Design,Synthesis And Application Of Photothermal Conversion Materials Based On Intermolecular Charge Transfer

Organic charge transfer materials are dual-or multi-component materials consisted by electron donor and electron acceptor through charge transfer interaction with a certain stoichiometric ratio.Due to its advantages of flexible structure design,solution processing and low cost,organic charge transfer materials play a crucial role in the design and preparation of functional materials.Different from single-component materials,organic charge transfer materials can not o nly maintain some properties of single-component molecules,but more importantly,effective charge transfer mechanism can also give materials some rare novel properties,such as white light emission,nonlinear optics,organic photovoltaic,stimulus respons e,photothermal conversion,etc.However,there are still some problems concerning the further development of organic charge transfer materials,including low degree of charge transfer,poor stability of charge transfer materials in solution,few varieties and quantities of acceptor molecules,and single form of charge transfer.Herein,we mainly pay attention to the design,development,preparation and photothermal properties of novel organic charge transfer materials.The main contents are as follows:1.The stability of charge transfer complex in solution is poor and it is difficult to produce strong absorption in the near infrared II region.We utilize supramolecular assembly strategies and fabricate an H-aggregation of 3,3′,5,5′-Tetramethylbenzidine（TMB）–TMB dication(TMB⁺⁺)complexes in linear agarose（H-TTC/LAG）through intermolecular hydrogen-bonding interactions between the amino groups of TTC and the peripheral hydroxyl groups of the LAG.Charge-transfer mechanism and H-aggregation ensure NIR-II absorption of the complex at>1400 nm.The H-aggregation also promotes a non-radiation relaxation pathway and improved the thermal stability of TTC,which together favors the constructed H-TTC/LAG with ultra-efficient PT conversion that can increase rapidly to 140°C in 15 s under the NIR-II laser(1064 nm,1.0 W cm^-2)irradiation.Such a unique H-TTC/LAG with good biocompatibility is used to demonstrate a superior PT therapy via high-efficiency tumor growth inhibition.This is an established H-aggregation of charge-transfer complexes in a noncovalent system,which not only offers a new method to develop efficient NIR-II PT materials but also paves the way for constructing functional materials with aggregates of charge-transfer complexes.2.In addition to supramolecular assembly,cocrystallization of donor and acceptor is a strategy for stabilizing charge-transfer complexes in solution.However,there are limited types and quantities of donors and acceptors in the current charge-transfer eutectic,so it is particularly important to develop new donors and acceptor molecules to construct new charge-transfer cocrystals.Based on this,we construct a unique CT cocrystal by using a persistent 2,2′-azinobis（3-ethylbenzothiazoline-6-sulfonic acid）radical cation(ABTS^+·)as the electron acceptor.The strong persistency and electron affinity of ABTS^+·endow a large electron delocalization degree between ABTS^+·and the TMB donor.Together with the intrinsic long-wavelength absorption of ABTS^+·,the synthesized cocrystal can effectively capture the full solar spectrum and show distinguished photothermal efficiency.Such a cocrystal is further used for solar driven interfacial evaporation,and an evaporation rate of 1.407 kg m^-2 h^-1 and a remarkable solar-to-vapor efficiency of 97.0%have been achieved upon 1 sun irradiation.This work indicates enormous prospects for charge transfer-based functional materials through rational radical cation engineering.3.Although organic radicals have been developed as acceptors for charge-transfer eutectic systems,a single form of charge-transfer in cocrystal systems is sometimes difficult to meet the versatile demands of materials.T herefore,we design and synthesize a stable mixed-valence radical crystal via a surfactant-assisted method,namely TTF-(TTF^+·)₂-RC（where TTF=tetrathiafulvalene）,containing dual CT interactions.The solubilization of surfactants enables successful cocrystallization of mixed-valence TTF molecules with different polarity in aqueous solutions.Short intermolecular distances between adjacent TTF moieties within TTF-(TTF^+·)₂-RC facilitate both inter-valence CT（IVCT）between neutral TTF and TTF^+·,and inter-radical CT（IRCT）between two TTF^+·in radicalπ-dimer,which are confirmed by single-crystal X-ray diffraction,solid-state absorption,electron spin resonance measurements and DFT calculations.Notably,dual CT characters endow TTF-(TTF^+·)₂-RC with strong light absorption over the full solar spectrum and outstanding stability.As a result,TTF-(TTF^+·)₂-RC exhibits significantly enhanced photothermal property,an increase of 46.6°C within 180 s upon one-sun illumination.