Optical Properties,photophysics And Urine Chlorine Sensing Of Low-dimensional Metal Halide Hybrids

Due to the high charge carrier mobilities,longer carrier diffusion length,adjustable band gap,low exciton binding energy and broad light absorption range,the lead halide perovskites show a booming trend in the field of photovoltaic solar cells these years.Compared with three-dimensional（3D）metal halide hybrids（MHHs）,low-dimensional MHHs show more localized exciton with larger exciton binding energy due to the quantum and dielectric confinement effects.However,the structure-property relationship and luminescence mechanism of low-dimensional MHHs are not yet to be well studied,and their applications in biology are rarely reported.In this work,ns²metal-based structure-properties relationships are investigated by means of composition-regulation,induced structural change and molecular design to uncover the underlying photophysical mechanism influenced by distortion,vacancy defects and host-guest interaction,and explore the potential applications in clinic field.The details are as follow.The stereochemical activity of Sb³⁺makes the optical properties of antimony halide hybrid materials highly sensitive response to external stimuli such as temperature,guest molecular and solvents.However,metastable crystals make the structure-properties relationships unclear.In this chapter,we successfully prepared red-emissive(（Ph Pi）₂Sb Cl₇·x H₂O with photoluminescence quantum yield（PL QY）of 32%,which was transformed to two yellow-emissive isomers（Ph Pi）₂Sb Cl₇-V（PL QY:9%）or（Ph Pi）₂Sb Cl₇-S（PL QY:95%）by vacuum-treatment or solvent-induction to remove guest H₂O.Upon placing in open air,both（Ph Pi）₂Sb Cl₇-V（PLQY:9%）and（Ph Pi）₂Sb Cl₇-S can be reversibly transformed into（Ph Pi）₂Sb Cl₇·x H₂O.Based on the reversible phase transformation and the corresponding optical properties of three structures,it was found that the removal of guest molecules would affect the interaction mode between phenyl piperazine cation and halogen anion and changed the excited distortion of the polyhedron.Furthermore,density functional theory（DFT）calculations showed that the efficient triplet luminescence of（Ph Pi）₂Sb Cl₇-S was related to the Jahn-Tell like distortion,which prevents the intersection of ground state and excited state energy surface and inhibits the non-radiative recombination pathway.Different from the emissive origin of the Sb-based MHHs,low-dimensional lead-based MHHs with distorted octahedra usually exhibits dual-emission including one broad-band emission（BE）and narrow emission（NE）from free excitons.Most studies attributed this BE to the recombination of self-trapped excitons（STEs）.The theoretical calculation had confirmed the defect emission.But there is still short of experimental results to support this ideal.In this work,2D[NH₃（CH₂）₈NH₃]Pb Br₄ perovskite microplates（PMSs）with different Br vacancy(V_Br)concentrations were prepared by varying Pb/Br stoichiometry ratio.It was found that the intensity of BE（～522 nm）shows positive correlations with V_Br concentrations.To reveal the underlying mechanism,power-dependent PL and femtosecond transient absorption spectrum（fs-TA）were used to confirm that the luminescence origin from bromide vacancies rather than STEs.Femtosecond transient absorption spectrum first showed that the trapping time of photogenerated electrons by acceptor-like V_Br–is～15 ps,slower than that by surface defects（<1 ps）.This study provided new insight into the underlying mechanism of BE and an effective approach to manipulating the optical properties of 2D perovskites.The PL of 0D MHHs mainly results from the organic polyhedral.As a component of0D MHHs,organic molecular with efficient PL is of great importance in enriching the optical properties of 0D MHHs.However,protonated organic molecular shows an inefficient emission in 0D MHHs.To enhance PL from the organic component of 0D MHHs,N,N,N,N’,N’,N’-Hexamethyl-[1,1’-biphenyl]-4,4’-bromide diamine（HMBBr₂）doped by 3-Hydroxy-1,4-Dimethyl-6-（4-（trimethyl ammonia）phenyl）quinoline-1-ammonium bromide（PQNBr₂）was cocrystallized with Pb Br₂ to obtain 0D MHHs（HMB）4Pb5Br18:PQN with an efficient room-temperature phosphoresce（RTP）which stems from triplet transition of PQNBr₂.Besides,0D MHHs enhanced the electrostatic effect of PQN²⁺and weakened the thermal vibration effect of PQN²⁺,which makes the lifetime of the triplet state emission increase to 3 orders of magnitude.Urinary chlorine is one of the indicators of renal disease.Accurate and rapid detection of urinary chlorine is of great significance for the diagnosis of renal diseases.Here,glycyrrhizin acid（GA）was used to prepare the colloidal ethanol-dispersed Cs Pb Br₃.0.5 g/L PQDs were used as fluorescence probe to detect urine chloride ion based on the fast halogen exchange mechanism.The detection limit was 1.56 m M with a detection range of 10-100 m M..Meanwhile,such fluorescence sensor shows good anti-interference ability to other components in urine such as uric acid and K⁺et al and has great application prospect in clinical detection of urinary chlorine.