| The development and progress of functional materials have brought a big advantage for improving people’s production and life.Among them,organic small molecule functional materials are favored because of their diverse structure,easy regulation,simple synthesis,low cost and convenient large-scale preparation.On the one hand,solar-driven water evaporation system can be constructed utilizing organic photothermal conversion materials as light absorbent.On the other hand,organic light-emitting devices（OLED）can be fabricated basing on organic luminescent materials.All in all,whether the organic solar absorbers functioned in solar-driven water evaporation system or the organic red emitters applied in OLED are inseparable from the exploration and research of narrow band gap materials.Quinoxaline derivatives withπ-conjugated structure and electron affinity have attracted much attention because of their simple synthesis,good stability,unique properties and easy modification.Therefore,in this thesisi,a series of organic small molecule multifunctional materials with photothermal or electroluminescent properties were constructed with quinoxaline core through reasonable modification.The main contents are as follows:In Chapter 2,the author designed a novel donor-acceptor（D-A）type photothermal material DDPA-PDN with narrow band-gap and wide absorption band（300～850 nm）through connecting a common donor group diphenylamine and a new acceptor core dibenzo[a,c]naphtho[2,3-h]phenazine-8,13-dione（PDN）with conjugate rigid planar skeleton which was obtained by fusing dibenzo[f,h]quinoxaline and anthraquinone units together.The appearance of charge transfer state formed by the effective electron delocalization of the D-A structure together with theπ-πstacking of the aggregated state supported by the conjugated rigid plane structure greatly redshift the absorption spectrum of DDPA-PDN which thus overlaps considerably with the solar spectrum.According to the energy gap law,the resulting small energy gap can facilitate non-radiative decay processes,allowing light energy captured by molecules to be converted into heat energy.Then DDPA-PDN was loaded on cellulose paper with abundant water microchannels to prepare the solar absorber for the construction of solar-driven water evaporation system.Under 1 k W m-2 solar irradiation,the water evaporation rate and efficiency of the SDWE system achieved 1.07 kg m-2 h-1 and 73.98%,respectively.In addition,DDPA-PDN was coated on the surface of thermoelectric equipment as solar absorber to prepare thermoelectric power generation device.Under 5 k W m-2 solar irradiation,the voltage generated is as high as 148 m V.This study demonstrated for the first time the application of D-A type organic small molecule materials with narrow band-gap in water evaporation and thermoelectricity.In Chapter 3,the author designed two new D-A type photothermal materials with umbrella-like structure,t-GDPA-CNQ and meo-GDPA-CNQ,which were obtained through benzene bridge linking the electron donating unit diphenylenediamine derivatives with the acceptor core 2,3-dicarbonitrile-quinoxaline（CNQ）.The"umbrella"structure increasedπconjugation and steric hindrance of the molecules,contributing to the long wavelength absorption and molecular motion in the aggregated state,thus promoted non-radiative decay process and achieved the purpose of converting light energy into heat energy.Based on the narrow band-gap and wide absorption band（200～1100 nm）in the aggregated state of t-GDPA-CNQ and meo-GDPA-CNQ,solar-driven water evaporation devices were prepared,which showed water evaporation rate and efficiency as 1.21 kg m-2 h-1（82.51%）and 1.33 kg m-2 h-1（82.52%）,respectively,under 1 k W m-2 solar irradiation.After that,the two materials were coated on the surface of the thermoelectric equipment as solar absorbing materials to prepare the thermoelectric power generation device.Under 5 k W m-2 solar irradiation,t-GDPA-CNQ and meo-GDPA-CNQ produced voltage up to 245 m V and 275 m V respectively.This study further constructed two D-A type organic small molecule photothermal materials with smaller band-gap and wider absorption band by increasing molecularπconjugation.At the same time,the effect of molecular motion on the photothermal properties of molecules was studied by introducing large steric hindrance structure.In Chapter 4,the author designed two new D-A type multifunctional materials with narrow band-gap,t-GDPA-QCN and meo-GDPA-QCN,which were obtained through benzene bridge linking the electron donating unit diphenylenediamine derivatives with the acceptor core quinoxaline-6,7-dicarbonitrile（QCN）.On the one hand,t-GDPA-QCN and meo-GDPA-QCN showed similar photothermal properties with wide absorption bands（200～1200 nm）and non-emission characteristics in the aggregated state.Based on this,solar driven water evaporation device and thermoelectric power generation device were prepared.Under 1 k W m-2 solar irradiation,the water evaporation rate and efficiency of t-GDPA-QCN and meo-GDPA-QCN are 1.19 kg m-2 h-1（81.29%）and 1.21 kg m-2 h-1（82.52%）,respectively,and the generated voltages are 71 m V and 73 m V,respectively.On the other hand,due to the emission characteristics in restricted environment and good evaporation stability of t-GDPA-QCN,electroluminescent devices were prepared by doping t-GDPA-QCN in 1,3-di（9H-carbazol-9-yl）benzene（m CP）host matrix.When the doping concentration is 3%,the device exhibits deep red emission at 664 nm,and the maximum external quantum efficiency reaches 3.20%.This study constructed two D-A type organic small molecule photothermal materials with narrow band gap and wide absorption band by regulating the distance between the donor and acceptor,and realized for the first time the application of the same molecule in solar driven water evaporation system and organic light-emitting devices.In Chapter 5,the author designed a novel D-A type red-near infrared emitting material DPA-AQN-TRZ with narrow band-gap through benzene bridge linking an acceptor unit diphenyltriazine and a donor unit diphenylamine with an acceptor core acenaphtho[1,2-b]quinoxaline-9,10-dicarbonitrile（AQN）.The introduction of diphenyltriazine and diphenylamine groups in AQN with rigid planar structure can effectively inhibit the molecular motion and reduce the non-radiative transition.While the introduction of two strong electron-absorbing cyanogen groups and large conjugated triazine groups can reduce the LUMO level of the molecule and facilitate the long wavelength emission.Interestingly,DPA-AQN-TRZ exhibited significant stimulus chromism,with emission wavelengths varying as high as 178 nm.In order to explore the electroluminescent properties of DPA-AQN-TRZ,doped and undoped OLEDs were prepared using DPA-AQN-TRZ as the luminescent layer.The device with a doping concentration of 10 wt%achieved a maximum EQE of 17.22%at 613 nm.The undoped device achieved a maximum EQE of 2.77%and a low efficiency roll-off in the near infrared region of 700 nm.This work constructed a new D-A type organic small molecule materials with red-near infrared emission by regulating molecular structure to limit molecular motion,which provides an effective design strategy for the study of efficient red emitters and non-doping OLEDs. |
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