Molecular Folding-Induced Pure Organic Room-Temperature Phosphorescence Enhancement:Mechanism And Applications Exploration

Pure organic room-temperature phosphorescence（RTP）materials have demonstrated significant potential in various applications,including displays,lighting,encryption,anti-counterfeiting,sensing,detection,and bioimaging due to their low cost,long lifetime,and customizable luminescent properties.The generation of RTP not only requires triplet excitons facilitated by intersystem crossing（ISC）but also relies on radiative and non-radiative transitions from the lowest triplet state（T₁）to the ground state（S₀）.Furthmore,the luminescent properties of RTP materials,including efficiency and lifetime,are significantly influenced by spin-orbit coupling（SOC）between singlet and triplet states.In pure organic materials,the absence of the heavy atom effect results in weak SOC,leading to lower RTP efficiency.Therefore,how to enhance the SOC of pure organic materials to improve the RTP efficiency has emerged as a significant scientific challenge in this field.In 2018,we introduced the concept of“folding-induced spin-orbit coupling enhancement”to address this issue.Further research is needed to systematically verify the experimental results and reveal the mechanism in depth.In addition,we will also explore novel molecular designs to create organic RTP materials with high efficiency,adjustable color and lifetime,to further enrich material systems and expand their functional integration and intelligent applications.Based on the above concepts,in this dissertation,we design and construct model molecules with varying folding angles to investigate the correlation between molecular folding degree and RTP luminescence efficiency.The study also explores the theoretical simulation of the relationship between SOC and molecular folding angles,providing insight into the essential characteristics of changes in the excited state.Additionally,high-pressure experiments are conducted to adjust molecular folding degrees,observing changes in RTP properties,aiming to validate the“folding-induced SOC enhancement”mechanism.Additionally,this dissertation introduces innovative molecular design concepts,leading to the development of property-tunable,high-performance,and multifunctional pure organic RTP materials.Furthermore,the dissertation deeply explores the unique characteristics and advantages of these materials,with a specific focus on oxygen as a triplet exciton quencher.Various potential applications such as oxygen sensing,light-induced dynamic tags,time-dependent encryption technologies,and visualization of phase separation analysis in blend polymers are discussed.Overall,this dissertation aims to provide a new mechanism for enhancing SOC in pure organic materials,offer a novel strategy for molecular design to adjust luminescent properties in pure organic RTP materials,and present new application scenarios for these materials.The specific research contents of this dissertation are as follows:1.Constructed model molecules with varying folding angles using thianthrene,phenoxathiine,dibenzo-1,4-dioxin,and benzo[b]benzo[4,5]thieno[2,3-d]thiophene.Investigated the correlation between molecular folding angles and RTP properties.The mechanism of folding-induced SOC enhancement was elucidated through theoretical calculations:molecular folding results in the decoupling of lone-pair electrons on heteroatoms from the molecular planeπorbitals,leading to distinct ¹（9）9),^*)and¹（9）9),^*)excited state characteristics compared to ³（,^*）,thereby significantly enhancing SOC.Furthermore,synthesized selenanthrene crystals with a folding configuration akin to thianthrene,exhibited pure phosphorescent emission.By conducting high-pressure experiments,the manipulation of molecular folding angles in selenanthrene crystals was achieved,unveiling a pressure-induced enhancement of pure organic RTP.These findings offer compelling evidence that increasing molecular folding promotes SOC enhancement,consequently elevating RTP,thereby validating the mechanism of folding-induced SOC enhancement.2.In accordance with the folding-induced SOC enhancement theory,a series of oxygen-sensitive pure organic RTP materials were developed by making simple conjugation modifications to the thianthrene unit and extending the folding units.These materials exhibited both fluorescence and phosphorescence emissions,allowing for the quantitative detection of oxygen concentration via ratio-metric optical analysis.Compared to traditional metal-organic phosphorescent materials,these materials offer advantages,such as lower cost,higher oxygen sensitivity,and more excellent substrate adaptability.With a simple change in the substrate,high-sensitivity oxygen detection across various concentrations can be achieved.To address practical application requirements,a real-time detection method of oxygen concentration based on video imaging was proposed.The construction of the necessary simple device and programming was completed,enabling quantitative oxygen concentration detection without requiring a spectrometer,thus providing significant cost and efficiency advantages.3.The“functional unit combination synergy strategy”was proposed to design and construct luminescence-tunable pure organic RTP materials.The strategy involves combining folding units with luminescent units that have distinct characteristics,such as color and lifetime.By utilizing the folding units to enhance the molecular SOC,precise control over the luminescent properties of high-performance pure organic RTP materials can be achieved.Following this approach,a series of pure organic RTP materials with various colors and lifetime were synthesized.These materials exhibited unique light-induced phosphorescence responsiveness with good cyclicity and stability due to intrinsic oxygen consumption caused by continuous irradiation.Leveraging these dynamic light-responsive characteristics,innovative applications were explored,including light-writable dynamic tags,time-dependent“4D”encryption,and visualization of phase separation in blend polymers,thus broadening the applications of pure organic RTP materials.