Synthesis And Luminescent Properties Of Sulfur Residing Nonaromatic Compounds

The recent research on emissive materials emphasizes the utility of organic luminescent materials because of their discriminative characteristics potential implications in organic lightemitting diodes(OLEDs),biological imaging,display screens,optical devices,biological and chemical sensing,etc.To date,many endeavors are put into the light-emitting research field to fabricate the exact mechanism of intrinsic luminescence and have postulated many conjectures on diverse nonconventional luminogens.No doubt,these theories can be applied to many emissive systems,however,there are still some defects.To further investigate and support the luminescence mechanism of novel and emerging nonconventional systems,a concise set of principles is urgently required.Such emission behaviors are similar to common nonconventional luminogens,and can be well rationalized by the clustering-triggered emission(CTE)mechanism.Namely,clustering of diverse subunits like amine,carbonyl,and other functional side groups extended electron delocalization and thus enhanced the conjugation together with simultaneously rigidified conformations.Nowadays,it has been noticed that sulfur containing nonconventional chromophores(sulfide,sulfoxide and sulfone)have attracted intensive attention in the luminescent world for their noteworthy and valuable applications.Heretofore,in this dissertation,the photophysical properties of sulfur containing nonconventional polymers and small molecules have been explored,and photophysical properties of different concentration of solutions and varied states of solids at different temperatures are studied in depth and also its luminescence mechanism has been discussed that proved its application explosive detection and other fields.The major research contents are summarized as follows:(1)Nonaromatic photoluminescent polymers have attracted great attention due to their intriguing photophysical properties and promising implications in optoelectronic and biological areas.The luminescence from these nonconventional luminophores can be well rationalized by the clustering-triggered emission mechanism.According to the CTE mechanism,discrete chromophores with π and/or n electrons play an important role in realizing atypical luminescent groups.Among them,the carbon group is considered to be a very important candidate group.Apart from this,the thiol functional group is also considered to be a promising chromophore owing to its similar and greater π and n electrons.Sulfur,although an n-electron-rich element with a big radius,hasn’t been widely utilized in the construction of nonconventional luminophores despite its potential competitiveness in nonaromatic photoluminescent polymers.Large-sized thiols can acquire efficient aggregation due to good electronic delocalization,thereby enhancing their intrinsic emission.Herein,the “click” type Michael polyaddition is utilized to construct sulfurbearing nonconventional luminophores,and two sulfur enriched nonaromatic poly(thioether sulfone)s(PES)are obtained,which demonstrate fluorescence-phosphorescence dual emission.More investigations concerning the monomer of bis(vinylsulfonyl)methane are further proceeded to support acquired results.Finally,the application of explosive detection by the prepared PES is also conducted.These polymers with sharp photophysical properties are envisaged as the gateway to new horizons of constructing striking nonaromatic polymers that impart promising applications in optoelectronics.(2)Nonconventional luminophores without large conjugated structures are attracting increasing attention for their unique aggregation-induced emission(AIE)properties and promising applications in optoelectronic and biomedical areas.The emission mechanism,however,remains elusive,which makes rational molecular design difficult.Herein,based on the CTE mechanism,nonaromatic polymers containing multitype heteroatoms(i.e.,O,N,and S)and involving amide(>CONH)and sulfide(-S-)groups were designed and synthesized through facile thiol-ene click chemistry.Two polymers were synthesized through the Michael polyaddition approach using dithiols and diacrylamides.The resulting polymers demonstrated typical concentration-enhanced emission,AIE phenomenon,and excitation-dependent emission.Notably,compared with polysulfides,these polymers exhibited much higher solid-state emission efficiencies,because of the incorporation of amide units,which contributed to the formation of emissive clusters with highly rigidified conformations through effective hydrogen bonding,resulting in solid-state luminescence efficiencies of 10% for both the polymers,which are higher than the previously reported polysulfide(4.5%)and polysulfoxide(7.0%).Thus,a hydrogen bonding method is provided to enhance the intrinsic emission of nonaromatic sulfur residing polymers.Furthermore,distinct persistent cryogenic phosphorescence or even room temperature phosphorescence(RTP)was noticed.These photophysical behaviors can well be rationalized in terms of the CTE mechanism,indicating the feasibility of rational molecular design and luminescence regulation.(3)Because of the bigger atomic radius,sulfur has greater electronic cloud density and ability to exhibit variable oxidation states.In addition,oxygen atom is electron rich owing to lone pair of electrons(n).Considering the heavy atom effect of sulfur,its combination with oxygen atom can create a more efficient electronic interactions,thereby enhancing its emission properties,which can be named oxidation enhanced emission(OEE).At present,there are few reports on luminescent sulfur clusters,therefore,is will be an important approach to construct nonconventional luminescent compounds in future.Therefore,we investigated sulfur encompassing nonaromatic luminescent small molecules(thiosulfonylmethane)(TSM)and their controlled oxidation to prepare sulfoxide(S=O)and sulfone(O=S=O),which display remarkable luminescence.Surely after introducing electron rich oxygen atoms,sulfur is oxidized to S=O and O=S=O,the oxidized products laid out a new intellect for fluorescence(FL)with enhanced emission intensity,and endorsed oxidation enhanced emission(OEE)mechanism.Solutions of different concentrations were tested for fluorescence.The most concentrated solution was recognized with brighter emission from all the rest of less concentrated solutions by reason of greater amounts of emissive centers.In addition,the CTE mechanism was reasonably revealed from powdered compound because its luminescence brightness reaches a larger value.To further verify the experimental results and selective binding mechanism of thiosulfonylmethane(TSM),we also performed density functional theory(DFT)calculations.The single crystal of BETBESM and its DFT calculations sufficiently supplied prove for steric interactions and through-space interaction and conjugation of electronic cloud among luminogenic chromophores.Furthermore,picric acid(PA)was used for emission quenching of BVSM and the results show that it is useful for implication as an explosive detector in the instruments used for security check.Therefore,this study with unique design and photophysical character could be implied for fabricating modified and also entirely different unconventional luminescent materials.