Mechano‐fluorochromic PtII Luminogen and Its Cysteine Recognition

A new triphenylamine‐based organometallic Pt^II luminogen ( 1 ) and its analogous organic compound ( 2 ) are reported. The molecules are decorated with aldehyde functionality to improve their photophysical properties by utilising donor–acceptor interactions. The single crystal X‐ray structure analysis of Pt^II analogue 1 revealed that the neighbouring molecules were loosely organised by weak intermolecular C?H???π interactions. Because of the twisted nature of the triphenylamine backbone the compounds showed aggregation‐induced emission enhancement in THF/water mixture. Due to their loose crystal packing, upon application of external stimuli these luminogens exhibited mechano‐fluorochromic behaviour. The crystalline forms of the compounds displayed a more superior emission efficiency than the grinded samples. Moreover, the compounds showed crystallization‐induced emission enhancement (CIEE) and exhibited chemodosimetric response towards cysteine under physiological condition.     

Synthesis of new tripodal receptors—a ‘PET’ based ‘off-on’ recognition of Ag

A new set of tripodal receptors based upon an aromatic platform have been synthesized in high yields. The compounds have been characterized by spectroscopic techniques and by single crystal X-ray crystallography. These receptors are found to have good extraction ability and high transport rate for Ag(I). The receptor with imine linkages exhibits weak fluorescence emission bands at λ_max=413 and 540 nm, upon excitation at λ_max=365 nm. The fluorescence spectrum of the receptor shows enhancement in the intensity of the signal at 413 nm on binding with the Ag⁺ cation. No such significant changes are observed with other metal ions. An absorption at ∼365 nm is typical of an intraligand (π-π^∗) transition involving the imine chromophore, which produces a weak emission band at 413 nm due to quenching caused by PET from a neighboring -OH group. Participation of OH group in coordination to the metal ion reduces PET and an enhancement of fluorescence intensity is observed, signaling recognition of the metal ion.     

Photophysical properties of phenanthro[9,10-d]imidazole-type fluorescent hosts upon inclusion of organic solvent molecules

The crystal of phenanthro[9,10-d]imidazole-type fluorescent clathrate host (1) exhibits fluorescence enhancement behavior with a blue-shift of the emission maximum upon enclathration of organic solvent molecules such as 1-butanol and morpholine, whereas the crystal of 1 exhibits fluorescence enhancement behavior with a red-shift of the emission maximum upon enclathration of carboxylic acid such as acetic acid and propionic acid. The crystal structures of the guest-free and the guest-inclusion compounds of 1 have been determined by X-ray analysis. On the bases of the spectral data and the crystal structures, the effects of the enclathrated guest molecule on the solid-state photophysical properties of the guest-inclusion compounds are discussed.     

Theoretical study on the second-order nonlinear optical properties and reorganization energy of silafluorenes and spirobisilafluorenes derivatives

The electronic absorption and emission spectra, second-order polarizability and reorganization energy of the twenty silafluorenes and spirobisilafluorenes derivatives have been studied at the density functional theory level. The results show that the second-order polarizability (β) increases with increase in the number of the branches due to cooperative enhancement of the charge transfer, whereas the reorganization energy (λ) follows the opposite trend for the studied compounds. The properties (β and λ) of the compounds at the 3, 6-positions substitution are much better than those of compounds at the 2, 7-positions substitution. The effects of donor/acceptor (D/A) substitution and different spiroatoms (silicon or carbon) on second-order polarizability and reorganization energy are also discussed. It is noted that the charge transport properties can be tuned by changing the donor/acceptor (D/A) substitution, and the acceptor substitution can greatly reduce the reorganization energy. The electronic absorption spectra show that all studied compounds can meet the requirement of nonlinear optical (NLO) transparency. Thus, increasing the number of branches and acceptor substitution can remarkably enhance performance of this kind of compounds. Based on larger β, smaller λ and excellent optical transparency, this kind of compounds have a possibility to be excellent second-order NLO or charge transport materials.     

Boron Diiminate with Aggregation‐Induced Emission and Crystallization‐Induced Emission‐Enhancement Characteristics

Organoboron complexes having aggregation‐ and crystalization‐induced emission properties are presented. The series of boron diiminates were synthesized and the emission behaviors of the synthesized compounds were investigated. Finally, it was found that significant enhancement of the emission depended on the crystallinity in the solid states.     

Enhanced photoluminescence from group 14 metalloles in aggregated and solid solutions

The unusual photoluminescence characteristics of a series of six group 14 metalloles (1,1-dimethyl-2,3,4,5-tetraphenylmetalloles and 1,1-diphenyl-2,3,4,5-tetraphenylmetalloles) containing silicon, germanium, or tin have been investigated. Although the compounds are weakly luminescent in dilute fluid solution at room temperature, they undergo a substantial enhancement of photoluminescence when forced to aggregate, as in mixed solvent systems. The compounds also exhibit considerable emission when incorporated into rigid room-temperature glasses of sucrose octaacetate. Absorption and emission characteristics of the compounds, including luminescence quantum yields, in fluid solution, solution-phase aggregates, and room-temperature glasses are reported. Quantum yields increase by as much as 2 orders of magnitude in the aggregates and glasses, compared to fluid solution. Experimental evidence supports the conclusion that the aggregation-induced enhancement of luminescence results from restricted intramolecular rotations in the packed metalloles. The unusual aggregation-induced enhancement of these compounds makes them potentially useful for the fabrication of a variety of electrooptical devices and sensors. In addition, the X-ray crystal structure of hexaphenylgermole is reported.     

Effect of a perfluorocyclopentene core unit on the structures and photoluminescence of fluorene- and anthracene-based compounds

A novel series of blue luminescent compounds, in which three identical functional groups, such as fluorene, anthracene, and spiro-bifluorene, are linked distortedly around a perfluorocyclopentene core, have been synthesized and characterized. The introduction of a perfluorocyclopentene linkage into the molecular framework leads to an enhancement of the photoluminescence (PL) efficiency and thermal stability. All compounds exhibit intense blue photoluminescence, which has been attributed to fluorene- or anthracene-based π→π* transitions. The maximum emission wavelengths of all compounds at room temperature are in the region of 420-480 nm, with higher PL quantum efficiencies than in 9,10-diphenylanthracene. The electroluminescent (EL) properties of compound 4, 1,2-bis(9,9′-spirobifluoren-2-yl)-3,3,4,4,5,5-hexafluorocyclopentene, were investigated. A multilayer EL device with the configuration of ITO/2TNATA(60 nm)/NPB(20 nm)/ADN:2%-compound-4(35 nm)/Alq₃(20 nm)/LiF(2 nm)/Al has been successfully fabricated.     

Emission enhancement using two orthogonal targets in double pulse laser-induced breakdown spectroscopy

The enhancement of emission intensity resulting from the interaction between two laser-induced plasmas on two orthogonal targets was investigated using double pulse laser-induced breakdown spectroscopy (LIBS) at 0.7 Pa, by means of time-resolved spectroscopy and fast photography. The results showed that the interaction between both plasmas improved carbon emission intensity in comparison to a single laser-induced plasma. For all the carbon lines of interest 477.2 nm (CI), 426.7 nm (CII), and 473.4 nm (C₂ Swan band head), the intensity enhancement showed a maximum at a delay between lasers in the range from 2 to 5 μs; moreover it increased with the fluence of the first laser. On the other hand, in the case of C₂ the intensity enhancement reached a maximum at 5 mm from the target; however it decreased with increasing fluence of the second laser. The largest intensity enhancement found was twofold for atomic species and sixfold for molecular species.     

5,6-位烷氧基保护和3-/3,8-位三苯胺拓展1,10-菲咯啉衍生物与银离子识别

在1,10-菲咯啉的5,6-位引入烷氧基后,分子的反应活性明显提升,同时获得的三苯胺基(TPA)衍生物的溶解性也明显提高。晶体结构分析表明:烷氧基团是以六元环形式的乙撑二氧结构接入1,10-菲咯啉环的5,6-位。化合物TPA1和TPA2均对Ag+表现出选择性识别作用。其中,TPA1与Ag+作用后虽然荧光减弱不明显,但其发射波长明显红移(47 nm)。而TPA2和Ag+作用后,415和542 nm处荧光发射峰同时淬灭。化合物TPA3虽然也能与Ag+发生相互作用使荧光减弱,但是其荧光减弱幅度不大,很容易受到其它杂离子干扰影响,不适用于离子识别研究。     

Aggregation‐Induced Emission and Sensing Characteristics of Triarylborane–Oligothiophene–Dicyanovinyl Triads

The design, synthesis and aggregation‐induced emission properties of a new series of triarylborane–oligothiophene–dicyanovinyl (DCV) conjugates 4 – 6 (A–D–A’ type molecular configuration) are reported. The optical properties of 4 – 6 can be modulated by judiciously varying the number of thiophene units between electron deficient boryl and dicyanovinyl units. Compound 6 with terthiophene spacer showed highly red‐shifted absorption and emission compared to 5 and 4 with bithiophene and monothiophene spacers, respectively. Compounds 5 and 6 show aggregation‐induced emission enhancement in water/THF mixtures. Compounds 5 and 6 also showed solvent viscosity dependent emission characteristics. All the three compounds show distinct optical responses for small anions such as fluoride and cyanide. Filter paper strips coated with compounds 5 and 6 can detect F^? and CN^? in aqueous media with different colorimetric responses.     

Pressure‐Induced Emission Enhancement of a Series of Dicyanovinyl‐Substituted Aromatics: Pressure Tuning of the Molecular Population with Different Conformations

A series of dicyanovinyl‐substituted aromatic compounds (Ar‐DCV; Ar=9‐anthracenyl, 1‐naphthyl, 1‐pyrenyl) with dual fluorescence are prepared, and their emission properties—when molecularly dispersed in a polymer medium—are investigated under pressure perturbation. The total emission intensity is enhanced drastically from ambient pressure up to 70 kbar. Emission 30–107 times more intense than that at ambient pressure is observed at higher pressure. In dual emission, the enhancement of the local excited state (LE state) is significantly different from that of the intramolecular charge‐transfer state (ICT state). The intensity of the ICT emission increases faster (30–370 times) than that of the LE emission (less than 20 times). In accordance with spectroscopic data, emission dynamics at different pressures, and computational studies on the molecular conformations of these compounds, a kinetic model is proposed to explain the effect of pressure on the emissive properties of the Ar‐DCV compounds from the point of view of pressure‐dependent populations of the species in the ground state.     

Controlled emission enhancement and quenching by self-assembly of low molecular weight thiophene derivatives

Three thiophene-containing compounds were newly synthesized as low molecular weight blocks to construct non-covalent and highly ordered π-conjugation systems. Typical emission enhancement and quenching based on the J- and H-type orientations, respectively, of the thiophene moiety were realized and controlled by lipid membrane-like phase transition and separation behaviours.     

Enhancement of electroluminescence intensity in poly(3-alkylthiophene) with different alkyl side-chain length by doping of fluorescent dye

Electroluminescent diodes utilizing poly(3-alkylthiophene) (PAT) containing fluorescent dyes have been fabricated and their unique enhancement of emission characteristics have been studied. Remarkable enhancement of the electroluminescence efficiency has been observed for diodes with PAT doped with oxadiazole derivative (2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole; PBD) and perylene derivative (N,N′ - Bis(2,5 - di - tert - butylphenyl) - 3,4,9,10 - perylenedi- carboximide; BPPC). The mechanism of emission enhancement by doping of PBD into PAT has been discussed with different alkyl side-chain lengths. © 1997 John Wiley & Sons, Ltd.     

Benzosiloles with Crystallization-Induced Emission Enhancement of Electrochemiluminescence: Synthesis,Electrochemistry, and Crystallography

Crystallization-induced emission enhancement (CIEE) was demonstrated for the first time for electrochemilunimescence (ECL) with two new benzosiloles. Compared with their solution, the films of the two benzosiloles gave CIEE of 24 and 16 times. The mechanism of the CIEE-ECL was examined by spooling ECL spectroscopy, X-ray crystal structure analysis, photoluminescence, and DFT calculations. This CIEE-ECL system is a complement to the well-established aggregation-induced emission enhancement (AIEE) systems. Unique intermolecular interactions are noted in the crystalline chromophore. The first heterogeneous ECL system is established for organic compounds with highly hydrophobic properties.     

Unsymmetrical photochromic bithienylethene-bridge tetraphenylethene molecular switches: Synthesis,aggregation-induced emission and information storage

Aggregation-induced emission(AIE) active photochromic molecules have attracted growing attention for their versatile applications.Here we designed and synthesized five newly unsymmetrical photochromic diarylethene(DAE) dyads(BTE1-5) by connecting tetraphenylethene(TPE) and aromatic substituent via bithienylethene(BTE) bridge.The chemical structures of those compounds were identified by ^1H NMR,¹³C NMR and HRMS.The absorption and emission of these dyads were investigated by UV-vis and fluore scence spectroscopy,respectively.The results showed that all those compounds exhibited typically AIE or aggregation-induced emission enhancement(AIEE) characteristic.Particularly,when an aggregationcaused quenching(ACQ) fluorophore(triphenylamine) was grafted to the molecule,connecting with TPE via BTE-bridge,the ACQ phenomenon was dissipated and converted to an AIE luminophore,and those compounds exhibited photochromism upon irradiation with alternative UV and visible light.The solution or solid of those compounds showed distinctly fluorescence switching "ON" or "OFF" observation upon irradiation with alternative UV and visible light.It is interesting that BTE1 could be applied in recording and rewritable information storage,and the cyclization quantum yields could be affected by substituent significantly.     

Optical emission studies of plasma induced by single and double femtosecond laser pulses

Double-pulse femtosecond laser ablation has been shown to lead to significant increase of the intensity and reproducibility of the optical emission signal compared to single-pulse ablation particularly when an appropriate interpulse delay is selected, that is typically in the range of 50–1000 ps. This effect can be especially advantageous in the context of femtosecond laser-induced breakdown spectroscopy analysis of materials. A detailed comparative study of collinear double- over single-pulse femtosecond laser-induced breakdown spectroscopy has been carried out, based on measurements of emission lifetime, temperature and electronic density of plasmas, produced during laser ablation of brass with 450 fs laser pulses at 248 nm. The results obtained show a distinct increase of plasma temperature and electronic density as well as a longer decay time in the double-pulse case. The plasma temperature increase is in agreement with the observed dependence of the emission intensity enhancement on the upper energy level of the corresponding spectral line. Namely, intensity enhancement of emission lines originating from higher lying levels is more profound compared to that of lines arising from lower energy levels. Finally, a substantial decrease of the plasma threshold fluence was observed in the double-pulse arrangement; this enables sensitive analysis with minimal damage on the sample surface.     

Synthesis and Fluorescent Properties of Tetra‐Biphenyl N‐Substituted Phthalimides

A series of tetra(biphenyl‐4‐yl)phthalimide (TBPPI ) derivatives with different N‐substituents (n‐butyl, phenyl, p‐methyl phenyl, and p‐acetyl phenyl moieties for compounds 7 – 10 , respectively) were prepared to examine their fluorescent behavior under various conditions. The chemical structure of compound 7 has been successfully confirmed by single crystal X‐ray diffraction analysis. The photoluminescence (PL ) spectra in different ratios of CH ₂Cl ₂/EtOH mixture solutions revealed that compounds 7 and 8 exhibited both aggregation‐induced emission (AIE ) and aggregation‐caused quenching (ACQ ) behaviors, while compounds 9 and 10 displayed AIE and aggregation‐induced emission enhancement (AIEE ) properties, respectively.     

5,6-位烷氧基保护和3-/3,8-位三苯胺拓展1,10-菲咯啉衍生物与银离子识别

在1,10-菲咯啉的5,6-位引入烷氧基后,分子的反应活性明显提升,同时获得的三苯胺基（TPA）衍生物的溶解性也明显提高。晶体结构分析表明：烷氧基团是以六元环形式的乙撑二氧结构接入1,10-菲咯啉环的5,6-位。化合物TPA1和TPA2均对Ag+表现出选择性识别作用。其中,TPA1与Ag⁺作用后虽然荧光减弱不明显,但其发射波长明显红移（47 nm）。而TPA2和Ag⁺作用后,415和542 nm处荧光发射峰同时淬灭。化合物TPA3虽然也能与Ag⁺发生相互作用使荧光减弱,但是其荧光减弱幅度不大,很容易受到其它杂离子干扰影响,不适用于离子识别研究。     

Borylated Arylisoquinolines: Photophysical Properties and Switching Behavior of Promising Tunable Fluorophores

A series of nine borylated arylisoquinolines has been prepared with systematic variation in their electronic properties and their photophysical properties were investigated. The color of their fluorescence can be finely tuned by changing the properties of the aryl moiety, which is involved in internal‐charge‐transfer processes. For example, methoxy‐substituted compound 5 showed an intense green emission, whereas dimethylamino‐substituted compound 6 showed an orange‐red emission. These new fluorophores were tested for their potential as molecular switches with external ionic stimuli, such as protons and fluoride ions. On the one hand, protonation of the isoquinoline moiety led to fluorescence enhancement for compounds that showed weak charge transfer and fluorescence quenching for compounds that showed strong charge transfer. On the other hand, the formation of ate complexes with fluoride led to strong fluorescence quenching in all of the investigated cases.     

Study of the fluorescent properties of partially hydrogenated 1,1'-bi-2-naphthol-amine molecules and their use for enantioselective fluorescent recognition

The fluorescent properties of a series of H(8)BINOL-amine compounds are investigated. It is revealed that the intramolecular hydrogen bonds of these compounds contribute to the shift of the emission of their H(8)BINOL unit to a much longer wavelength. That is, the emission of H(8)BINOL is at λ = 323 nm, but that of the H(8)BINOL-amino alcohol (S)-5 is at λ = 390 nm. Binding of (S)-5 with mandelic acid suppresses its intramolecular hydrogen bonding and restores the short wavelength emission of the H(8)BINOL unit. When (S)-5 (1.0 × 10(-4) in CH(2)Cl(2)) was treated with (R)-mandelic acid (4.0 × 10(-3)), a large fluorescence enhancement at the short wavelength (λ(emi) = 330 nm) was observed with I(R)/I(0) = 11.7. When (S)-MA was used under the same conditions, the enhancement at the short wavelength emission was much smaller. Thus, a good enantioselective fluorescent response was observed with ef =3.5 [ef: enantioselective fluorescence enhancement ratio = (I(R) - I(0))/(I(S) - I(0))]. This study demonstrates that the H(8)BINOL-based molecules are promising as a new class of enantioselective fluorescent sensors.