The Molecular Design Of Unconventional Room Temperature Phosphorescent Materials And Study Of Luminescent Mechanism

The pure organic room temperature phosphorescent?RTP?materials have a wide application in the fields of organic light emitting diode?OLED?,sensors,biological imaging and security anti-counterfeiting because of the excellent optical properties,wide variety,easy modification and low toxicity.At present,most of conventional pure organic RTP materials containing large?-conjugated system with aromatic groups have the problems of complex preparation process,high cost and difficult to scale production.However,the unconventional RTP materials without aromatic groups have attracted more and more attention due to the advantages of environmental friendliness,simple preparation and low cost.But the research on unconventional RTP materials is still in the initial stage with indistinct luminescent mechanism.And the reported unconventional RTP materials are mostly found by accident without unified and feasible theoretical basis.In this paper,the luminescent properties and structures of unconventional RTP materials with different auxochrome are studied to explore the luminescent mechanism.Moreover,the new unconventional luminescent materials are constructed,and the applications in sensors are explored.The main research contents are as follows:?1?First,the photophysical properties of methanol?MeOH?,ethanol?EtOH?,ethylene glycol?EG?,glycerol?GL?,pentaerythritol?PER?,1,3-adamantane glycol?AAG?and polyvinyl alcohol?PVA?were studied.The results showed that the liquid alcohol hydroxyl compounds?MeOH,Et OH,EG and GL?at room temperature had no obvious RTP emission behavior,but they emitted obvious phosphorescence at low temperature?77K?.However,the solid hydroxyl compounds?PER,AAG and PVA?at room temperature possessed obvious RTP emission.Next,the structural optimization and theoretical calculation were analyzed via density functional theory?DFT?and time-dependent density functional theory?TD-DFT?.The resluts showed that hydroxyl compounds obtained large spin-orbit coupling constant?SOC?and smaller energy difference between the excited singlet and excited triplet states,indicating that hydroxyl groups were beneficial to the construction of RTP materials.?2?The clustering between hydroxyl groups is beneficial to enhance the emission of RTP.Cellulose is a common natural polymer material with a large amount of hydroxyl groups.Therefore,the photophysical properties of cellulose?MCC?and its derivatives?hydroxyethyl cellulose?HEC?,hydroxypropyl cellulose?HPC?and cellulose acetate?CA??were researched.The results showed that MCC,HEC and HPC with large amounts of hydroxyl groups were RTP materials.However,the luminescence of CA was weak or even non-luminous at room temperature.The resluts further proved the universality of mechanism that hydroxyl groups were beneficial to the construction of unconventional RTP materials.Moreover,HEC enbled to be used for the detection of 2,4,6-trinitrophenol?TNP?and was an environment-friendly probe for TNP detection.?3?The long lifetime is very important for the application of RTP materials in the fields of biological imaging,dynamic diagnosis and treatment,drug delivery and so on.Sodium carboxymethyl cellulose?CMC-Na?,as a derivative of cellulose,also have obvious RTP.In order to further improve the lifetime of CMC-Na,the cellulose-based RTP material CMC-Zn with long lifetime was prepared by cross-linking between Zn²⁺and CMC-Na.The structure of CMC-Zn was characterized by EDS and FT-IR,and the photophysical properties of CMC-Zn and CMC-Na was studied.The results showed that the lifetime and luminous quantum efficiency of CMC-Zn had been significantly improved to 281 ms and 16.5%,respectively.Thus,the results indicated that the ionic bonds could be used for the construction of long-lifetime RTP materials without precious metals.?4?The chitosan?CTS?is an environmentally friendly polymer with the similar structure to cellulose.The molecular chains contain hydroxyl groups and amino groups.Therefore,the the photophysical properties of CTS were further studied,and the structure optimization and theoretical calculation were carried out.The results showed that CTS was also RTP material with the lifetime of 1.38 ms.At the same time,CTS had obvious light emission in solid state and concentrated solution,but the emission was weak in dilute solution with aggregation induced emission?AIE?effect.Because the lone pair electrons on the hydroxyl groups and amino groups could enhance the spin-orbit coupling,resulting the improvement of the intersystem crossing and the emission of phosphorescence.In addition,CTS had the characteristic of specific recognition to Fe³⁺and was useful for the detection of Fe³⁺.?5?The unconventional luminescent materials with delayed fluorescence emission were constructed via guanidine groups?1,2-dicyanoguanidine ethane?CGE?and 1,4-dicyanoguanidine butane?CGB??.Firstly,the structures of the compounds were characterized by nuclear magnetic resonance spectroscopy?NMR?and Fourier transform infrared spectroscopy?FT-IR?,and the photophysical properties of the powders,solutions and doped films at room temperature and low temperature were studied.The results showed CGE and CGB had obvious obvious delayed fluorescence emission.And the lifetimes at room temperature are 1.21 ms and 0.81 ms,respectively.In addition,structural optimization and theoretical calculation were analyzed by DFT and TD-DFT.The results showed that CGE and CGB obtained the ability of intersystem crossing and enabled to emit the afterglow,which indicated that guanidine groups were very effective for the construction of unconventional luminescent materials.And the preparation of unconventional luminescent materials with delayed fluorescence emission enriches the types of unconventional luminescent materials.