| Persistent room temperature phosphorescence?p-RTP?has drawn extensive attention due to their unique photophysical processes and promising applications in organic light emitting diodes?OLEDs?,biological areas,data recording,chemical and biological areas.Pure organic p-RTP luminogens take advantages of long lifetime,good biocompatibility,good processability,low cost and wide variety,allowing a wide range of optoelectronic and biological applications.Exciting advancements have been made in the past few years,generally,there are two attempts to achieve efficient p-RTP:one is to boost the spin-orbit coupling?SOC?and subsequently promote the intersystem crossing?ISC?processes through incorporation of heavy atoms,heteroatoms,or aromatic carbonyls;the other is to stabilize the triplet excitons in a rigid environment by suppressing nonradiative decay pathways to activate the RTP emission,such as crystal formation,embedding into rigid hosts,polymer assistance,and metal–organic framework?MOF?.Based on the above considerations,this thesis is dedicated to designing and preparing a series of pure organic room temperature phosphorescence materials based on carbazole,aromatic carbonyl and isophthalic acid molecular structure.At the time of getting excellent performance,we strive to further investigate and clarify the structure-property relationship,providing feasible design strategies for similar materials.Details are as followings:The strategy starts from 9H-acetyl carbazole?ACZ?,a p-RTP dye with?p and<?>p of0.4%and 174.4 ms,respectively.Benzene ring was incorporated to introduce further?orbitals,additional carbonyl group was introduced to enhance SOC,according to the above design strategy,we successfully designed and synthesized a series of bisamide compounds named DCED,o-PBCM,m-PBCM and p-PBCM based on raw materials of carbazole and a series of acyl chloride molecules.The results show that these four compounds simultaneously emit both fluorescence and persistent phosphorescence at room temperature.Especially for m-PBCM,the recrystallized solids demonstrate bright emissions,giving impressively efficient p-RTP with<?>p of up to 710.6 ms.All of the compounds have considerable quantum yields,the?c value of o-PBCM is determined as 23.6%,its?ps is calculated to be 10.2%,indicating its efficient p-RTP emission.The natural transition orbital?NTO?images of the lowest excited singlet states?S1?,the lowest excited triplet states?T1?and T2 states of the four materials indicated that their RTP are mainly originated from carbazole.DCED and m-PBCM show high contrast mechanochromism upon heavily grinding with a pestle,due to the conversion from crystalline to amorphous state.Astonishingly,even upon heavily grinding and exposuring to external quenchers?i.e.O2?,m-PBCM and p-PBCM can still afford yellow p-RTP lasting for several seconds at ambient conditions,which is rarely found in the former reports,which is extraordinarily desirable for real applications in anticounterfeiting,encryption,and bioimaging.Isophthalic acid?IPA?is a typical ultralong room temperature phosphorescence molecule with the advantages of low cost and easy to obtain.We modified it with heavy atom,esterification and bonded it with carbazole group to obtain two molecules,named DCIZ and CZIA,which have ultralong room temperature phosphorescence.As for CZIA,the X-ray diffraction depicts nearly flat lines or broad diffractions with extremely weak intensity,suggestive of its disordered amorphous nature,with impressively efficient p-RTP with<?>p of up to 593.7 ms.Different from the previous reports about crystallization-induced phosphorescence?CIP?,this single molecule with p-RTP at amorphous state is rarely achieved.-COOH groups are capable of forming inter-hydrogen bonding networks,which can form a rigid system to suppress molecular motions and thus to enhance RTP effect,providing design strategies to achieve amorphous persistent and robust room temperature phosphorescence without host. |
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