Sign Response Mechanism of TCA Self-assembled Fluorescence Probe for Cu2+ Detection:RET Evidence by DFT①

LI Fu-Jun SA Rong-Jin

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Sign Response Mechanism of TCA Self-assembled Fluorescence Probe for Cu2+Detection:RET Evidence by DFT①

LI Fu-Juna②SA Rong-Jianb

a(()110044)b(350002)

A new type of self-assembled molecule ON-OFF fluorescence probe for toxic transition metal ions, made up of thiacalix[4]arene, micelle and fluorescence group,has been studied by DFT/TDDFT method combined with experiment spectra. Since the mechanism of the optical quenching signal response of such self-assembled micelle probe has always been a controversial issue of uncertainty, the spatial construction and geometric structures of the functional unitsof probe in the Cu2+ion detecting process were calculated and the mechanism was investigated bythe molecular transition orbital pairs method to explore the origination of ON-OFF fluorescence sign response. The results presented that the signal response mechanism of the micelle probe is ascribed to F?rster resonance energy transfer(FRET) which provides new sights different from most of the conclusions by the related research workreported.

ON-OFF fluorescence probe, density functional theory, F?ster resonance energy transfer, heavy metal ions detection, micelle self-assembled complex;

1 INTRODUCTION

Copperis an essentialelement for human life which plays an important role in fundamental physiological processes in human body. Meanwhile, like any other heavy metal elements, it is potentially toxic under certain concentrations. Under this consideration, many kinds of Cu2+-selective fluore- scent chemosensors to measure the amount of Cu2+ion in the sources contaminated with copper ion including human body have been developed[1,2]. For the detecting of Cu2+ion, the recognition site of sensors is usually metal-chelating molecule designed to bind the target ion selectively and the readout system is very often a fluorophore. The two com- ponents of the sensors are usually covalently bound through a spacer and a variation of the position and/or intensity of the emission spectrum of the fluorophore would happen as the result of the chelating of the metal ion[3, 4]. For the fluorescence probes of ON-OFF type[5-8], the binding of Cu2+ion results in a quenching of the fluorescence emission of the probe and allows its detection in the micro- or submicromolar range. In most of these systems the quenching is ascribed to a photoinduced metal-to-fluorophore electron-transfer mechanism[6]. How- ever, there are still sensors reported in which the binding of a Cu2+ion causes an increase in the fluorescence emission by the groups of Bharadwaj[9]or in which the fluorophore and the metal ion do not interact directly by Tonellato[10)and Arnold[11], which cannot all be reasonably explained by elec- tron-transfer mechanism. Self-assembling ON-OFF fluorescence chemosensors belong to the latter situation, and the general advantages of this type include the solubility in water, the easy design, realization, and testing of new effective sensing systems. Although there are considerably fewer reports compared with conventional chemosensors, the self-assembled heavy metal ion probes have been reported for a decade[6-8], however, there is rare research report on the mechanism of the signal response, even rare on the related theoretical work. Fernandez and coworkers[12]reported an ON-OFF sensor of self-assembling set-up for Ni2+and Cu2+in water. For the signal response mechanism, they merely demonstrated that the energy-transfer or electron-transfer is responsible for the fluorescence quenching signal. Iki ascribed the mechanism of self-assembled TCA/TCAS probes for metal ions detection to energy-transfer[13]. Kimsystema- tically expounded the mechanisms which control the response of calixarene-derived fluorescent probes including Photo-induced electron transfer(PET), fluorescence(F?rster)resonance energy transfer(FRET), excimer/exciplex formation or extinction and photoinduced charge transfer(PCT)[14].As the recognition part of a chemosensor, thiacalix[4]arene derives are relatively large molecules and more applicable to self-assembling fluorescence chemo- sensors than to the other types, with the unique and superior features of ability of forming specific complex with soft metal ions[15,16]and easy modi- fication at the lower rim with various cation-ligating groups for improving metal-binding ability, such as amides, esters and crown ethers[16]. In recent years, a kind of self-assembled TCA/micelle chemosensor for Cu2+ions has been studied and prepared, realizing a system in which the active components assemble spontaneously, without any covalent link between them[17]. In this paper we study the mechanism of TCA/micelle self-assemble fluorescence probe of ON-OFF signal for Cu2+detection by DFT/TDDFT method. The results analysis based on orbital pair’s analysis considering the experimental data suggests that the mechanism is identical to the FRET process.

2 COMPUTATIONAL METHODOLOGY

The selection of theoretical methods and com- putational models has to meet the requirements of both accuracy and computing economy.

Density functional theory (DFT) has been widely used in most branches of chemistry, optical che- mistry, biochemistry, and materials[18,19]. By DFT, all of the molecular properties are solely determined by the electron density, and is generally evaluated by solving the Kohn-Sham equation which includes kinetic, Coulombic, exchange, and correlation terms. The choice of the XC functional is directly corre- lated to the quality of DFT results. Although the exact functional of DFT is still unknown, various alternative methods[20,21], together with various empirical corrections such as dispersion, have been successfully implemented in many popular computational codes.

B3LYP, a hybrid of exact Hartree-Fock exchange with local and semi-local exchange and correlation terms on the basis of the adiabatic connection[22-24], represents the most famous global hybrid GGA and has been used extensively in nearly all domains of chemistry. Without any optimization, B3LYP functional performs fairly well in the calculations of structures and energies of organic and inorganic compounds and chemical reactions. B3LYP as the most popular DFT method has dominated the DFT market for nearly 20 years. There are some litera- tures which have reported the incorrect long range charge transfer behaviors between donor and acceptor. The DFT-derived result sometimes esti- mates some properties of donor--conjugated bri- dge-acceptor (D--A) systems[25,26]inaccurately, even in large error. To overcome this problem, some long-rang-corrected functionals have been develo- ped recently, such as CAM-B3LYP[27], BHandHLYP[28], LC-BLYP[29],In this paper, the geometric and electronic structures of the Cu2+–TCA complex and the fluorophore capsuled in micelle, containing D--A systems, were studied, and the signal response mechanism was analyzed based on the Uv-vis spectrum calculation and the response process was simulated. The quality of our results mostly depends on the accuracy of the adiabatic calculations including hydrogen bonds and vertical excitation of the states including long range charge transfer. CAM-B3LYP is a comparatively credible and efficient method to deal with the situation[25], and was chosen to take the whole calculation work.

All the calculations were performed with the Amsterdam Density Functional (ADF2012) pro- gram[30]. As the complexes are relatively large molecules with transition metal ions, the relativistic effects and electron correlation were taken into account. The zero-order regular approximation (ZORA)[31]was adopted for each atom to account for the scalar relativistic effects. The frozen-core approximation was adopted on all the elements: The core orbitals of the non-metal elements O and S were frozen up to 1and 2respectively, while those of Cu frozen up to 3. A standard valence triple-STO basis set with valence polarization functions (TZVP)[32]was used. For the discussion of signal response mechanism of the NLO response, the vertical excitation energy was calculated by time dependent DFT (TDDFT) methods, and the UV-Vis absorption spectra were plotted with the Gaussian peak-shape modification by a width at the half-height of 3000 cm-1.

As the Cu2+detection is in the solution environ-ment, the solvent effect was taken into account and the PCM[33-36]model is applied at all of the calcula- tions for polar solvent water.

3 RESULTS AND DISCUSSION

3. 1 FRET process and the initiating conditions

In a FRET process, what in good agreement with the character of TCA self-assembled complex are that there is no electron transfer involved in and no constant connections like bonds between the donor part (usually fluorescence molecules in excited states) and the acceptor part (usually recognition molecules chelating metal ions) forming. The acceptor absorbs the energy of the donor in high level by instantaneous collisions, and then the donor lost energy comes back to its ground state. Mean- while, the acceptor will be excited to higher energy levels, and then release the energy by emitting fluorescence in different colors or nonradiative jump to come back to its ground state. Thereby, the optic phenomenon produced and can be used for ions detection. The triggering of FRET need three essential factors as empirical rules: (1) the emission spectrum of the donor overlaps the absorption spec- trum of the acceptor effectively (generally, greater than thirty percent); (2) the fluorescence chromo- phores of the donor and acceptor arrange in an appro- priate manner (transition dipole moments match each other); (3) the distance of the donor and accep- tor is between 7～10 nm. In addition, many other fac- tors, such as quantum yield, extinction coef- ficient, water-solubility and capacity of resisting disturbance, can also affect the FRET procedure formation.

3. 2 FRET clues in experiment

In recent years, we have synthesized a new type of amphipathic self-assembled TCA/micelle com- plex and use it for heavy metal ions detection in water. The analytical experiment illustrated that with the perylene molecules as fluorescence group, the complex could detect copper ions with high sensi- tivity and selectivity by ON-OFF optical phenomena produced, even with the coexistence of usual pollu- ting metal ions such as Ni, Zn, Pb and Cd. The Uv- vis spectrum analysis showed that there really are overlap areas in the absorption spectrum of TCA complex coordinated by Cu2+ions and the emission spectrum of perylene, which is the first clue sugges- ting the possibility of FRET process. The structure analysis experiment told that as the copper ions add and the ON-OFF phenomena produce, there is no new bonds between the perylene molecules and the TCA complexes forming, but only new (O)–Cu2+bonds between TCA molecules and Cu2+ions appeared, which is the second clue suggesting the FRET process.

3. 3 FRET evidence in DFT calculations

3. 3. 1 Geometry structure

Fig.1 showsthe conceptual graph of the cup structure of thiacalix[4]arene chelating with Cu2+in ball-and-stick representation with the atom symbols. Thiacalix[4]arene is composed of four benzene rings, linked to each other via sulfide bridges, through which, unlike the conventional calix[4]arene, it can form specific complex with soft metal ions[15,16]. As shown in Fig. 1, when the H atoms of -OH group of the TCA cup bottom were ionized in different extents under the influence of pH value, Cu2+would get close to the bottom and chelate with –O–and –S– in different manners and then form three center two electron 3e-2c bond and/or triple bridge bond of metal center3-M. For the sake of discussion con- venience, we take the TCA complexes chelating different numbers of Cu2+as TCA + 1Cu2+, TCA + 2Cu2+, TCA + 3Cu2+and TCA + 4Cu2+, respectively.

Fig. 1. Structure of thiacalix[4]arene chelating with Cu2+ions

Table 1 lists the representative optimized parame- ters of the geometric structures along with the experi- mental measured data of the complex Thiaca- lix[4]arene, andFig. 2 shows the labeling scheme of the structures with TCA chelating fours Cu2+ ions as representation. The optimized geometric parameters are all in reasonable agreement with the experimental data.The molecular energies are also listed in Table 1. The energies of the four complexes are low enough to confirm the stability and realizability of these simulated structures by DFT calculation. The lowing trend of the energy as the increasing number of Cu2+ ions chelated by TCA suggests the increase of the stability of the structures.

aThe parameters of the structure from experimental data[37].bThe inner-cup angles between the two planes by the benzene rings (B1, B3).cThe inner-cup angles between the two planes by the benzene rings (B2, B4).

Fig. 2. Labeling scheme of the geometric structure of TCA chelated by 4 Cu2+ ions

Here in the self-assembled TCA complexes system, the chelating of Cu2+ions is certain to change the spectra properties of TCA complexes. Meanwhile, by self-assembled procedure, the hydro- phobic end groups (butyl groups) of the amphipathic TCA rely on together forming cavity in water and the perylene molecules are packaged in, providing effective collision distance between perylene molecules and TCA complexes, and creating conditions for the origination of FRET processes.

Fig. 3. Optimized geometric structures of TCA chelated by 1 Cu2+ion (a), 2 Cu2+ions (b), 3 Cu2+ions (c) and 4 Cu2+ions (d), respectively. M = Cu2+, B = tert-butyl benzene

3. 3. 2 FRETsignal response and spectrum analysis

Fig. 4 shows the UV-Vis spectra of the fourTCA complex structures with different chelating Cu2+ion numbers from 1 to 4, and the fluorescence spectrum of perylene from experiment data. It is shown that as the Cu2+ions chelated increase, the absorption peaks of TCA complexes red shift and the overlap areas with the fluorescence spectrum of perylene are increased.

Fig. 4. Fluorescence spectrum of perylene from experiment, and the absorption spectra of TCA complexes chelating different numbers of Cu2+ions

Table 2 lists the overlap areas ratio of the four donor-acceptor pairs (D/A pairs), corresponding to the F?rster distanceR(the distance between the D/A pairs when the energy transfer efficiency equals 50%).Rwas calculated (in angstroms) using the spectroscopic properties of the probes (Van Der Meer et al., 1994)[38]:

whereQis the quantum yield of the donor (taken as 0.12):2is the orientation factor (taken as 2/3);is the refractive index of the medium between the probes (taken as 1.333);Jis the normalized spectral overlap integral (M-1×cm-1×nm4). The overlap integral was calculated as:

Table 2. Overlap Areas Ratio of the Four D/A Pairs and the F?rster Distance

As shown in Table 2, the increase number of Cu2+ions chelated by TCA makes the overlap areas of the absorption spectra of the donor, TCA+Cu2+com- plexes, with the emission spectrum of the acceptor, perylene molecule, increasing from 23.3% to 84.4%. Meanwhile, the F?rster distance is also increased from 13 to 17 ?. According to formula (3), the curves that the FRET efficiency. the distance changes between the A/D pairs were plotted, see Fig. 5. It is shown that more Cu2+ions chelated, the energy transfer efficiency falling slower as the distanceincreases. For TCA+4Cu2+complex, as the fluorescence group perylene gets closer, whenis shortened to 4 nm, the FRET process would have a possibility to occur, and the distanceis 3.2, 2.8 and 2.5nm, respectively for TCA+3Cu2+, TCA+2Cu2+, and TCA+1Cu2+to get the possibility of starting the FRET process.

Fig. 5. FRET efficiency corresponding to the D/A pairs distance

3. 3. 3 FRET procedure and the orbital pairs analysis

The structure of TCA, as the donor of D/A pairs in the FRET processes, is in relatively complex composition, and the transition dipole moments are multiple directional oriented when excited. To intrigue FRET response, when TCA is attacked and coordinated by Cu ions, the space arrangement of TCA and the fluorescence group perylene need to meet the coupling requirements of the transition dipole moments which contribute the most to the absorption spectrum.

The molecular orbital pairs theory has been used to analyze the nonlinear optical (NLO) response of NLO molecules[39,40], which can relate the NLO response to the molecular orbital transition pairs directly, thereby further linking the NLO property to the concrete molecular structure. Here we carry over the theory, for giving a direct expression of the FRET efficiency on the molecular structures. The contribution of orbital transition pairs to the FRET efficiency was calculated by formula (4) and (5) as follows:

whereis the transition coefficient of theth orbital pair of theth excited state, and f is the absorption strength of the overlap area of theth excited state. The transition orbital pairs contributing the most to the energy transfer are shown in the Fig. 6～9, with their contribution ratios also listed.

For the complex TCA+1Cu2+, the transition orbital pairs contributing to the FRET process were 61 pairs in all, and as shown in Fig. 6, the main tran- sition orbital pairs making most of the contribution (> 50%) were 5 pairs, mainly from the occupied orbitals made up of the delocalizedorbital of benzene ring, to the lowest unoccupied molecular orbital (LUMO), mainly made up of the delocalizedorbital of benzene ring. The orbitals of Cu2+ion were nearly not involved in, although the com- plexing of Cu2+made the Uv-vis spectrum of the TCA complex red shifted and overlapped effectively with the fluorescence spectrum of perylene, as shown in Fig. 4.

Fig. 6. Transition orbital pairs contributing the most to the FRET process of TCA+1Cu2+

The transition orbital pairs of TCA+2Cu2+com- plex made contribution to the FRET process were 91 pairs in all, and the main pairs made most of the contribution (>50%) see Fig. 7, were 10 pairs, which were also concentrated on from the delocalizedorbitals of the benzene rings and the tert-butyl groups to the delocalizedorbitals of the benzene ring. The differences from that of TCA+1Cu2+complex, were that with one more Cu2+coordinated, more orbital pairs transition would be engaged in the contribution to the FRET process, and the contri- buting proportion of single orbital pair was reduced, meanwhile, the orbitals of Cu2+were still not involved suggesting that the effect of the Cu2+are still indirect.

Fig. 7. Transition orbital pairs contributing the most to the FRET process of TCA+2Cu2+

As for the complex TCA+3Cu2+, the orbital pairs engaged in the contribution increased to 141 pairs, compared with the two less Cu2+ions chelating TCA complexes, and the main pairs contributing the most (> 50%) were 17 pairs. See Fig. 8, the main orbital pairs transition was mainly from theandorbitals of tert-butyl groups to the delocalizedorbitals of the benzene ring. Specially, the delocalizedorbitals of benzene ring are much less in the donor part of the pairs compared with the two less chelated TCA complexes. In addition, it is worth noting that the highest occupied molecular orbital (HOMO) also participated in the acceptor parts of the main pairs, which Is a reasonable result theoretically based on the characteristic of the extra-nuclear electron configuration of Cu2+ions that there is a single electron in the outermost orbital, and means that the HOMO orbital is half full and can accept another excited electron, thus giving further expression to the dominant function of Cu2+in the FRET pro- cesses.

Fig. 8. Transition orbital pairs contributing the most to the FRET process of TCA+3Cu2+

With the most Cu2+ions chelating, compared with the other three molecule structures, the TCA+4Cu2+complex embodied the lowest energy absorption in the excitation spectrum and the largestJvalue, which should suggest the great possibility of FRET processes. The transition orbital pair analysis told that 183 pairs would be engaged in contributing to the FRET processes (increased 42 pairs compared with that of TCA+3Cu2+), and most contributions were to the 35 pairs (> 50%), and the top 21 pairs (the total contribution was 32%) among them are shown in Fig. 9. For displaying our analysis result as clear as possible, the orbital components and the contribution ratio of every orbital of the 21 pairs are listed in Table 3.

Fig. 9. Transition orbital pairs contributing the most to the FRET process of TCA+4Cu2+

Table 3. Orbital Components of the Transition Orbital Pairs Contributing to FRET Sign Response for TCA + 4Cu2+ Complex

Since the structure TCA+4Cu2+complex was in4vsymmetry, the orbital pairs were all symmetric. The transition was mainly fromorbitals of tert-butyl groups to the delocalizedorbital of benzene rings andorbital of tert-butyl groups, and theorbital of Cu2+and* orbital of C–S–C bond also took a little part in the donor pairs. Specially, here the acceptors of the pairs were all made up of the four highest occupied orbitals with vacancies. The single electron structure of the Cu2+outermost orbital, which lowed the transition energy, was responsible for the red shift of the absorption spectrum.

In conclusion, with the increase of chelated Cu2+ions, from TCA+1Cu2+to TCA+4Cu2+, the number of the molecular orbital pairs engaged in contri- buting to the FRET processes was increasing, and the transition energy was reducing, and the com- position of the donors orbital was changing from the orbital of benzene rings and tert-butyl groups together to that of the tert-butyl group mainly. The transition energy lowering led to the red shift of the absorption spectra, which would not only make the transition much easier, but of particular importance, make the overlap area with the fluorescence spec- trum of perylene increase. The orbital composition change of the donor to the orbital of tert-butyl groups mainly also suggests a greater liability of FRET effect because of a higher chance of impact contact with the fluorescence group, as the TCA cup rim is made up of tert-butyl groups. The analysis result of the increasing liability of FRET effect from TCA+1Cu2+to TCA+4Cu2+is in good agreement with the ON-OFF experimental phenomena that the addition of Cu2+ions weakens the fluorescence emission, and when adding more Cu2+anions, the weakening is further till the quenching of the fluorescence sign.

3. 3. 4 Spatial arrangement of the functional units of the FRET fluorescence probe

In the experiment work of the TCA self-assem- bled fluorescence probe for Cu2+detection[18], we have exhibited that, in the water environment with the pH value exceeding 7, the addition of Cu2+ions leads to the reducing of the fluorescence peak of perylene molecules in the existence of TCA molecules. As more Cu2+is added, the reducing is further till the quenching of the fluorescence sign, and the Uv-vis spectrum analysis verifies the exis- tence of the complexes of TCA chelating Cu2+and the existence of perylene molecules without che- mical change. Thus, it is identified that the probe for Cu2+detection made up of TCA and perylene in alkaline water environment is self-assembled based on the amphipathy of TCA, and the mechanism of quenching sign response is generally speculated to be energy or electron transfer. There are no new bonds between TCA molecule and the fluorescence group perylene. It is in low probability to be electron transfer mechanism. Here we present reasonable explanation for the energy transfer mechanism by spectrum analysis and orbital pair analysis. Firstly, within limits, the more Cu2+ions addition, the higher overlap integral in the absorption and emission spectra of TCA complexes and perylene molecules, precisely corresponding to the experimental phenol- mena that more copper sulfate addition, more of the fluorescence radiation weakening until quenching; secondly, as the FRET effect deepens from the complex TCA+1Cu2+to TCA+4Cu2+, the change of the main composition from the orbital of benzene ring to the orbital of tert-butyl group of the donor of the main orbital pairs precisely corresponds to the rising higher symmetry of the TCA complex structure and the amphipathy of TCA to form cavity in water to package small organic molecules like perylene molecules. Thus, the space arrangement of the functional units of the self-assembled fluore- scence probe in the FRET processes should be as shown in Fig. 10: the perylene molecules are caged in the cavities formed by the amphipathic TCA molecules in water, and the diameters of the cavities should in the ranges of 2～5.75 nm, 2～6.35 nm, 2～7.15 nm and 2～8.35 nm for complexes TCA+1Cu2+, TCA+2Cu2+, TCA+3Cu2+, and TCA+1Cu2+respectively to insure the FRET sign response occurrence.

Fig. 10. Relative positions of the groups of the self assembled fluorescence probe in FRET process

4 CONCLUSTION

In this work, we applied high-level DFT methods to study the self-assembled TCA complexes fluorescence probe of a new ON-OFF type for the detection of Cu2+ions. The geometric structures of the four complexes, TCA+1Cu2+, TCA+1Cu2+, TCA+3Cu2+, and TCA+1Cu2+, were theoretically simulated andoptimized. The results of the study on the thermo stability suggest that the simulated structures are stable and realizable. The spectra analysis and molecular orbital pairanalysis were used to study the quenching sign mechanism of the probe, and the results told that the F?ster resonance energy transfer explains the experimental phenol- mena impeccably, and the spatial construction of the functional units of the self-assembled fluorescence probe was deduced base on the FRET theory and exhibited. Here it is the first time that the orbital pairs analysis method was used for the sign response mechanism of the molecular fluorescence probe, as it is used to analyze the NLO response. Also, it is the first time that the type of self-assembled fluore- scence probes is analyzed and explained clearly by FRET theory.

(1) Chang, H. Q.; Zhao, X. L.; Wu,W. N.; Jia,L.; Wang, Y. A highly sensitive on-off fluorescent chemosensor for Cu2+based on coumarin.. 2017,182, 268-273.

(2) Mahapatra,A. K.; Mondal,S.; Manna, S. K.; Maiti,K.; Maji, R.; Uddin,M. R.; Mandal,S.; Sarkar,D.; Mondal, T. K.; Maiti, D. K. A new selective chromogenic and turn-on fluorogenic probe for copper(II) in solution and vero cells: recognition of sulphide by [CuL].2015,6490-6501.

(3) Alreja,P.; Kaur, N.Recent advances in 1,10-phenanthroline ligands for chemosensing of cations and anions.2016,23169-23217.

(4) Giri, D.; Patra,S. K. Benzodithieno-imidazole based-conjugated fluorescent polymer probe for selective sensing of Cu2+.2015,79011-79021.

(5) Wang, Y.; Chang, H. Q.; Wu, W. N.; Mao, X. J.; Zhao, X. L.; Yang, Y.; Xu, Z. Q.; Xu, Z. H.; Jia,L. A highly sensitive and selective colorimetric and off-on fluorescent chemosensor for Cu2+based on rhodamine 6G hydrazide bearing thiosemicarbazide moiety.2017,335, 10-16.

(6) Santis, G. D.; Fabbrizzi, L.; Lichelli, M.; Mangano, C.; Sacchi, D.; Sardone, N.A fluorescent chemosensor for the copper(II) ion.1997, 257, 69-76.

(7) Yoon,J.; Ohler,N. E.; Vance,D. H.; Aumiller,W. D.; Czarnik, A. W. A fluorescent chemosensor signalling only Hg(II) and Cu(II) in water.1997, 38, 3845-3848.

(8) Torrado,A.; Walkup,G. K.; Imperiali,B.Exploiting polypeptide motifs for the design of selective Cu(II) ion chemosensors.1998, 120, 609-610.

(9) Ghosh,P.; Bharadwaj,P. K.; Mandal,S.; Ghosh,S.Ni(II), Cu(II), and Zn(II) cryptate-enhanced fluorescence of a trianthrylcryptand:? a potential molecular photonic or operator.1996, 118, 1553-1554.

(10) Grandini,P.; Mancin,F.; Tecilla, P.; Scrimin,P. P.; Tonellato,U. Exploiting the self-assembly strategy for the design of selective CuIIion chemosensors.1999, 38, 3061-3064.

(11) Sasaki,D. Y.; Shnek,D. R.; Pack,D. W.; Arnold,F. H. Metall-induzierte dispersion von lipid-aggregaten; ein einfacher, selektiver und empfindlicher fluoreszenzsensor für metall-ionen.1995,107, 994-996.

(12) Fernandez,Y. D.; Gramatges,A. P.; Amendola,V.; Foti,F.; Mangano,C.; Pallavicini, P.; Patroni, P. S. Using micelles for a new approach to fluorescent sensors for metal cations.2004,1650-1651.

(13) Iki,N. Non-covalent strategy for activating separation and detection functionality by use of the multifunctional host molecule thiacalixarene.. 2009,64, 1-13.

(14) Kim,J.S.; Quang,D.T. Calixarene-derived fluorescent probes.2007,107, 3780-3799.

(15) Kumagai,H.; Hasegawa,M.; Miyanari,S.; Sugawa,Y.; Sato, Y.;Hori,T. Facile synthesis of-tert-butylthiacalix[4]arene by the reaction of p-tert-butylphenol with elemental sulfur in the presence of a base.1997, 38, 3971-3972.

(16) Morohashi,N.; Narumi,F.; Iki,N.; Hattori,T.; Miyano,S. Thiacalixarenes.2006,106, 5291-5316.

(17) Hu,X. J.; Li,C. M.; Song,X. Y.; Zhang, D.; Li, Y.S. A new Cu2+-selective self-assembled fluorescent chemosensor based on thiacalix[4]arene.. 2011,14, 1632-1635.

(18) Kohn,W.; Becke,A.D.; Parr,R.G. Density functional theory of electronic structure.1996, 100, 12974-12980.

(19) Burke,K.Perspective on density functional theory.2012,136, 150901-150910.

(20) Sousa,S.F.; Fernandes,P.A.; Ramos,M.J. General performance of density functionals.2007,111, 10439-10452.

(21) Korth,M.; Grimme,S. “Mindless” DFT benchmarking.2009, 5, 993-1003.

(22) Harris,J. Adiabatic-connection approach to Kohn-Sham theory.1984, 29, 1648-1659.

(23) Stephens,P.J.; Devlin, F.J.; Chabalowski,C.F.; Frisch, M.J.calculation of vibrational absorption and circular dichroism spectra using density functional force fields.. 1994, 98, 11623-11627.

(24) Becke,A.D. Density-functional thermochemistry. III. The role of exact exchange.1993, 98, 5648-5652.

(25) Zhang, L.H.; Wang, Y.; Ma,F.; Liu, C. G. Theoretical studies on photo-triggered second-order nonlinear optical switches in a series of polyoxometalate-spiropyran compounds.2012,716, 245-251.

(26) Lu,L. L.; Hua,H.; Hou,H.; Wang,B. S. An improved B3LYP method in the calculation of organic thermochemistry and reactivity.2013, 1015, 64-71.

(27) Yanai,T.; Tew,D.; Handy,N. A new hybrid exchange-correlation functional using the Coulomb-attenuating method (CAM-B3LYP).2004, 393, 51-57.

(28) Becke,A. D. A new mixing of Hartree-Fock and local density-functional theories1993, 98, 1372-1377.

(29) Iikura, H.;Tsuneda, T.;Yanai,T.; Hirao,K.A new mixing of Hartree-Fock and local density-functional theories.2001, 115, 3540-3544.

(30) Guerra,F.; Visser,O.; Snijders,J. G.; Velde,G. T.; Baerends, E. J.; Clementi,E.; Corongiu, C.STEF, Calgary1995,303-395.

(31) Lenthe,E. V.; Baerends,E. J.; Snijders,J. G. Relativistic regular two-component Hamiltonians.1993, 99, 4597-4610.

(32) Schaefer, A.; Huber, C.; Ahlrichs, R. Fully optimized contracted Gaussian basis sets of triple zeta valence quality for atoms Li to Kr.1994, 100, 5829-5835.

(33) Miertu?,S.;Scrocco,E.; Tomasi, J. Electrostatic interaction of a solute with a continuum. A direct utilization ofmolecular potentials for the prevision of solvent effects.1981,55, 117-129.

(34) Miertu?, S.; Tomasi,J. Approximate evaluations of the electrostatic free energy and internal energy changes in solution processes.1982, 65, 239-245.

(35) Pascual-Ahuir,J. L.; Silla,E.; Tu?ón, I. GEPOL: an improved description of molecular-surfaces. 3. A new algorithm for the computation of a solvent-excluding surface.1994,15, 1127-1138.

(36) Tomasi,J.; Mennucci,B.; Cammi, R. Quantum mechanical continuum solvation models.2005, 105, 2999-3093.

(37) Akdas,H.; Bringel,L.; Graf, E.;Hosseini, M. W.; Mislin, G.;Pansanel, J.;Cian, A. D.; Fischer,J. Thiacalixarenes: synthesis and structural analysis of thiacalix[4]arene and of p-tert-butylthiacalix[4]arene.1988, 39, 2311-2314.

(38) Meer, V. D.; Cooker,B. W.; Coker III,G.; Chen,S. Y.VCH Publishers, Inc., New York 1994, p150.

(39) Li,F. J.;Hu,X. J.; Sa,R. J. Receding mechanism of NLO response of polyanion [M8O26]4?(M = Cr, Mo, W) and the closed loops theory analysis.2014,38, 2619-2628.

(40) Hieringer, W.; Baerends, E. J. First hyperpolarizability of a sesquifulvalene transition metal complex by time-dependent density-functional theory.2006,110, 1014-1021.

25 October 2017;

22 May 2018

① This project was supported by the Natural Science Foundation of Liaoning Province (201602516), and Shenyang Project of Young and Middle-aged Innovative Talents of Science and Technology (RC170244)

.Li Fu-Jun, associate professor, engaged in theoretical studies on the environmental functional materials of little quantum dots. E-mail: bamboo_lfj@163.com

10.14102/j.cnki.0254-5861.2011-1867