Non-adiabatic conformation distortion charge transfer enables dual emission of thermally activated delayed fluorescence and room temperature phosphorescence.

In this work, we report for the first time that thiophenol-substituted naphthalimide can achieve thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) simultaneously through non-conjugated flexible connection. Herein, we explain that the enhancement of intersystem crossing (ISC) between the singlet excited state and triplet excited states in NISPh is mainly caused by the non-adiabatic conformation distortion charge transfer (CDCT) of the excited states. More precisely, CDCT results in the conformation matching and energy barrier decrease between the excited states. In addition, the electronic and vibration coupling is further enhanced in NISPh. Our work substantiates a rational design strategy for the development of simple purely organic materials to achieve dual emission of TADF and RTP.

Aqueous-phase dual-functional chiral perovskites for hydrogen sulfide (H2S) detection and antibacterial applications in Escherichia coli.

Perovskite nanocrystals (PNCs) have attracted extensive attention for their potential applications in biology. However, only a handful of PNCs have been scrutinized in the biological domain due to issues such as instability, poor dispersion, and size inhomogeneity in polar solvents. The development of dual-functional perovskite nanomaterials with hydrogen sulfide (H2S) sensing and antibacterial capabilities is particularly intriguing. In this study, we prepared chiral quasi-two-dimensional (quasi-2D) perovskite nanomaterials, Bio(S-PEA)2CsPb2Br7 and Bio(R-PEA)2CsPb2Br7, that were uniformly dispersed in aqueous media. The effective encapsulation of methoxypolyethylene glycol amine (mPEG-NH2) improved water stability and uniformity of particle size. Circular dichroism (CD) signals were created by the successful insertion of chiral cations. These perovskites as probes showed a rapid and sensitive fluorescence quenching response to H2S, and the effect of imaging detection was observed at the Escherichia coli (E. coli) level. As antibacterial agents, their pronounced positive charge properties facilitated membrane lysis and subsequent E. coli death, indicating a significant antibacterial effect. This work has preliminary explored the application of chiral perovskites in biology and provides insight into the development of bifunctional perovskite nanomaterials for biological applications.

Room-temperature efficient photoluminescence mechanism of indium doping lead-free colloidal MA3Bi2Br9 quantum dots solution.

Lead halide perovskite quantum dots (QDs) are promising candidates for future optoelectronic devices due to their excellent photonic and electronic properties. However, poor stability and toxicity problems limit their further development. This work demonstrates the doping tactics to boost the optical properties of lead-free colloidal MA3Bi2Br9 QDs, the indium ion (In3+) doping presented herein is found to be effective in improving the photoluminescence (PL) properties of MA3Bi2Br9 (CH3NH2 = MA) QDs without alerting their favorable electronic structure. It has been elucidated by microscopy and diffraction results that the In3+ doping optimizes the QDs solution octahedron structure, and the PL red-shifted phenomenon coincides well with the analogous red-shifted obtained in the ultraviolet/visible (UV-Vis) absorption spectroscopy, which is due to the quantum confinement effect. And the nanosecond transient absorption (ns-TA) spectroscopy elucidates that the enhanced radiative recombination process contributes to enhanced stability and luminescence. The photoluminescence quantum yield (PLQY) of MA3Bi2Br9 QDs is increased by 60.7%. This work offers a valid strategy for improving the quality of the lead-free perovskite QDs.

Lead-Free Zero-Dimensional Zn-Based Metal Halides of Highly Efficient Blue Luminescence from Self-Trapping Exciton.

Recently, hybrid metal halides have received great attention in the field of solid-state lighting because of their diverse structures and excellent photoluminescence properties. In this work, we first reported two hybrid zinc-based metal halides with zero-dimensional structures, (BMPP)2ZnBr4 and (TBA)2ZnBr4, which exhibited broadband emission with large Stokes shifts. Notably, the highest photoluminescence quantum yield of 59.76% was observed. Additionally, the luminescence mechanism of metal halides was investigated by using time-resolved femtosecond transient absorption experiments. A broad excited-state absorption platform with the tendency of slowly decaying was shown in the detection range, demonstrating that after the electrons were excited to the excited state, the free excitons underwent a nonadiabatic transition to self-trapped excitons and went through a radiation recombination process to the ground state. A blue-light-emitting diode could be easily obtained by coating (BMPP)2ZnBr4 on a GaN chip, which indicated that it has good competitiveness in the application of solid-state lighting devices.

Insight into efficient photoluminescence regulation mechanism by lattice distortion and Mn2+ doping in organic-inorganic hybrid perovskites.

The space configurations of organic ammonium cations play a vital role in indirectly revealing the relationship between the structures and photoluminescence properties. Structural transformation induced tunability of the photophysical properties has rarely been reported. In this work, two organic-inorganic halide perovskites with different octahedral distortions were synthesized to explore the relationships between "steric effect" of organic cations and photoluminescence properties. The broadband emission of (DETA)PbBr5·H2O with high octahedral distortion is attributed to self-trapped excitons and trap states, whereas smaller steric hindrance ammonium cation 1,4-butanediamine form a 2D layered perovskite with narrowband emission due to free excitons. More importantly, the photoactive metal ions Mn2+ doping strategy gives rise to tunable broadband light emission from weak to strong orange emission with higher PLQY up to 20.96 % and 12.90% in 0D (DETA)Pb0.2Mn0.8Br5·H2O and 2D (BDA)Pb0.8Mn0.2Br4 respectively. Combined with time-correlated single photon counting and photoluminescence spectra, Mn-doped perovskites reveal energy transfer from host to Mn2+ characteristic energy level (4T1-6A1). Importantly, defect states are reduced by doping manganese ions in (DETA)PbBr5·H2O to enhance photoluminescence intensity. This work sheds light on the mechanism of defect-related emission and provides a successful strategy for designing novel and adjustable materials.

Ultrafast non-adiabatic dynamics of stilbene-based plant-derived sunscreens with cis-trans isomerization structures.

In this work, we investigated the potential UV protection mechanism of the natural compounds hydroxy resveratrol and pterostilbene by combining theoretical calculations and femtosecond transient absorption spectra (FTAS). The UV absorption spectra showed that the two compounds exhibited strong absorption properties and high photostability. We found two molecules will reach the S1 state or an even higher excited state after UV exposure and molecules in S1 will cross a lower energy barrier to reach the conical intersection. The adiabatic trans-cis isomerization process happened and finally return to the ground. Meanwhile, FTAS clarified the time scale of trans-cis isomerization of two molecules was âˆ¼ 10 ps, which also met the requirement of fast energy relaxation. This work also provides theoretical guidance for developing new sunscreen molecules from natural stilbene.

A highly selective red-emitting fluorescent probe and its micro-nano-assembly for imaging endogenous peroxynitrite (ONOO-) in living cells.

Endogenous peroxynitrite plays a very important role in the regulation of life activities. However, validated tools for ONOO- tests are currently insufficient. We designed a fluorescent probe TPA-F-NO2 with a low fluorescence background in water based on the D-π-A structure for the imaging of endogenous ONOO- in living cells. TPA-F-NO2 can realize the naked eye detection of ONOO- due to the obvious color change. TPA-F-NO2 has the advantages of large stokes shift, high signal-to-noise ratio, high selectivity and sensitivity. The quantitative detection can be achieved in the range of 0-14 µM ONOO-. Due to its solvatochromic characteristics, TPA-F-NO2 has the potential to be used in OLEDs and other fields. In addition, 4-methylumbelliferone has a wide range of anticancer effects as an inhibitor of hyaluronic acid. We prepared TPA-MU-NPs by assembling TPA-F-NO2 and 4-methylumbelliferone. It also endows TPA-MU-NPs with ONOO- imaging function and anti-proliferation effect on breast cancer cells and other cells. This 'probe-drug' assembly strategy provides ideas for the design and optimization of dual-functional probes.

Cubic Halide Double Perovskite Nanocrystals with Anisotropic Free Excitons and Self-Trapped Exciton Photoluminescence.

In this work, we first developed Cs2KBiCl6 cubic double perovskite nanocrystals and a series of morphologically isotropic double perovskite nanocrystals. Different contributions of different elements to self-trapped states were revealed by density functional theory. Meanwhile, these double perovskite nanocrystals exhibit the coexistence of free and self-trapped exciton dual-color photoluminescence. Femtosecond transient absorption spectroscopy can confirm that the double perovskite nanocrystals produce a relatively obvious structural deformation in the excited state. We infer that this can lead to a large deviation of the excitation and emission transition dipoles, thus causing large photoluminescence anisotropy. Most importantly, we observe for the first time that both free exciton emission and self-trapped exciton emission are highly anisotropic, which are comparable to or even better than that of lead halide perovskites. This research paves the way for exploring more possibilities and practical applications.

Suppression of Energy Metabolism in Cancer Cells with Nutrient-Sensing Nanodrugs.

Uncontrolled growth of tumor cells is highly dependent on the energy metabolism. Fasting-mimicking diet (FMD) is a low-calorie, low-protein, low-sugar diet representing a promising strategy for cancer treatment. However, triglyceride stored in adipose tissue is hydrolyzed into free fatty acids and glycerol for energy supply during FMD treatment. Herein, we design a nutrient-sensing nanodrug, VFETX, which is self-assembled with vitamin B1 (VB1), ferrous ions, and etomoxir (ETX). FMD treatment upregulate the expression of VB1 transporters on tumor cells, thereby increasing cellular uptake and tumor accumulation of VFETX. Importantly, treatments of VFETX and FMD synergistically inhibit the energy metabolism in tumor cells and subsequently markedly enhance cytotoxicity of ETX. As a result, VFETX nanodrugs efficiently inhibit the growth of two tumor models in vivo without obvious side effects. This study demonstrates the potential of FMD-assisted nutrient-sensing nanodrugs for cancer therapy.

Efficient Photoluminescence of Manganese-Doped Two-Dimensional Chiral Alloyed Perovskites.

In this work, we introduced chiral cations into the achiral two-position layered perovskite system for the first time to form an alloyed system that still retains a clear layered structure. In addition, in order to explore the potential photoelectric properties of the alloyed system, manganese ions were doped into the alloyed system. The XRD pattern shows that the steady-state absorption and emission spectra of the alloyed system have a large structural distance, while the doped manganese system exhibits a two-color photoluminescence phenomenon. In addition, combined with time-resolved fluorescence and testing, the photoluminescence characteristics and ultralong lifetime of Mn-doped samples were further characterized. The exciton band structure of the lead halide perovskite framework can be adjusted through this design strategy. Mn2+ ions can form characteristic energy levels in the host system and then energy transfer of excitons occurs, which is of great significance for the development of new functional and high-efficiency photoluminescent materials.

Thermally Activated Delayed Fluorescence Enabled by Reversed Conformational Distortion for Blue Emitters.

In this work, we present for the first time a general strategy via molecular reversed conformational distortion for thermally activated delayed fluorescence (TADF). A model purely organic compound named BNNIO with a common fluorophore flexibly linked to benzene by an oxygen atom is rationally designed and successfully synthesized. Moreover, the rate constant of reverse intersystem crossing reaches 2.34 × 104 s-1 as determined by transient spectroscopy. As a result, TADF emission of BNNIO is observed with a photoluminescence quantum yield of 90.72% and a lifetime of 84.76 µs at 415 nm. This universal regulation strategy undoubtedly opens a new avenue for the development of novel purely organic blue light-emitting materials.

Nonadiabatic Dynamics Mechanism of Chalcone Analogue Sunscreen FPPO-HBr: Excited State Intramolecular Proton Transfer Followed by Conformation Twisting.

Nowadays, traditional sunscreen molecules face many adverse problems: single energy relaxation pathway, lack of adequate UVA light protection, and therefore no longer meeting the growing demand for UVA protection. In this work, we reported a novel sunscreen molecule (E)-3-(5-bromofuran-2-yl)-1-(2-hydroxyphenyl)prop-2-en-1-one (hereinafter referred to as FPPO-HBr) which tackled adverse problems of traditional sunscreen molecules as single energy relaxation pathway, lacking effective UVA light protection. Various nonradiative pathways were proposed and verified by combining the steady-state and femtosecond transient absorption (FTA) spectroscopy and theoretical calculation. Upon UV excitation, the FPPO-HBr mainly decays via excited-state intramolecular proton transfer (ESIPT) followed by conformation twist in ultrafast manner. Importantly, 1H NMR spectra proved that the FPPO-HBr could not undergo trans-cis photoisomerization. Additionally, excellent photostability was also observed for newly synthesized FPPO-HBr. The current work could provide new perspectives for sunscreen molecules synthesis and mechanism.

New insights into ESIPT mechanism of three sunscreen compounds in solution: A combined experimental and theoretical study.

In this present work, we have successfully designed and investigated three flavonoid sunscreen compounds. Based on steady-state spectroscopy and time-dependent density functional theory (TDDFT), the mechanism of excited state intramolecular proton transfer (ESIPT) of sunscreen compounds was studied. The calculated UV-vis absorption spectra and fluorescence emission spectra are in good agreement with the experimental results in methanol solution. The potential energy curve demonstrates that the ESIPT process can easily occur in the three sunscreen compounds without energy barrier. Therefore, the absorbed excitation energy can get back to the ground state through a non-radiative relaxation process. Light stability tests ensure that the three flavonoids have the potential as sunscreens. This work provides not only an application of the ESIPT process in sunscreen mechanisms, but also a theory basis for the development of novel sunscreen molecules.

Unveiling the nonadiabatic photoisomerization mechanism of hemicyanines for UV photoprotection.

In this work, the nonadiabatic energy relaxation mechanism of hemicyanines for UV photoprotection were investigated by using the density functional theory (DFT) and time-dependent density functional theory (TDDFT) method for the first time. The absorption spectra and potential energy surfaces (PESs) of four hemicyanines with different positions of substituents were presented. The maximum absorption peaks of the four hemicyanines are located in the UVA region. In addition, all these hemicyanine molecules also have light absorption in both the UVB and UVC regions. At the same time, we found that the trans-cis photoisomerization PESs of all these hemicyanines have a significant conical intersection (CI) point between the first excited state and the ground state. Herein, it was first demonstrated that the UV energy absorbed by the hemicyanines could be dissipated nonadiabatically through the CI point by using the trans-cis photoisomerization dynamics mechanism. This work proves that hemicyanines have the possibility to be applied for UV photoabsorbers, and provides important basis for designing new type of hemicyanines for UV photoprotection.

Inversing supramolecular chirality and boosting circularly polarized luminescence of pyrene moieties via a gel matrix.

Alkyl-substituted l/d-glutamide derivatives (L/D-SG) were designed as gelators to fabricate host gel matrices. Pyrene-appended l/d-glutamide derivatives (Py-LG/Py-DG) were employed as guest luminophores to investigate chiral packing and emission behavior in gel matrices. It was found that Py-LG and Py-DG are prone to form P- and M-chirally packed assemblies in DMSO gels, respectively. However, the chiral packing was inversed, and CPL was boosted after Py-LG/Py-DG was embedded in the L/D-SG gel matrix. M-chiral packing together with left-handed excimer emission ((-)-CPL) was observed in the Py-LG immobilized L-SG gel matrix, while P-chiral packing together with right-handed excimer emission ((+)-CPL) was found in the Py-DG immobilized L-SG gel matrix. It is more interesting to find that the molecular chirality of the matrix gelator did not affect the supramolecular chirality of pyrene assemblies. Either l or a d-matrix gelator can inverse the supramolecular chirality of the pure gel, but did not follow the chirality of the matrix. It was found that the gel matrix converts intralayer pyrene-pyrene (Py-Py) packing in the pure pyrene gel to interlayer Py-Py packing, thus giving an opposite chirality. The study not only deepened our understanding of the supramolecular chirality transfer but also unveiled the effects of an inert gel matrix in regulating the chiroptical properties.

Unveiling the photoluminescence regulation of colloidal perovskite quantum dots via defect passivation and lattice distortion by potassium cations doping: Not the more the better.

In this work, we have first demonstrated that the potassium cation doping effect on photoluminescence (PL) regulation of CH3NH3PbBr3 (CH3NH3+=MA+) colloidal perovskite quantum dots (QDs) is significantly different from the other alkali cation doping effects. The PL intensity will be generally enhanced with the increase doping amounts of other alkali cations. Herein, we have unveiled that the PL of the potassium-doped perovskite QDs is initially prompted by the potassium ions doping and then inhibited with further growing doping amount of the potassium ions. Furthermore, we have also demonstrated that the PL inhibition phenomenon is ascribed as quick trapping of redundant photogenerated electrons by the trap states after huge amount doping besides defect passivation and octahedral structure distortion induced by the initial doping. At the same time, the specific excited state transient absorption and the lifetime of MAxK1-xPbBr3 also confirm that the radiation recombination process is enhanced via defect passivation and lattice distortion, which is induced by moderate potassium cations doping. In addition, the PL of colloidal perovskite quantum dots can be adjusted from orange to cyan within the wavelength range of 300 nm - 600 nm and exhibit better stability.

Excited state electronic structures and photochemistry of different oxidation states of 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS).

The molecular structures of 2,2-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), were calculated by using time-dependent density functional theory (TDDFT) model with M062X method with 6-311G (d, p) basis set. In this work, the ABTS were theoretically investigated from the geometric structure, the energy levels of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), the energy level gap ΔEHOMO-LUMO of the molecular ground state, excited stated properties and the electronic absorption spectra of different oxidation states. We studied the energy levels of LUMO and HOMO of ABTS in different oxidation states. Frontier molecular orbital analysis can provide insight into the nature of excited states. ABTS was synthesized from N-ethylamine by total synthesis. Then, we measured the UV-Vis spectra of ABTS before and after being oxidized by K2S2O8. The calculated electronic structures and photochemical properties of different oxidation state of ABTS were in accordance with the experimental result. This work demonstrates the relationship between the electronic structures and photochemistry of different oxidation states ABTS hence paves the way for the rationally synthesis and deepen understanding of the photophysical properties of ABTS materials.

Excitons competition regulation via organic cation-site and halogen-site co-halogenation of (X-p-PEA)2Pb(Cl/Br)4 perovskites.

In this work, we report a family of co-halogenated two-dimensional hybrid perovskites (2DHPs) based on phenethylammonium lead halogen ((PEA)2Pb(Cl/Br)4) in which the organic cation-site (PEA) is substituted with halogen at the para-site, namely the formation of 4-halophenethylamine (X-p-PEA) (X = Cl, Br; p: para-site). The organic cations are regulated by introducing halogen ions at the para-site of the benzene ring to promote the structural distortion of the lead halide octahedral inorganic layer. Furthermore, (X-p-PEA) causes a shift in the energy band distribution of 2DHPs. In this case, the photoluminescence competition of free excitons (FEs) and self-trapped excitons (STEs) changes the microscopic relaxation process of excitons. In addition, we found that (Br-p-PEA) can increase the photoluminescence quantum yield (PLQY). At the same time, we regulate the halogen-site of perovskites from lead-chloride perovskites (LCPs) to lead bromine perovskites (LBPs), achieving emission from white light to blue light. Therefore, the co-halogenation regulation strategy of organic cation-site and halogen-site can effectively regulate the photoluminescence wavelength and improve the PLQY. This is of great significance for the development of perovskite materials with specific optoelectronic applications.

Circularly Polarized Luminescence from Solvent-Free Chiral Organic π-Liquids.

The solvent-free organic π-liquids have been attracting increasing attentions owing to the inherent optoelectronic properties accompanied by the advantages of non-volatility and high processability. Herein, we reported a series of naphthalene derivatives substituted with chiral branched alkyl chains, which are present as liquids (Nap1-3) or solid (Nap4) at room temperature, depending on the substitution positions. Circular dichroism (CD) and circularly polarized luminescence (CPL) were only observed for enantiomeric Nap2 (2,3-substituted) liquid. It is suggested that the chiral aggregation in the π-liquid leads to the CD signal and the chiral excimer resulting in the CPL performance. When achiral anthracene or pyrene was dissolved in Nap2, the π-liquid could serve as chirality and energy transfer media in which both CD and CPL emerged from the achiral anthracene. A CPL dissymmetry factor (|glum |) of anthracene reached to 5.2×10-2 when dissolved in chiral Nap2 liquid, which is nearly two orders of magnitude higher than that of the pure Nap2 π-liquid.

Codoping of Lead-Free Double Perovskites Promotes Near-Infrared Photoluminescence.

In the rapidly developing smart era, near-infrared luminescent materials have important applications in various fields that are closely related to people. Nag and co-workers provided a first codoping strategy to achieve efficient near-infrared photoluminescence in lead-free double perovskite materials. Through the introduction of Bi3+ ions, a new energy state is formed that leads to the absorption of lower-energy light. The excited state formed by this light absorption subsequently excites f-electrons of Er3+ or Yb3+ ions, and the relaxation of these f-electrons results in near-infrared photoluminescence. This may open a new chapter in the application of perovskites for infrared detection and human sensing.