Restriction of Intramolecular Motion(RIM):Investigating AIE Mechanism from Experimental and Theoretical Studies

Mechanistic studies promote scientific development from phenomena to theories.Aggregation-induced emission(AIE),as an unusual photophysical phenomenon,builds the bridge between molecular science and aggregate mesoscience.With the twenty-year development of AIE,restriction of intramolecular motion(RIM)has been verified as the working mechanism of AIE effect.In this review,these mechanistic works about RIM are summarized from experimental and theoretical perspectives.Thereinto,the experimental studies are introduced from three parts:external rigidification,structural modification and structural characterization.In the theoretical part,calculations on the low-frequency motion of AIEgens have been performed to prove the RIM mechanism.By virtue of the theoretical calculations,some new mechanisms are proposed to supplement the RIM,such as restriction of access to conical intersection,suppression of Kasha transition,restriction of access to dark state,etc.It is foreseeable that the RIM mechanism will unify the photophysical theories for both molecules and aggregates,and inspire more progress in aggregate science.

(C_(16)H_(28)N)_(2)SbCl_(5):A new lead-free zero-dimensional metal-halide hybrid with bright orange emission

Zero-dimensional(0D)metal halides are in a blossoming status for their fascinating optoelectronic properties.Herein,an antimony-based metal halide of(C_(16)H_(28)N)_(2)SbCl_(5)(C_(16)H_(28)N^(+)=benzyltripropylammonium cations),where the isolated[SbCl_(5)]_(2)−clusters are surrounded by C_(16)H_(28)N^(+)to form a 0D square-pyramidal structure,was synthesized and investigated.The(C_(16)H_(28)N)_(2)SbCl_(5)exhibited a broadband orange emission at 633 nm upon the low-energy irradiation(400 nm)with a near-unity photoluminescence quantum efficiency(97.8%).Interestingly,(C_(16)H_(28)N)_(2)SbCl_(5)showed an additional emission peak at 477 nm upon the higher-energy irradiation(300 nm),which is attributed to the transformation of the doublet of spin-orbit couplings into two independent self-trapped excitons(STEs).Temperaturedependent Raman spectra clearly revealed the characteristics of multi-phonon coupling,demonstrating a strong anharmonic electron-phonon interaction in(C_(16)H_(28)N)_(2)SbCl_(5).Temperature-dependent emission spectra and density functional theory results illustrated that the observed dual-band emission originated from singlet and triplet STEs in[SbCl_(5)]_(2)−units.Combined with the efficient emission and excellent stability of(C_(16)H_(28)N)_(2)SbCl_(5),a stable white-light-emitting diode with an ultra-high color rendering index of 96.6 was fabricated.

Metal cation substitution of halide perovskite nanocrystals

Recent years have seen a rapid development of lead halide perovskite(LHP)nanocrystals(NCs)as new and promising functional nanomaterials,which exhibit strong potential in a wide range of optoelectronic applications due to their superior properties and solution-processable advantages.However,to promote their progress in commercialization,overcoming the drawbacks of intrinsic lead toxicity and optimizing material performance are important and must be solved using alternative metal ions to replace Pb ions.In this review,we primarily summarize the recent development of lead-substitution strategies,which focus on the commonalities and differences of their functionalities that are induced by various doped ions.After a brief introduction to the synthesis,nucleation and growth of all-inorganic LHP NCs,a deep discussion of the crystalline structure,electronic band structure,defect states,exciton binding energy,exciton photodynamic process and stability is followed.Specifically,we highlight the importance of both theoretical calculations and experimental characterizations to establish indicative guidelines for high-performance semiconductor nanomaterials.Finally,the light emission applications are discussed,and several issues concerning future research on the controllable synthesis of halide perovskite NCs with low toxicity,superior reproducibility and properties are outlined.