Transform ACQ Luminophores To AIEgens Via Engineering The Variable C-C Bonds Of O-carboranes In Fluorescent Cores

Conventional luminophores often suffer undesirable ACQ effect due to π…πstacking interactions in aggregate state,which has a crucial limitation in material application.People suffer from this detrimental effect until a new phenomenon was found by Prof.Tang,an anti-ACQ photophysical phenomenon which was named as AIE(Aggregation-Induced Emission).Since then,chemists devoted themselves to reveal the mechanism of AIE and expand its applications.So far,RIM(Restriction of Intramolecular Motions)proposed by Prof.Tang could explain a variety of AIE molecules.To explain it elaborately,the restriction of intramolecular vibrations and rotations blocks the non-radiative pathway and produces effective luminescence in aggregates.According to recent progress,people have drawn much attention to o-carborane derivatives which usually quench luminescence in solution.o-Carborane is an icosahedral cage with two adjacent carbon cites.The vibration of C-C bond and the rotation of o-carborane cage could provide a non-radiation channel,which results in weak luminescence in solution.It is worth noting that the photophysical phenomenon of o-carborane can be well explained using RIM.In other words,o-carborane may be an AIE-active molecule in potential.Hence,in this work,the variable C-C bond of o-carborane cage was treated as a vibrational factor to synthesize AIE-active o-carborane luminophores.9-Phenylanthracene which possesses ACQ effect was utilized as a model compound.Four o-carborane derivatives o-et-an,o-an,o-me-an and ph-o-an were synthesized by modifying the substituents both in phenyl group and carboranyl group.Although a donor-acceptor structure was found and charge transfer emission could be observed in PL spectra due to the electron-withdrawing ability of o-carborane,the dramatic change of C-C bond in o-carborane still led to a rather weak luminescence in solution.Therefore,AIE PL spectra was carried out for all the compounds.The results revealed two ACQ compounds o-an and o-me-an,another two AIE molecules o-et-an and ph-o-an.The results indicate that it is an effective strategy to tune photophysical properties by engineering of variable C-C bonds of o-carborane cores in the fluorescent molecules.Different substituents(H,ethyl and phenyl)in o-carboranes could remarkably affect its vibration performance,thus,transformation from ACQ to AIE can be realized.