho^(3+)pumped with a 793 nm laser(Nd^(3+):4 F5/2,4 F3/2→Ho^(3+):5 I6).The effect of different halogen ion on the luminescent properties of the fluoride halide glass was compared.The results show that the luminescent intensity of infrared increases with the introduction of different halogen ions.By comparison,it is found that the sample with I-has the strongest luminescence of 1064 nm,2.0μm and 2.9μm.This is consistent with the calculated J-O intensity parameters.In addition,the 2.0 and 2.9μm emission of Ho^(3+)pumped with a 450 nm laser will not disappear.A mid-infrared sample with multi-wavelength excitation and multi-wavelength emission can be obtained.Nd^(3+)/Ho^(3+)co-doped fluoride halide glasses with 1064 nm,2.0μm and 2.9μm luminescence were prepared by melt quenching method.The luminescent mechanism and the energy transfer process between the two ions of Nd^(3+)/Ho^(3+)co-doped fluoride halide glass were studied.The J-O parameters,luminescence lifetime and absorption emission cross-sectional area of Ho^(3+)and Nd^(3+)were calculated,respectively.It is found that the value ofΩ2 in the glass matrix increases with the introduction of different halogen ions,whileΩ4 andΩ6 do not change obviously in different glass compositions.This is because the environment of the crystal field around the rare earth ions changes.The crystal phase and phonon energy of the sample were analyzed by X-ray diffraction pattern and a Fourier transform infrared spectrometer,respectively.Based on the above spectra and data(phonon energy is 634.71 cm-1),it can be predicted that Nd^(3+)/Ho^(3+)co-doped fluoride halide glass is a potential mid-infrared luminescent material.