Theoretical Study On Two-photon Absorption Properties Of Tetraphenylethene Derivatives

Organic molecular materials with strong two-photon absorption properties have great potential applications in many fields,such as 3D optical information storage,photodynamic therapy,two-photon fluorescence microscopy(TPEM),and so on.In particular,the TPEM imaging has received extensive attention in recent years because of its vital uses in the study of living cells and tissues.Therefore,exploring the potential applications of organic two-photon absorption materials has become a hot study point for researchers.However,under the restriction of the experimental materials,equipment,costs and other factors,the speed and efficiency of experimental study is not satisfactory.In recent years,using the quantum chemical calculation theory to explore the relationship between structure and two-photon absorption properties has become the focus of many researchers.Theoretical study can guide the synthesis of experimental molecules,thus greatly saving the time and cost of research.At present,a series of symmetric or asymmetric charge transfer molecules(such as D-?-D,D-?-A,D-A-D,etc.)with ? conjugation centers,electron donors(D)and receptors(A)have been extensively studied in both theory and experiment.The effects of various intra-molecular structural factors(such as molecular planarity,donor and acceptor intensity,electron properties of ? conjugated centers,etc.)and intermolecular interactions(such as aggregation effects and solvent effects)on the two-photon absorption properties are fully studied.Therefore,according to the existing relationships between the molecular structure and properties,it is possible to design two-photon absorption material theoretically.Based on the hybrid density functional theory,a series of organic molecular systems constructed from tetraphenylethene groups have been studied theoretically,and the relationship between the structure and properties was discussed.The main work of this paper can be divided into the following two parts: In the first part,westudied the effects of dimerization and isomerization on two-photon absorption properties of a class of tetraphenylethene derivatives.Based on these tetraphenylethene derivatives,in second part,the structures of a series of organic two-photon absorption molecules have been designed and the two-photon absorption properties of the designed molecules have been calculated.I.Dimerization and Isomerism Effects on Two-Photon Absorption of Tetraphenylethene DerivativesThe two-photon absorption properties of a novel tetraphenylethylene derivative ENPOMe molecule and its isomers were calculated theoretically.The dihedral angles between the benzene ring planes were collected for the considered four kinds of molecular structures.The results show that the molecular isomorphism has an important effect on the two-photon absorption properties,and the partial planarity of the molecules can enhance the two-photon absorption intensity.In order to explore the aggregation effect,12 kinds of covalently linked dimers were designed and their two-photon absorption properties were calculated.It is found that the linear arrangement of branches can effectively enhance the two-photon absorption properties.The two-photon absorption properties of the molecule are similar because the structure with similar angles between the branches and the backbone has similar intra-molecular conjugate channels and charge transfer capacity.Partial planarity and linear arrangement are the possible reason for the observed aggregation-induced two-photon absorption enhancement.II.Molecular Design for Two-Photon Absorption Materials based on Tetraphenylethene DerivativesOn the basis of the experimental molecules,we have designed a series of tetraphenylethene derivatives which is helpful to enhance the two-photon absorption cross section after taking the existing structure and property relationships into account.By changing the electron donor groups in the molecule and enhancing the strength of the donor,we designed two kinds of molecular structures,and found the corresponding two-photon absorption intensity of the designed molecules are stronger than that of the experimental molecule.At the same time,it has also been found thatchange of the connection mode of the carbazole group can improve the two-photon absorption intensity.Also,3 dimers have been designed under the consideration of related experimental results.In comparison with the dimer structure of the experimental molecule,the designed dimer structures with ethylene and acetylene conjugated bridges can enhance the two-photon absorption greatly in the longer wave range.The calculation results confirmed our design strategy.Our designed molecules not only have strong two-photon absorption,but also have the aggregation-induced emission properties because the molecules contain the tetraphenylethene group with the propeller structure.Therefore,they could be excellent candidates for two-photon fluorescent probes.This research is helpful for the design of efficient two-photon absorption materials.