| Until now,organic near-infrared fluorescent materials have achieved tremendous development and been widely used in fields such as optical information communication,biological tissue and cell imaging,two-photon fluorescence probes,various ion detection and sensors,and electroluminescent devices.Donor-Acceptor(D-A)molecules can be more conducive to designing and synthesizing NIR fluorescent materials because it can randomly select groups with different capacities donating and withdrawing electron,and the conjugate length can be adjusted.D-A molecules have obvious intermolecular interactions and a large degree of conjugation.In this case,a large two-photon absorption cross section can be obtained.But few studies on nearinfrared luminescent materials were made relativly because they often exhibit aggregation caused quenching with low fluorescence quantum efficiency.Therefore,attaching the advantages of AIE to the molecular design and synthesis of near-infrared fluorescence with excellent performance has become the point of our research.In this paper,aromatic heterocyclic rings were selected as acceptors and space-twisted D-A-D type NIR fluorescent molecules were designed and synthesized to explore the relationship between structures and properties.1.We designed and synthesized new fluorescent molecules TQ-BPCZ and TQBP2 PA by using [1,2,5]thiadiazole[3,4-g]quinoxaline(TQ)as an electron acceptor group,carbazole and triphenylamine as electron donor groups respectively.We zeroed in on the influence of different structural donors on the photophysical properties of the molecule in solution and aggregation states.It was found that TQ-BP2 PA behaves aggregation-induced emission with emitting weak fluorescence in THF and strong fluorescence in aggregation state.The solid state fluorescence quantum efficiency is 8 times that of the solution state.At the same time,the aggregation-induced luminescence property promoted the two-photon absorption cross-section of TQ-BP2 PA from 316 GM in the THF solution to 7283 GM in the nanodispersion(water fraction is 90%).TQ-BP2 PA was proved to be the fluorescent material with excellent two-photon absorption properties.In contrast,with the addition of poor solvent water,TQ-BPCZ exhibits weak aggregation caused quenching,but still maintains a high luminous intensity in a variety of pure solvents.And the strong spatially distorted conformation suppresses the ?-? stacking,making the quantum efficiency of solid state reach 34.34%.The photoluminescence emission peaks of TQ-BPCZ and TQBP2 PA are at 712 nm and 683 nm respectively,indicating that they are a kind of near infrared fluorescent material.Bonded long alkoxy chains make the better solubility of the two molecules,and are favorably applied to solution processing type red light devices.2.We continued constructing the other D-A molecule which was diffreret from two before.We synthesized molecule DBTP,taking diphenyl[a,c][1,2,5]thiadiazolo-[3,4-i]phenazine(DTP)as the acceptor with a more conjugated plane and triphenylamine as the donor,while reducing the distance between the electron donor and the acceptor.Electrochemical and frontier orbital theory calculations found that the more absorbing groups and reducing the conjugate length between D and A,DBTP would has stronger intramolecular charge transfer.The maximum solid PL emission peak ? is 737 nm.The free rotation of the peripheral groups is limited so that the molecules have good AIE properties.When the water content is 95%,there was a certain luminous intensity.The fluorescence quantum efficiency increased from 0.8% of the THF solution to 13.2%.The benzene ring with an alkoxy chain still make it more solvable.The AIE property of DBTP made its two-photon absorption cross section up to 5500 GM,which proved that the AIE property could improve the two-photon absorption.This phenomenon is universal.Single-photon stimulating biological cell imaging demonstrated the low toxicity of DBTP,indicating its promising application in two-photon bioimaging. |
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