Synthesis And Optical Properties Of V-Tipe Fluorene Derivatives

Fluorene derivatives are organic fluorescent materials with excellent optoelectronic properties and have wide applications in the fields of aggregation-induced emission and organic nonlinear optical materials.In this study,three V-type fluorene derivatives with D-π-A structures,BFPFO,DTFO and BFPDTS,were designed and synthesized based on a fluorene derivative（DPFO）with second-order nonlinear optical properties,and their structures were verified by ¹H-NMR,¹³C-NMR,HRMS and FTIR.On this basis,the preparation of crystals was carried out to investigate the effect of different solvents on the morphology of the aggregated states of the compounds,and the effect of intermolecular forces on the aggregation of DTFO was analyzed.The effect of solvent environment on the linear optical properties was explored in focus,and its second-order nonlinear polarizability（μ_gβ）of the molecule was calculated by solvatochromic method,and its second-order nonlinear optical properties were initially explored.The results show that.（1）Strip-shaped and Shuttle-shaped crystals can be formed by natural volatilization of saturated dioxane solutions of BFPFO and DTFO,respectively,and rhombic crystals can be formed by natural volatilization of saturated THF solutions of BFPDTS.The DTFO single crystals obtained by liquid-phase diffusion belong to the monoclinic system of P2₁/c.Four adjacent molecules are arranged in a centrosymmetric manner through C-H???πinteractions and C=O???H hydrogen bonding,and aggregate to form single crystals.（2）DPFO,BFPFO,DTFO and BFPDTS have obvious Aggregation-induced Emission（AIE）effects.In the dichloromethane/heptane solvent mixture,the compounds gradually aggregated with the increase of heptane content,and DPFO,BFPFO,and DTFO all formed H-aggregation and UV-VIS spectra were blue-shifted;BFPDTS formed J-aggregation and UV-VIS spectra was red-shifted;and The fluorescence emission spectra（PL spectra）of DPFO,BFPFO,DTFO and BFPDTS were all blue-shifted,and the fluorescence intensity of their aggregated states reached 4.97,3.95,5.01 and 3.27 times of the fluorescence intensity of the initial solution state,respectively.（3）Among the solvents with different polarities,the UV-VIS spectra of DPFO and BFPFO were mainly affected by the polar/dipolar effects of the solvents;the UV-VIS spectra of BFPFO and BFPDTS were mainly affected by the Hydrogen Bond Donor（HBD）and polar/dipolar effects of the solvents;the PL spectra of DPFO,BFPFO and DTFO were mainly influenced by the Hydrogen Bond Donor and Hydrogen Bond Acceptor（HBD and HBA）of the solvent;the PL spectra of BFPDTS were mainly influenced by the polarity/dipole effect of the solvent.（4）BFPFO,DTFO and BFPDTS all have typical Intramolecular Charge Transfer（ICT）characteristics,thus enhancing theirμ_gβ.Theoretical calculations show that BFPFO,DTFO and BFPDTS molecules have stronger second-order nonlinear optical properties than DPFO molecules.Among them,theμ_gβvalues of BFPFO and DTFO are enhanced by 20%and25%,respectively,compared with DPFO.theμ_gβvalue of BFPDTS reaches 9.28 times that of DPFO.Moreover,BFPFO,DTFO and BFPDTS molecules have good optical transparency,which solves the long-standing"nonlinear-transmittance"contradiction of nonlinear optical materials.This study provides new ideas and methods for the design and synthesis of functional organic optical materials with both AIE effects and second-order nonlinear optical properties.It is beneficial to advance the research process of organic small molecule materials applied in the field of biological detection and optical information transmission,and has potential applications in cell imaging,telecommunication and data processing,etc.