Design,Synthesis And Luminescence Properties Of Novel Carborane Complexes Based On Tetraphenylethylene

Carboranes are icosahedral boron clusters with a three-dimensional quasi-aromatic structure of the electrons,which have unique properties,such as highly polarizable ?-aromatic character,high thermal and chemical stability,and special photophysical and electronic properties that make them useful in biomedical applications and material science.One of the more recent uses of boron clusters in materials science is the preparation of luminescent materials.In the past decade,several groups have been interested in combining organic ?-conjugated systems with carborane derivatives,in order to modulate their electronic,optical,and/or photophysical properties.Our group has also contributed,with rather small conjugated ligands,anthracenes,in engineering anthracene-carborane systems for material applications.In the quest of possible luminescent systems,we selected compounds with relevance in organic optoelectronics.In fact,in the last few years,compounds that show fluorescence enhancement in the solid state have attracted significant interests due to their applications in biosensing and optoelectronics.In 2001,Tang and co-workers found an extraordinary phenomenon that silacyclopentadiene was non-luminescent in the solution,but emited greatly in the aggregate state,which was later termed with AIE(aggregation induced emission).In the past decade,with the worldwide efforts of scientists,AIE based materials have experienced a huge development.Tetraphenylethylenes(TPE)are archetypal AIE-active luminogens,which have been extensively studied and utilized in bioprobes,chemical sensing,and optoelectronic systems.In this paper,we have combined TPE with carborane unit,and synthesized a series of functional compounds materials with AIE characteristics.Properties of the synthetic compounds have been studied,and the details are outlined as follows:(1)Four o-carborane-modified TPE derivatives have been synthesized for the first time,referencing TPE as the model compound.Our experimental data revealed that the introduction of rigid and bulky carborane cages into TPE-cores has led to high quantum efficiency in solid state.By changing the 2-R-group at the carborane unit with-H,-CH3 or phenyl group,we can manipulate luminescent quantum yields from 18%to 63%of the corresponding TPE derivatives in solid state,while the emission color also exhibits an evident shift from blue to yellow(115 nm red-shift).Besides,density functional theory(DFT)and time dependent DFT(TD-DFT)calculations have been successfully applied to investigate the excited-state electronic structures of the carborane-modified TPEs.(2)A novel TPE-brige-TPE triad has been constructed,where the o-carborane moiety functions as central brige and two AIE-active TPE units are in the lateral positions.This molecular triad was characterized by various spectroscopic methods,and its structure has been studied by X-ray crystallography as well as theoretical calculations.The impact of carborane linker upon the AIE characteristics of TPE-brige-TPE triad has been investigated.When altering the central brige from linear brige to three-dimensional brige,the luminescent quantum yields of TPE-brige-TPE triads can be manipulated from 12%to 55%in the solid state,with the luminescence color tuned from blue to yellow.