具有Cn对称性的大分子的能带结构研究 1: 计算方法

利用环间和环内Bloch函数建立了一组新的原子轨道基函数。首次设计了适用于一维具有旋转对称性的大环分子的能带程序。计算了酞菁、四氮卟吩、四苯并卟啉, 四苯基卟啉的能带结构, 较好地解释了卟啉类化合物导电性能不如酞菁类的事实。还计算了酞菁铜和酞菁锰的能带结构, 讨论了酞菁与酞菁简化模型的能带结构以及晶体轨道的差异。     

Control of emission by intermolecular fluorescence resonance energy transfer and intermolecular charge transfer

Control of emission by intermolecular fluorescence resonant energy transfer (IFRET) and intermolecular charge transfer (ICT) is investigated with the quantum-chemistry method using two-dimensional (2D) and three-dimensional (3D) real space analysis methods. The work is based on the experiment of tunable emission from doped 1,3,5-triphenyl-2-pyrazoline (TPP) organic nanoparticles (Peng, A. D.; et al. Adv. Mater. 2005, 17, 2070). First, the excited-state properties of the molecules, which are studied (TPP and DCM) in that experiment, are investigated theoretically. The results of the 2D site representation reveal the electron-hole coherence and delocalization size on the excitation. The results of 3D cube representation analysis reveal the orientation and strength of the transition dipole moments and intramolecular or intermolecular charge transfer. Second, the photochemical quenching mechanism via IFRET is studied (here "resonance" means that the absorption spectrum of TPP overlaps with the fluorescence emission spectrum of DCM in the doping system) by comparing the orbital energies of the HOMO (highest occupied molecular orbital) and the LUMO (lowest unoccupied molecular orbital) of DCM and TPP in absorption and fluorescence. Third, for the DCM-TPP complex, the nonphotochemical quenching mechanism via ICT is investigated. The theoretical results show that the energetically lowest ICT state corresponds to a pure HOMO-LUMO transition, where the densities of the HOMO and LUMO are strictly located on the DCM and TPP moieties, respectively. Thus, the lowest ICT state corresponds to an excitation of an electron from the HOMO of DCM to the LUMO of TPP.     

Novel Method for the Fabrication of a Charge‐Transfer Complex Crystal by Photoirradiation

A novel method for the fabrication of a charge‐transfer complex crystal was developed. Photoirradiation of a solution of TPP[Co(tbp)(CN)₂] and TPP[Co(Pc)(CN)₂] (tbp=tetrabenzoporphyrin, Pc=phthalocyanine, TPP=tetraphenylphosphonium) gave a molecular conducting crystal of a charge‐transfer complex TPP[Co(tbp)(CN)₂]₂, which was produced by the process in which the photoexcited electron in tbp was transferred from the LUMO of tbp to that of Pc.     

ESR study of molecular dynamics and orientation of TEMPO included in organic 1-D nanochannel

A mixture of 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) radical and 2,2,6,6-tetramethyl-1-piperidine (TEMP) was included into organic 1-D nanochannels of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) crystal. Dilution of the paramagnetic TEMPO radical was achieved with excess TEMP, thereby isolating a TEMPO molecule in the nanochannel. For inclusion compounds of TPP with TEMPO and TEMP (TEMPO/all guest compounds = 0.017, and 0.15), temperature-dependent electron spin resonance (ESR) spectra were observed to investigate their molecular dynamics and orientation. In the temperature range from 112 K to room temperature, the spectra depended remarkably on the temperature. Temperature dependence was well interpreted by uniaxial rotation, suggesting that TEMPO molecules undergo uniaxial rotation about a channel axis with a molecular orientation in which the N-O bond in the nitroxide group is perpendicular to the channel axis. The activation energy of uniaxial rotation was evaluated as 4.5 +/- 0.3 kJ mol(-1).     

Preliminary communication 13C CPMAS NMR of 5,10,15,20-tetrakis(4-n-dodecylphenyl)-porphyrin: dynamics of aliphatic chains in discotic lamellar mesophases

Solid state ¹³C CPMAS NMR spectra of 5,10,15,20-tetrakis(4-n-dodecylphenyl)porphyrin (C₁₂ TPP) have been studied to elucidate the microscopic structures and dynamics in the mesophases. The temperature dependence of ¹³C CPMAS NMR in the aliphatic regions is discussed mainly in relation to the phase transitions. The spectra for the aliphatic chains showed remarkable changes with the phase transition from crystal to lower mesophase (M_L) and from lower to higher mesophase (M_L). It was found that the aliphatic chains partially melt in the M_L phase, while they melt totally in the M_L phase. The spectra in the aromatic region did not vary greatly with the transitions from crystal to M_L and from M_L to M_L, which probably means that the molecular D_4h symmetries are distorted in these mesophases, as in the crystal, on the time scale observed by NMR (~kHz).     

Time-resolved electron spin resonance of gallium and germanium porphyrins in the excited triplet state

Gallium and germanium porphyrin complexes in the lowest excited triplet (T1) state have been studied by time-resolved electron spin resonance (TRESR). It is found that for Ge(TPP)(OH)2 (TPP = dianion of tetraphenylporphyrin) intersystem crossing (ISC) from the lowest excited singlet (S1) state to the T1x and T1y sublevels is faster than that to the T1z sublevel (T1x, T1y, and T1z are sublevels of the T1 state), while the ISC of ZnTPP and Ga(TPP)(OH) is selective to the T1z sublevel. This is interpreted by a weak interaction between the dpi orbital of germanium and LUMO (eg) of the porphyrin ligand, resulting in small spin-orbit coupling (SOC). The interpretation is supported by molecular orbital calculations. The ISC of Ge(OEP)(OH)2 (OEP = dianion of octaethylporphyrin) and Ge(Pc)(OH)2 (Pc = dianion of tetra-tert-butylphthalocyanine) is found to be selective to the T1z sublevel in contrast to Ge(TPP)(OH)2. This dependence on the porphyrin ligand is reasonably explained by a difference between the 3(a(1u)eg) (the OEP and Pc complexes) and 3(a(2u)eg) (the TPP complex) configurations. This is the first observation of a difference in selective ISC between the 3(a(1u)eg) and 3(a(2u)eg) configurations. The TRESR spectrum of Ge(TPP)Br2 is different from those of Ge(TPP)Cl2 and Ge(TPP)(OH)2, and is interpreted by SOC between the T1 and T2 states. From ESR parameters the square of the coefficient of the eg orbital on bromine is evaluated as 0.018 in the T1 state.     

Wavelength-dependent electron and energy transfer pathways in a side-to-face ruthenium porphyrin/perylene bisimide assembly

A new side-to-face supramolecular array of chromophores, where a pyridyl-substituted perylene bisimide dye axially binds to two ruthenium porphyrin fragments, has been prepared by self-assembly. The array is formulated as DPyPBI[Ru(TPP)(CO)](2), where DPyPBI = N,N'-di(4-pyridyl)-1,6,7,12-tetra(4-tert-butylphenoxy)perylene-3,4:9,10-tetracarboxylic acid bisimide and TPP = 5,10,15,20-tetraphenylporphyrin. The photophysical behavior of DPyPBI[Ru(TPP)(CO)](2) has been studied by fast (nanoseconds) and ultrafast (femtoseconds) time-resolved techniques. The observed behavior sharply changes with excitation wavelength, depending on whether the DPyPBI or Ru(TPP)(CO) units are excited. After DPyPBI excitation, the strong fluorescence typical of this unit is completely quenched, and time-resolved spectroscopy reveals the occurrence of photoinduced electron transfer from the ruthenium porphyrin to the perylene bisimide dye (tau = 5.6 ps) followed by charge recombination (tau = 270 ps). Upon excitation of the Ru(TPP)(CO) fragments, on the other hand, ultrafast (tau < 1 ps) intersystem crossing is followed by triplet energy transfer from the ruthenium porphyrin to the perylene bisimide dye (tau = 720 ps). The perylene-based triplet state decays to the ground state on a longer time scale (tau = 9.8 micros). The photophysics of this supramolecular array provides remarkable examples of (i) wavelength-dependent behavior (a small change in excitation wavelength causes a sharp switch from electron to energy transfer) and (ii) intramolecular sensitization (the triplet state of the perylene bisimide, inaccessible in the free dye, is efficiently populated in the array).     

Effective enhancement of the emission efficiency of tetraphenylporphyrin in solid state by tetraphenylethene modification

Evidently enhanced red emission efficiency from the solid state of tetraphenylporphyrin derivative was achieved by modification with tetraphenylethene units.     

磷酸三苯酯对聚对苯二甲酸乙二酯结晶速率的影响

用光学退偏振法和DSC方法研究了聚合过程的助剂磷酸三苯酯(TPP)对聚对苯二甲酸乙二酯(PET)结晶速率的影响。用熔融混入办法将磷酸三苯酯加入PET中,不能降低PET在靠近T_g的低温结晶区的结晶速率。TPP对PET结晶速率影响的特点表明它不是PET的成核剂,而是一个增塑剂。加入TPP后样品的结晶速率可根据T_m和T_g的移动,从纯PET的结晶速率来预测。     

Structural basis of thiamine pyrophosphate analogues binding to the eukaryotic riboswitch

The thiamine pyrophosphate (TPP)-sensing riboswitch is the only riboswitch found in eukaryotes. In plants, TPP regulates its own production by binding to the 3' untranslated region of the mRNA encoding ThiC, a critical enzyme in thiamine biosynthesis, which promotes the formation of an unstable splicing variant. In order to better understand the molecular basis of TPP-analogue binding to the eukaryotic TPP-responsive riboswitch, we have determined the crystal structures of the Arabidopsis thaliana TPP-riboswitch in complex with oxythiamine pyrophosphate (OTPP) and with the antimicrobial compound pyrithiamine pyrophosphate (PTPP). The OTPP-riboswitch complex reveals that the pyrimidine ring of OTPP is stabilized in its enol form in order to retain key interactions with guanosine 28 of the riboswitch previously observed in the TPP complex. The structure of PTPP in complex with the riboswitch shows that the base moiety of guanosine 60 undergoes a conformational change to cradle the pyridine ring of the PTPP. Structural information from these complexes has implications for the design of novel antimicrobials targeting TPP-sensing riboswitches.     

Uncommon Intramolecular Charge Transfer Effect and Its Potential Application in OLED Emitters

Planarized intramolecular charge transfer(PLICT)state can facilitate the fluorescence process thanks to the relative excellent planarity.Recently,we have discovered that the excited state quinone-conformation induced planarization(ESQIP)occurring on tetraphenylpyrazine(TPP)based derivatives could furnish them with PLICT feature.Unlike to the well-known intramolecular charge transfer,strengthening the electron-donating nature on the donor(D)moiety did not impair the PLICT.The calculation results showed that planarization of the TPP based compounds scarcely accompanied with energy wastage while amount of energy was required for the torsion on geometries.In the polar solvents,the energy consumption for planarization could further decrease,but that for twisting structure would increase.To take advantage of the transformation of the frontier orbitals'distribution,the PLICT type materials would perform a potential application on organic light-emitting diodes(OLEDs).     

四苯基卟吩化合物的表面增强喇曼散射

自首次发现表面增强喇曼散射(SERS)并计算了其增强倍数后,现已发展成为一个十分活跃的研究领域,并先后采取金属电极、真空镀膜、银溶胶等方法达到增强的目的.本文采用化学还原镀银法研究了四苯基卟吩(简称TPP)系列化合物在银表面的SERS。TPP类化合物尽管边缘取代物有很大差别,但其中心核相似.某些TPP类化合物的共振喇曼谱和红外光谱已有过报导。本文讨论了TPP金属络合物与自由碱基TPP化合物在SERS中存在差别的原因,提出了TPP化合物在银表面的吸附态,探讨了SERS的增强机理。     

Molecular and ionic complexes of pyrrolidinofullerene bearing chelating 3-pyridyl units

Molecular and ionic complexes of cis-2',5'-di(pyridin-3-yl)pyrrolidino[3',4':1,9](C(60)-I(h))[5,6]fullerene DP3FP with chlorobenzene (C(6)H(5)Cl), manganese(II) tetraphenylporphyrin (Mn(II)TPP) and tetrakis(dimethylamino)ethylene (TDAE) have been obtained for the first time. X-ray single crystal structure determination for the crystalline DP3FP·C(6)H(5)Cl (1) solvate proved unambiguously its molecular structure with the cis-arrangement of chelating 3-pyridyl groups. It has been demonstrated that DP3FP easily forms self-assembled photoactive complexes with metallated porphyrins. For example, the formation of a 1 : 1 complex between DP3FP and zinc (II) tetraphenylporphyrin (Zn(II)TPP) in cyclohexane solution (2) was evidenced using absorption spectroscopy. A successful X-ray single crystal structure determination was performed for a self-assembled triad composed of a DP3FP molecule linked with two Mn(II)TPP molecules in {DP3FP·(Mn(II)TPP)(2)}·(C(6)H(4)Cl(2))(3) (3). A strong organic donor TDAE reduces DP3FP to the radical anion state thus forming an ionic complex (TDAE˙(+))·(DP3FP˙(-))·(C(6)H(4)Cl(2))(1.6) (4). Optical, electronic and magnetic properties of 4 were investigated in detail. The performed studies strongly suggest that pyrrolidinofullerene DP3FP can be used as a building block in the design of various organic materials with advanced optoelectronic and/or magnetic properties.     

基于分子内荧光能量转移的碘聚合膜荧光传感器

合成了基于分子内荧光能量转移的蒽（An）-四苯基卟啉（TPP）双发色团碘荧光探针1．由于An的荧光光谱与TPP的S吸收带具有较好的重叠,供体An与受体TPP之间可以发生有效的分子内荧光能量转移,以An的最大吸收波长作为激发波长时,由于分子内荧光能量转移,受体TPP发出荧光．当碘与探针分子中的识别基团An作用时,导致探针分子的荧光转导基团TPP荧光淬灭．与An、TPP和An＋TPP混合物作敏感材料相比,将探针1固定在PVC膜中制备的敏感膜对碘选择性高、灵敏度好．另外,敏感膜具有很好的重现性、可逆性和稳定性,响应时间小于60S．除Cr2O7^2-和MnO4^-外,食品中常见的无机离子和可能存在的干扰物质不影响碘的测定．在最优条件下,传感器的线性范围为2．04×10^-6-2．36×10^-2mol／L,检出限为3．30×10^-8mol／L．本方法应用于加碘食盐中碘含量的测定,结果满意．     

One-Pot Functionalization of Graphene with Porphyrin through Cycloaddition Reactions

Two types of graphene‐based hybrid materials, graphene‐TPP (TPP=tetraphenylporphyrin) and graphene‐PdTPP (PdTPP=palladium tetraphenylporphyrin), were prepared directly from pristine graphene through one‐pot cycloaddition reactions. The hybrid materials were characterized by thermogravimetric analysis (TGA), by TEM, by UV/Vis, FTIR, Raman, and luminescence spectroscopy, and by fluorescence/phosphorescence lifetime measurements. The presence of the covalent linkages between graphene and porphyrin was confirmed by FTIR and Raman spectroscopy and further supported by control experiments. The presence of TPP (or PdTPP) in the hybrid material was demonstrated by UV/Vis spectroscopy, with TGA results indicating that the graphene‐TPP and graphene‐PdTPP hybrid materials contained approximately 18 % TPP and 20 % PdTPP. The quenching of fluorescence (or phosphorescence) and reduced lifetimes suggest excited state energy/electron transfer between graphene and the covalently attached TPP (or PdTPP) molecules.     

Effect of zeolite properties on ground-state and triplet-triplet absorption, prompt and oxygen induced delayed fluorescence of tetraphenylporphyrin at gas/solid interface

The ground-state and transient absorption, prompt and delayed fluorescence of tetraphenylporphyrin (TPP) adsorbed onto the external surface of different zeolites was monitored using diffuse-reflectance steady-state and laser flash photolysis. The delayed fluorescence (DF) of TPP detected in the presence of O2 is attributed to the energy transfer from 3TPP to 3O2 to form 1O2 and subsequent energy transfer from 1O2 to some other 3TPP within the organised molecular ensembles on the zeolite surface. The spectroscopic and kinetic parameters, namely the yield of DF (2-20% relative to prompt fluorescence), depend on the zeolite properties: the observed differences were correlated with the acid-base properties of the two zeolite series studied in this work (KA, NaA, CaA) and (NaA, NaX, NaY).     

A concerted approach for the determination of molecular conformation in ordered and disordered materials

We present the successful application of a concerted approach for the investigation of the local environment in ordered and disordered phases in the solid state. In this approach we combined isotope labeling with computational methods and different solid-state NMR techniques. We chose triphenylphosphite (TPP) as an interesting example of our investigations because TPP exhibits two crystalline modifications and two different amorphous phases one of which is highly correlated. In particular we analyzed the conformational distribution in three of these phases. A sample of triply labeled 1-[13C]TPP was prepared and 1D MAS as well as wide-line 13C NMR spectra were measured. Furthermore we acquired 2D 13C wide-line exchange spectra and used this method to derive highly detailed information about the phenyl orientation in the investigated TPP phases. For linkage with a structure model a DFT analysis of the TPP molecule and its immediate environment was carried out. The ab initio calculations of the 13C chemical shift tensor in three- and six-spin systems served as a base for the calculation of 1D and 2D spectra. By comparing these simulations to the experiment an explicit picture of all phases could be drawn on a molecular level. Our results therefore reveal the high potential of the presented approach for detailed studies of the mesoscopic environment even in the challenging case of amorphous materials.     

Comparison of conformer distributions in the crystalline state with conformational energies calculated by ab initio techniques

Summary The conformational preferences of 12 molecular substructures in the crystalline state have been determined and compared with those predicted for relevant model compounds by ab initio molecular orbital calculations. Least-squares regression shows that there is a statistically significant correlation between the crystal-structure conformer distributions and the calculated potential-energy differences, even though the calculations relate to a gas-phase environment. Torsion angles associated with high strain energy (>1 kcal mol^-1) appear to be very unusual in crystal structures and, in general, high-energy conformers are underrepresented in crystal structures compared with a gas-phase, room-temperature Boltzmann distribution. It is concluded that crystal packing effects rarely have a strong systematic effect on molecular conformations. Therefore, the conformational distribution of a molecular substructure in a series of related crystal structures is likely to be a good guide to the corresponding gas-phase potential energy surface.     

Intermediate state during the crystal transition in aspartame, studied with thermal analysis, solid-state NMR, and molecular dynamics simulation

Aspartame (L-alpha-aspartyl-L-phenylalanine methyl ester) is a dipeptide sweetener about 200 times as sweet as sugar. It exists in crystal forms such as IA, IB, IIA, and IIB, which differ in crystal structure and in the degree of hydration. Among these, IIA is the most stable crystal form, and its crystal structure has been well determined (Hatada et al., J. Am. Chem. Soc., 107, 4279-4282 (1985)). To elucidate the structural factors of thermal stability in the IIA form of aspartame and to examine the physical process in the crystal transformation between the IIA and IIB forms, we performed a thermal analysis and solid-state NMR measurements. We found that a quasi-stable intermediate state exists in the transformation, and it has the same crystal lattice as the usual IIA form, despite the dehydration from 1/2 mol to 1/3 mol per 1 mol of aspartame. The results of the energy component analysis and the molecular dynamics simulation suggest that the entropic effect promotes the generation of the intermediate state, which is presumably caused by the evaporation of the water of crystallization and the increase of molecular motion in aspartame. Thus, the thermal stability of the IIA form is attributable to a structural property, i.e., the crystal lattice itself is retained during the above dehydration. Moreover, the molecular dynamics simulations suggest that the aspartame molecules have two kinds of conformational flexibility in the intermediate state.     

Complexation of diphenyl(phenylacetenyl)phosphine to rhodium(III) tetraphenyl porphyrins: synthesis and structural,spectroscopic, and thermodynamic studies

The coordination of diphenyl(phenylacetenyl)phosphine (DPAP, 1) to (X)Rh(III)TPP (X = I (2) or Me (3); TPP = tetraphenyl porphyrin) was studied in solution and in the solid state. The iodide is readily displaced by the phosphine, leading to the bis-phosphine complex [(DPAP)(2)Rh(TPP)](I) (4). The methylide on rhodium in 3 is not displaced, leading selectively to the mono-phosphine complex (DPAP)(Me)Rh(TPP) (5). The first and second association constants, as determined by isothermal titration calorimetry and UV-vis titrations, are in the range 10(4)-10(7) M(-1) (in CH(2)Cl(2)). Using LDI-TOF mass spectrometry, the mono-phosphine complexes can be detected but not the bis-phosphine complexes. The electronic spectrum of 4 is similar to those previously reported with other tertiary phosphine ligands, whereas (DPAP)(I)Rh(TPP) (6) displays a low energy B-band absorption and a high energy Q-band absorption. In contrast to earlier reports, displacement of the methylide on rhodium in 5 could not be observed at any concentration, and the electronic spectra of 4 and 5 are almost identical. Isothermal titration calorimetry experiments showed that all binding events are exothermic, and all are enthalpy driven. The largest values of DeltaG degrees are found for 6. The thermodynamic and UV-vis data reveal that the methylide and the phosphine ligand have an almost identical electronic trans-influence on the sixth ligand.