•A new ratiometric chemodosimeter for Hg2+ and Fe3+ is synthesized.•REPN exhibits a typical FRET behavior to Hg2+.•REPN performed ratiometric detection for Fe3+.•The nanoparticles maintained the AIE effect with higher water solubility.A novel ratiometric fluorescent chemodosimeter REPN based on 1,8-naphthalimide-rhodamine was successfully synthesized. Two different strategies of fluorescence resonance energy transfer (FRET) and photo-induced electron transfer (PET) for ratiometric detection of Hg2+/Fe3+ were designed into one sensing system. REPN exhibits typical FRET signal from pyridine-naphthalimide moiety to rhodamine moiety which was induced by Hg2+ with a detection limit of 2.72 × 10−6 M in EtOH/PBS buffer (1:1, v/v, pH = 7.4) solution. However, the probe REPN performed ratiometric detection behavior via PET process combined with the classical ring-opening sensor system in the presence of Fe3+, the detection limit was 5.7 × 10−7 M. REPN emitted bright yellow fluorescence in solid state and the maximum emission wavelength was 538 nm. Besides, the silica nanoparticles loaded AIE dye REPN maintained and further reinforced the AIE effect with higher water solubility.

•Two novel intramolecular fluorescence resonance energy transfer (FRET) dendritic sensors have been synthesized.•Cu(I)-catalyzed click reactions between terminal alkynes and azides is used.•The BODIPY sensor is high sensitive and good selective to Hg(II).Two novel intramolecular fluorescence resonance energy transfer (FRET) dendritic compounds RhB-BODIPY and NPI-BODIPY have been synthesized utilizing click reaction and characterized. The fluorescence intensity of RhB-BODIPY at 580 nm was amplified with 10.7-fold on addition of Hg2+ and the fluorescence resonance energy transfer efficiency between the energy donor (BODIPY) and the energy acceptor (rhodamine) is 67%. In compound NPI-BODIPY, the naphthalimide serves as donor and BODIPY serves as acceptor. The energy transfer efficiency of NPI-BODIPY is 72%. The comparative sensing abilities of RhB-BODIPY toward a range of metal ions have been investigated and it exhibited appreciable selectivity towards Hg2+. Job’s plot clearly indicated that the binding ratio of RhB-BODIPY with Hg2+ is 1:2. The 1H NMR titration of RhB-BODIPY with Hg2+ confirmed that tertiary amines and triazoles were involved in the binding event. The detection limit estimated from the titration results were 3.34 × 10−7 M for RhB-BODIPY. The fluorescence quantum yield of RhB-BODIPY and NPI-BODIPY at 510 nm were 53% and 88% respectively. In addition, both two compounds were successfully applied to living cell imaging.In presence of Hg2+ ions, the fluorescence intensity at band 580 nm enhanced significantly, which is attribute to the spirolactam ring opened of the rhodamine unit. Then the energy was transferred from BODIPY to rhodamine with the energy transfer efficiency is 67%. The binding ratio of RhB-BODIPY with Hg2+ is 1:2.

Hypochlorite serves as a significant antimicrobial agent in the human immune system, and its detection is of great importance. Herein, a novel near-infrared BODIPY-based ClO− fluorescent probe (NCS-BOD-OCH3) was designed and synthesized. The emission bands of NCS-BOD-OCH3 concentrated at 595 nm and 665 nm. Since the electron withdrawing group 1,3,4-oxadiazole was formed after the desulfurization reaction, the fluorescence intensity of NCS-BOD-OCH3 decreased significantly in THF/H2O (v/v, 1 : 1, buffered with 10 mM PBS pH = 7.4), which is visible to the naked eye with an obvious color change. NCS-BOD-OCH3 can realize the two-photon up-converted fluorescence emission. The low detection limit was calculated from the titration results, with the figure for NCS-BOD-OCH3/ClO− being 1.15 × 10−6 M. The result of living cell imaging experiment demonstrated that NCS-BOD-OCH3 can successfully detect ClO− in living cells and can serve as a NIR mitochondrial imaging agent. It is an excellent platform for developing NIR ClO− fluorescent probes.

Herein, a colorimetric and ratiometric probe, BCPA–BODIPY–TCF, for hypochlorite (ClO−) based on a D–π–A structure was synthesized through the Knoevenagel reaction, which consisted of donating groups (3,6-di-tert-butylcarbazol-9-yl)triphenylamine–BODIPY conjugated with a strong electronic acceptor group, 2-dicyanomethylene-4,5,5-trimethyl-3-cyano-2,5-dihydrofuran (tricyanofuran). Upon the addition of ClO−, the probe displayed rapid identification, immediately accompanied with color change from purple to pink in one minute; this was attributed to the oxidative cleavage of an alkene linker between BODIPY and tricyanofuran. The introduction of tricyanofuran at the 2-position of BODIPY through a CC double bond made the absorption peak red-shift by 85 nm as compared to that of the precursor BCPA–BODIPY due to a strong intramolecular charge transfer (ICT) transition. Upon the addition of ClO−, the absorption peak at 580 nm gradually decreased, and the absorption band centred at 500 nm concomitantly increased. The probe was highly selective for ClO− detection without the interference of other anions and ROS. Additionally, a paper-based test strip was prepared and used as a naked-eye indicator for the presence of hypochlorite in practical tap water samples.

In this work, a novel pyridylvinyl rhodamine-naphthalimide ratiometric fluorescent probe, In this work, a novel pyridylvinyl rhodamine-naphthalimide ratiometric fluorescent probe, RNVP, was synthesized and characterized by 1H NMR, 13C NMR and HRMS techniques. This probe shows high selectivity and sensitivity towards Fe3+ and Hg2+. At a low concentration of Fe3+/Hg2+, a new emission peak appeared at 581 nm and enhanced significantly along with naked-eye sensitive color changes, which spirolactam-ring moiety of rhodamine was converted to the open-ring form in the presence of Fe3+/Hg2+. Further addition of Fe3+/Hg2+, the fluorescence intensity at 438 nm was enhanced rapidly, which attributed to the suppression of the PET process. The proposed sensing system of probe RNVP represented dual-channel and segment detection behavior, with the fluorescence “turn-On or Off” response and a very low detection limit of 2.72×10−8 M and 9.08×10−8 M, and the dissociation constant (Kd) were calculated to be 4.95×10−7 M3/2 and 6.68×10−8 M3/2, respectively. RNVP also quick responded linearly to the acidic solution and monitor the pH change in the range of 2.92–4.5, as well as excellent reversibility.Naked-eye visible and ratiometric chemodosimeter for Hg2+/Fe3+.Download high-res image (228KB)Download full-size image

•Two novel red BODIPY-Triphenylamine with conjugated pyridines and one quaternary pyridium salt were synthesized.•The long wavelength peaks of POPA-BODIPY, PPPA-BODIPY and PPSPA-BODIPY were located at 643 nm, 631 nm, 624 nm and the quantum yield of them was 0.16, 0.05, 0.10, respectively.•The detection limit of POPA-BODIPY, PPPA-BODIPY and PPSPA-BODIPY for BSA was calculated to be 1.44 × 10−7 M, 1.52 × 10−7 M, 5.37 × 10−8 M,respectively.•POPA-BODIPY was applied to cell imaging and showed a good uptake by SK-BR-3 cells.Two novel red BODIPY-Triphenylamine with conjugated pyridines and one quaternary pyridium salt were synthesized. The long wavelength peaks of POPA-BODIPY and PPPA-BODIPY which were located at 643 nm, 631 nm were predominant and the quantum yield of them was 0.16, 0.05, respectively, so both of them showed red fluorescence in THF. PPSPA-BODIPY had a red emission peak at 624 nm and the quantum yield was 0.10. All the three compounds exhibited good aggregation-induced emission property. Furthermore, the fluorescence intensity of these dyes was strengthened continuously with increasing concentration of bovine serum albumin (BSA) which showed that these dyes could be used as BSA probes. Meanwhile, the detection limit of POPA-BODIPY, PPPA-BODIPY and PPSPA-BODIPY for BSA was calculated to be 1.44 × 10−7 M, 1.52 × 10−7 M, 5.37 × 10−8 M,respectively. POPA-BODIPY was applied to cell imaging and showed a good uptake by SK-BR-3 cells which suggested its promising application for biosensors.Download high-res image (155KB)Download full-size image

A smart two-photon fluorescent platform based on desulfurization–cyclization was developed by attaching rhodamine to a cyanine skeleton through the Knoevenagel reaction. Based on the platform, a CyRSN probe was rationally designed and synthesized, in which morpholinyl naphthalimide and modified rhodamine thiohydrazide were linked to form a structure of monothio-bishydrazide. The probe exhibits excellent two-photon properties toward Hg2+ under Ti:sapphire pulsed laser 800 nm irradiation, allowing the naked-eye signal and fluorescence “turn-on” signal at 746 nm to be obviously distinguished. The addition of Hg2+ to the probe ensured that the naphthalimide donor and modified rhodamine acceptor were connected with electronically conjugated bonds (1,2,4-oxadiazole). Hence, a typical TBET process took place, resulting in an increase of the modified rhodamine NIR emission at 746 nm by about 34-fold as well as a decrease of the naphthalimide emission at 540 nm and producing a colorimetric change from pale yellow to green. The chemodosimeter exhibits a stable response for Hg2+ over other metal ions with a detection limit of 1.91 × 10−7 M, high sensitivity, a rapid response time, and pH independence under neutral conditions (pH 6.0–10.0). In addition, the CyRSN probe was successfully applied in the detection and quantification of Hg2+ in water samples with satisfactory recovery results.

In this work, two novel diarylanthracene conjugated dyes, CzAn and BCzAn, which contain carbazolyl substituted triarylamine groups, were synthesized by the Ullmann reaction and characterized by 1H NMR, 13C NMR, and HRMS-MALDI-TOF. Both of the diarylanthracene conjugated dyes CzAn and BCzAn demonstrated aggregation-induced emission enhancement (AIEE) properties. CzAn and BCzAn emitted brightly in solid states with maximum emission wavelengths of 576 and 601 nm. BCzAn emitted weakly in THF solutions with a fluorescence quantum yield of 8%, became a strong emitter in the aggregate states with the fluorescence peak intensity increased in THF–water mixtures and DMF–glycerol mixtures rather than in pure solvents. Nanoparticles (Nps) were prepared from CzAn and BCzAn by a hydrophobic interaction with bovine serum albumin (BSA). The diameters of the AIEE dye based BSA nanoparticles were characterized by transmission electron microscopy (TEM) and their photophysical properties were also measured. These BSA nanoparticles showed high water dispersibility, stable uniform morphology (100–200 nm), strong fluorescence, low cytotoxicity and excellent biocompatibility, making them good optical materials for living HeLa cell imaging.

A novel red aggregation-induced emission enhancement (AIEE) chromophore named BCPA–BODIPY was synthesized based on the construction units 4-N,N-bis[4-(3,6-di-tert-butylcarbazol-9-yl)phenyl]amino-benzaldehyde (BCPA) and fluorogen dipyrromethene boron difluoride (BODIPY). BCPA exhibits bright blue fluorescence (λem = 485 nm) in the solid state while BCPA–BODIPY emits bright red fluorescence in the solid state with a maximum emission wavelength at 633 nm. An obvious bathochromic shift from 485 nm to 633 nm was observed by modification of the BODIPY moiety on BCPA. Its fluorescence spectrum indicates that BCPA–BODIPY is a bimodal structure centred at 520 nm and 656 nm in THF solution; there was almost no fluorescence in pure THF. However, the intensities (>600 nm) increased obviously with much higher water fractions, demonstrating typical red fluorescence enhancement. Meanwhile, BCPA–BODIPY became a strong emitter in DMF and high viscosity glycerol mixtures which indicates that the intramolecular vibration and rotation of BCPA–BODIPY is considerably restricted in nanoaggregates formed in glycerol, thus leading to significant fluorescence enhancement. Besides, dye-loaded nanoparticles encapsulating BCPA–BODIPY maintain and further reinforce the AIEE effect and achieve higher water solubility. The pure dye was applied in cell imaging and showed a good uptake by MCF-7 cells which suggests it to be promising in biosensor applications.

•Two novel fluorescent compounds were synthesized based on pyridyltriphenylamine building block.•Probe PTRh can selectively recognize Hg2+ based on fluorescence resonance energy transfer (FRET).•Dye PTO was sucessfully encapsulated in silica nanoparticles and emitted bright blue fluorescence.•Both probe PTRh and PTO-doped silica nanoparticles could be successfully used as biosensors when uptaken by living cells.A novel pyridyltriphenylamine-rhodamine dye PTRh and a pyridyltriphenylamine derivative PTO were synthesized and characterized by 1H NMR and HRMS-MALDI-TOF. PTRh performed typical fluorescence resonance energy transfer (FRET) signal from pyridyltriphenylamine to rhodamine along with notable color change from green to rose when interacting with Hg2+ in EtOH/H2O. And PTRh as a ratiometric probe for Hg2+ based on FRET could achieve a very low detection limit of 32 nM and energy transfer efficiency of 83.7% in aqueous organic system. On the other hand, spectra properties of PTO in its aggregates, THF/H2O mixed solution and silica nanoparticles (Si-NPs) dispersed in water were investigated. And the results indicated PTO exhibited bright green fluorescence in solid state, and PTO was successfully encapsulated in silica matrix (30–40 nm), emitting bright blue fluorescence with 11.7% quantum yield. Additionally, living cell imaging experiments demonstrated that PTRh could effectively response to intracellular Hg2+ and PTO-doped Si-NPs were well uptaken by MCF-7 breast cancer cells. It could be concluded that the chromophores are promising materials used as biosensors.

In this study, two novel dual-switch fluorescent chemosensors based on rhodamine-peryleneiimide have been designed and synthesized. The dual-switching behaviors of the sensors were based on the structural transformations of rhodamine and an intramolecular photoinduced electron transfer (PET) process from rhodamine to perylenediimide. These probes exhibited excellent sensitivity to protons with enhanced fluorescence emission from 500 nm to 580 nm. The fluorescence changes of probes were reversible within a wide range of pH values from 2.0 to 11.0. Moreover, the sensors exhibited high selectivity, short response time, and long lifetime toward protons. The possible mechanism was investigated by the DFT calculation and 1H NMR. According to the experiment of confocal laser scanning microscopy, these probes could be used to detect the acidic pH variations in living cells.The dual-switching behaviors of the sensors were based on the structural transformations of rhodamine and an intramolecular photoinduced electron transfer process. The probes exhibited excellent sensitivity to protons with enhanced fluorescence emission from 500 nm to 580 nm.

•The naphthalimide-rhodamine dye exhibited the significant aggregation-induced emission enhancement.•AIE dye-doped silica nanoparticles were prepared and exhibited good solubility and stability in pure water.•FRET from the naphthalimide to the rhodamine was investigated by Hg2+-induced or H+-induced.A series of naphthalimide-rhodamine dye L1–4 with the different terminal structures were designed and synthesized. The rhodamine was used as bulky rigid substituent of naphthalimide to enhance the AIE property. All the naphthalimide-rhodamine dye exhibited the significant aggregation-induced emission enhancement. The strong fluorescence emissions in solid state were observed with emission peaks ranging from 549 to 608 nm. In high fW mixture solution, the fluorescence intensity enhanced with the increase of water content, which can be attributed to two types of aggregation-induced morphology. The AIE dye-doped silica nanoparticles (Si-NPs) were prepared and exhibited good solubility in pure water. In addition, dye L1 and L2 exhibited the selective recognition toward Hg2+ ions and were successfully applied to the bioimages in living cells. The intramolecular fluorescence resonance energy transfer mechanism from the naphthalimide moiety to the rhodamine moiety was investigated.A series of naphthalimide-rhodamine dye L1–4 with the different terminal structures were designed and synthesized. All the naphthalimide-rhodamine dye exhibited the significant aggregation-induced emission enhancement. In addition, the AIE dye-doped silica nanoparticles were prepared and the naphthalimide-rhodamine dye was successfully applied to the bioimages in living cells.

•We synthesize novel perylenediimide–naphthalimide fluorescent probes.•These FRET-based fluorescent probes exhibit efficient selectivity toward Fe(III) and protons.•Large perylenediimide–naphthalimide dendrons provide a new opportunity for near-infrared fluorescent probes.Two novel fluorescence resonance energy transfer-based perylenediimide–naphthalimide dendrons with perylenediimides as the energy acceptor, tertiary amines as the proton or metal receptor and naphthalimide as the energy donor were successfully synthesized. The dendrons exhibited high selectivity toward Fe(III) in the presence of various other metal cations and exhibited sensitivity to protons. A 1:2 stoichiometry was found for the complex formed by the probes and Fe(III) using a Job's plot and by non-linear least square fitting of the fluorescence titration curves. The probe molecules present abilities of fast fluorescence detection of Fe(III) and for the fluorescent detection of protons with high energy transfer efficiency of 96–98%.

Dye-loaded nanoparticles encapsulating four different aggregation-induced emission (AIE) and intramolecular charge transfer (ICT) active chromophores, which had different numbers of carbazole-containing triphenylamine moieties as donors and one 1,3,4-oxadiazole moiety as acceptor, were investigated and reported. Dye-doped amino-group-functionalized silica nanoparticles (Si-NPs), with diameter ∼30 nm, maintained the AIE characterized photophysical properties of the chromophores with high quantum yield up to 0.35 for oxa-(BCPA)1-doped Si-NPs, and the fluorescence emission peaks ranged from 476 nm to 513 nm for the four nanoparticles. Moreover, the dye-doped Si-NPs successfully overcome the challenges of the poor biocompatibility of AIE materials and could be efficiently dispersed in water, providing an important opportunity to further explore their bioapplications by conjugating the NPs with various biomolecules. The dye-loaded BSA-nanoparticles (BSA-NPs) were applied to cell imaging, which showed a better uptake by HeLa cells compared to pure dye NPs, which suggests its promising application for biosensors such as cancer cell detection.

A novel Schiff base-based multi-target dosimeter for Hg2+, Fe3+ and Au3+ has been designed and synthesized. Upon addition of Hg2+, Fe3+ and Au3+ to the aqueous solution of compound BODIPY-TRIA, the dosimeter gave a rapid fluorescence response and displayed an obvious fluorescence enhancement with a blue-shift. Meanwhile, a sharp color change from purple to pale yellow occurred, which was readily detected by the naked eye. The hydrolysis of the Schiff base promoted by Hg2+, Fe3+ and Au3+ has been discussed, and the possible mechanism was confirmed by 1H NMR and MS studies. The dosimeter showed high sensitivity (10 nM for Au3+), good stability, and excellent selectivity for Hg2+, Fe3+ and Au3+ with interference by other metal ions.

In this paper, a novel dendritic chemosensor was designed and synthesized. Specific dual-channel fluorescence sensing for Hg2+ was investigated. The probe represented dual recognition sites and segmented detection behaviors, which can be deduced to the dethioacetalization reaction promoted by Hg2+ and the coordination reaction between Hg2+ ions and the nitrogen atoms in the triazole rings of the probe. The probe was proved to selectively recognize Hg2+ ions in aqueous solution and it showed a high selectivity, a low detection limit (12 nM), a short response time, and a significant fluorescence enhancement (at 610 nm) with a high fluorescence resonance energy transfer efficiency (99%) between the energy donor and the energy acceptor. Moreover, the energy levels of the energy donor–acceptor pairs calculated by DFT were used to illustrate the different FRET efficiencies of the probe and the probe with Hg2+.

•We synthesize pyridine-end-capped triphenylamine chromophores (Py2-TPA)n.•These chromophores exhibit efficient three-photon excited green fluorescence.•Increasing the conjugation push-pull units will increase 3PA cross-sections.•Increasing extent of symmetrical charge transfer will increase 3PA cross-sections.•Large aromatic chromophores (Py2-TPA)n provide a new opportunity for 3PA-materials.Pyridine-end-capped triphenylamine derivatives (Py2-TPA)n (n = 1,2,4) were synthesized using palladium-catalyzed Heck reaction and characterized by 1H NMR, 13C NMR, and HRMS-MALDI-TOF. Three-photon absorption and three-photon excited fluorescence properties of chromophores (Py2-TPA)n were studied using a femtosecond Ti:Sapphire laser system. These chromophores exhibit efficient three-photon excited green fluorescence peaking at 540–590 nm. The three-photon absorption cross-section of σ3 = 6.99 × 10−79 cm6 s2 photon−2 in the femtosecond regime has been obtained from (Py2-TPA)4. The ratio of 3PA cross-sections in CH2Cl2 solution σ3 (Py2-TPA)4:σ3 (Py2-TPA)2:σ3 (Py2-TPA)1 is 6.0:4.2:1. The ratio of conjugated π-electron numbers in (Py2-TPA)n is 4.4(n = 4):2.6(n = 2):1(n = 1). The increasing the push–pull units of (Py2-TPA)n and π-electron conjugation length or increasing the extent of charge transfer from the ends to the middle aryl core results in an increase of the 3PA cross-section. The results indicate that large aromatic conjugated chromophores (Py2-TPA)n containing pyridine–triphenylamine D–A pairs and a conjugated aryl core provide a new opportunity for 3PA-materials and three-photon fluorophores for practical application.

The dendrimer PNS-G0 with Schiff-base imines (CN) realizes highly selective and common fluorescence (λex = 400 nm) or up-converted fluorescence (λex = 800 nm) turn-on effect to qualitatively and quantitatively detect zinc ions (Zn2+). The PNS-G0 + Zn2+ complex (CN_Zn_O) fluorescence emitting parts were firstly proposed as half-organic quantum dots (HOQDs). The HOQDs probe PNS-G0 for Zn2+ by the coordination method based on imine isomerization (inhibition) mechanism, which has potential applications in biological imaging, analytical chemistry, and optical physics areas.

The fluorescence emission phenomena of polyamidoamine (PAMAM) have been discovered and characterized in recent decades. The amide, primary amine, and tertiary amine groups are present in PAMAM, which are not the traditional or typical fluorescence emission groups. The fluorescence emission groups or mechanism of PAMAM were yet not clear but cause cares. In this study, PAMAM was characterized using NMR (15N NMR, 13C NMR, 1H NMR, and N–H 2D NMR), IR, and MS. The results proved that amide resonance structures, corresponding to imidic acid and tertiary ammonium groups, existed in PAMAM. The new imidic acid and tertiary ammonium groups found in PAMAM might help explain the intrinsic-fluorescence phenomena.

Organic dye two-photon absorption-induced frequency up-converted fluorescence (UCF) excited using a laser has been used in biological imaging and optical physics. The laser requires higher-level equipment that limits the application of UCF dyes. The experimental observation that the poly-amidoamine (PAMAM) pyridine derivatives 2PPS-G0 and 4PPS-G0 and those mixed with quantum dots (QDs) nanoparticles realized UCF using a common spectrofluorometer. The low-energy linear one-photon light source can also excite some organic molecules or QDs to give UCF emission, which replaces the need of a laser. The UCF related mechanism: second harmonic generation; two-photon absorption induced, and linear excited-states shifts (LESS) mechanisms were discussed to explain the linear one-photon light source excited UCF.

In recent decades, it has been found and determined that poly-amidoamine (PAMAM) can give fluorescence emission under certain conditions. PAMAMs possess amide, primary amine and tertiary amine groups, which are not typical fluorescence emission groups. The fluorescence emission centers and mechanisms of PAMAM were studied. In this report we used quantum chemical TDDFT methods to calculate the absorption and emission states of the chemical components of PAMAM, which including amide, amide resonance structure imidic acid, amine and ammonium groups. The theory calculations showed that the imidic acid and tertiary ammonium components can give emission. The mechanisms for the formation of the amide resonance structure imidic acid and tertiary ammonium were discussed. The calculation results show that the imidic acid and tertiary ammonium groups are responsible for the fluorescence emission of PAMAM, which might help to explain the intrinsic-fluorescence phenomenon.

Two symmetrical donor–acceptor–donor chromophores built by connecting two triphenylamine donors to a central electron acceptor 2,5-diphenyl-1,3,4-oxadiazole or anthracene core have been synthesized and characterized. The aggregation-induced emission phenomenon of these compounds with bright and deep emission from orange to green in the solid state can be obsreved. The chromophores based on the triphenylamine unit exhibit efficient solid-state emission. The results indicate that D–A–D conjugation bridging provides a new opportunity for AIE-materials. The multiphoton induced fluorescence spectra of these chromophores were measured using a femtosecond Ti:sapphire. The three-photon excited fluorescence spectra are in the green region with peaks at 554 nm for An-BIPAS and 504 nm for Ox-BIASP in THF, respectively. These AIE-active compounds are potential materials to design sensitive and selective fluorescent sensors or bioprobes.

Thirty-two molecules were designed as donor–bridge–acceptor (D–π–A) push-pull type nonlinear optical (NLO) chromophores with five-membered heterocyclic (O, S, NH, PH) bridges. An eigenvector following (EF) method was employed to optimize the structures of the molecules and a parametric method number six (PM6) method was used to study the second-order NLO properties by calculating the dipole moment and the first- and second-order polarizabilities. The relationship between second-order NLO properties and the structures is discussed through the calculated results. The analyzed results show that the five-membered heterocyclic ring is a highly efficient electronic transfer bridge. By comparing the second-order NLO properties, it was found that the 4H-1,2,4-diazaphosphole heterocyclic bridge (MZ-PH) and furan heterocyclic bridge (M-O) can enhance the second-order polarizability (β) values of molecules more than other bridges. The results can help the selection of electronic donor, conjugated bridge and electronic acceptor to get large second-order NLO properties.

Triphenylamine core multipolar derivatives were synthesized via the Wittig reaction and Heck reaction and were characterized by MS, NMR, IR; melting points and decomposition temperatures were determined using differential scanning calorimetry. The photophysical as well as the linear and nonlinear spectral properties of multipolar compounds with a triphenylamine core were compared to those of corresponding dipolar compounds. The multipolar chromophores displayed large two-photon absorption and strong optical power limiting properties. An extended π-conjugated system and increased intramolecular cooperative effect are responsible for the observed, large two-photon absorption character.

Novel azo diol chromophores were synthesized through multi-step azo-coupling reaction and characterized by NMR, IR, and UV. The third-order NLO properties of the chromophores were investigated. The measurements of second hyperpolarizabilities were performed using single-beam Z-scan technique with picosecond laser pulses at 1064 nm in DMF solutions. Our results indicate that larger second hyperpolarizabilities γ can be readily obtained in such chromophores because of increase of molecular conjugation length and donor–acceptor conjugation path. Further enhancement of γ has been achieved via replacement of phenyl rings in the conjugated backbone by heteroaromatic spacers such as benzothiazole and pyrimidine rings. Therefore, it is very probable that the increase in the obtained γ values considerably arises from the conjugation path of the delocalized electrons for large third-order nonlinear optical effects.

Nonlinear optical chromophores with nitro acceptors have been designed and synthesized. The first-order hyperpolarizability of the chromophores was determined using hyper-Rayleigh scattering; the decomposition temperature was determined using DSC and the absorption spectra of the compounds were measured. The nonlinear optical properties of the chromophores were discussed; the first-order hyperpolarizabilities of chromophores 3 and 4 come from their two-dimensional structure, the length of the conjugation bridge and intramolecular proton transfer. The strong dihydroxyl donor of chromophores 1 and 2 expanded the first-order hyperpolarizabilities, the measured βHRS values of chromophores 1 and 2 at 1064 nm are 211 × 10−30 esu and 177 × 10−30 esu, respectively. These NLO-chromophores exhibit higher decomposition temperature in the range of 290–330 °C.

Two symmetrical 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles that exhibit strong two-photon absorption and enhanced two-photon excited fluorescence were designed and synthesized based on “push-core-pull-core-push” molecules built from embedding electron-transporting 1,3,4-oxadiazole in aromatic conjugated system through Wittig–Horner reaction. Pumped by nanosecond laser at 800 nm, strong up-conversion emissions with the central wavelength at 507 nm (green) of 2,5-bis[4-(2-N,N-diphenylaminostyryl)phenyl]-1,3,4-oxadiazole and 475 nm (blue) of 2,5-bis[4-{2-(3-N-ethylcarbazolyl)vinyl}phenyl]-1,3,4-oxadiazole in the solution of CHCl3 have been observed. Their two-photon absorption cross-sections obtained by nonlinear transmission method are 107 × 10−48 cm4 s photon−1 and 66 × 10−48 cm4 s photon−1. A very effective energy transfer from the excited terminal units to the π-conjugated bridging units of the 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles is the dominant contribution to the two-photon absorption.

Four novel 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles that exhibit strong two-photon absorption and enhanced two-photon excited fluorescence were designed and synthesized based on “push-core-pull-core-push” molecules built from embedding electron-transporting 1,3,4-oxadiazole in aromatic conjugated system through Wittig-Horner reaction. Their chemical structures were determined to show trans-vinylene character according to infrared (IR) and 1H nuclear magnetic resonance (NMR) spectra. A very effective energy transfer from the excited units to the π-conjugated bridging unit can enhance the two-photon absorption and two-photon fluorescence.

Novel A-π-D-π-A carbazole-cored chromophores were synthesized and characterized by NMR, IR, UV techniques. The third-order NLO properties of the carbazole chromophores were investigated. The measurements of second-order hyperpolarizabilities were performed using single-beam Z-scan technique with picosecond laser pulses in DMF solutions. Our results indicate that larger second-order hyperpolarizabilities γ can be readily obtained in such carbazole chromophores because of increasing strength of withdrawing group and molecular conjugation length with two aromatic bridges in the two-dimensional conjugated system. Therefore, it is very probable that the increase in the obtained γ values considerably arises from the conjugation path of the delocalized electrons for large third-order nonlinear optical effects.

Nonlinear optical multipolar chromophores with nitro acceptors were designed and synthesized. The target compounds were characterized by NMR, IR, UV and melting point. The decomposition temperature was determined with differential scanning calorimetry, and the absorption spectra were measured. The first hyperpolarizability of the chromophore were calculated via solvatochromic methods. The nonlinear optical properties of five compounds were discussed. Especially, the first-order hyperpolarizabilities of chromophores 2 and 3 come from their two-dimensional structure, the length of the conjugation bridge and the intramolecular proton transfer. The strong dihydroxyl donor of chromophores 4 and 5 expanded the first-order hyperpolarizabilities. These NLO chromophores exhibit large optical nonlinearity, good transparency and thermal stability.

Thirty-two molecules were designed as donor–bridge–acceptor (D–π–A) push-pull type nonlinear optical (NLO) chromophores with five-membered heterocyclic (O, S, NH, PH) bridges. An eigenvector following (EF) method was employed to optimize the structures of the molecules and a parametric method number six (PM6) method was used to study the second-order NLO properties by calculating the dipole moment and the first- and second-order polarizabilities. The relationship between second-order NLO properties and the structures is discussed through the calculated results. The analyzed results show that the five-membered heterocyclic ring is a highly efficient electronic transfer bridge. By comparing the second-order NLO properties, it was found that the 4H-1,2,4-diazaphosphole heterocyclic bridge (MZ-PH) and furan heterocyclic bridge (M-O) can enhance the second-order polarizability (β) values of molecules more than other bridges. The results can help the selection of electronic donor, conjugated bridge and electronic acceptor to get large second-order NLO properties.

Hypochlorite serves as a significant antimicrobial agent in the human immune system, and its detection is of great importance. Herein, a novel near-infrared BODIPY-based ClO− fluorescent probe (NCS-BOD-OCH3) was designed and synthesized. The emission bands of NCS-BOD-OCH3 concentrated at 595 nm and 665 nm. Since the electron withdrawing group 1,3,4-oxadiazole was formed after the desulfurization reaction, the fluorescence intensity of NCS-BOD-OCH3 decreased significantly in THF/H2O (v/v, 1:1, buffered with 10 mM PBS pH = 7.4), which is visible to the naked eye with an obvious color change. NCS-BOD-OCH3 can realize the two-photon up-converted fluorescence emission. The low detection limit was calculated from the titration results, with the figure for NCS-BOD-OCH3/ClO− being 1.15 × 10−6 M. The result of living cell imaging experiment demonstrated that NCS-BOD-OCH3 can successfully detect ClO− in living cells and can serve as a NIR mitochondrial imaging agent. It is an excellent platform for developing NIR ClO− fluorescent probes.

A novel triphenylamine-BODIPY based Schiff base fluorescent probe (TPA-BODIPY-OH) with an emission in the near-infrared (NIR) region was designed and prepared by click reaction. TPA-BODIPY-OH showed three emission bands at 510 nm, 598 nm and 670 nm, and can detect Fe3+ and Hg2+ ions with remarkable fluorescence enhancement in THF/H2O (v/v, 1:1, buffered with 10 mM HEPES pH = 7.4) based on the hydrolysis reaction of the –CN bond, and naked eye detection was realized with an obvious color change. The stoichiometry between the probe and ions was deduced from a Job's plot, which is 1:3 for TPA-BODIPY-OH/Fe3+ and 1:2 for TPA-BODIPY-OH/Hg2+, respectively. The dissociation constant value was found to be 1.35 × 10−16 M for TPA-BODIPY-OH/Fe3+ and 2.06 × 10−11 M for TPA-BODIPY-OH/Hg2+. The low detection limit was calculated from the titration results with the values of 5.15 × 10−7 M for TPA-BODIPY-OH/Fe3+ and 6.81 × 10−7 M for TPA-BODIPY-OH/Hg2+, respectively. In order to investigate the biological applications of TPA-BODIPY-OH, a living cell imaging experiment was carried out. The results demonstrate that TPA-BODIPY-OH can be successfully applied as a bioimaging agent in living cells. In addition, amino-group-functionalized silica fluorescent nanoparticles (FNPs) encapsulating the TPA-BODIPY-OH dyes were prepared and characterized by transmission electron microscopy. TPA-BODIPY-OH/SiO2 nanoparticles exhibit good dispersibility, and the quantum yield of FNPs at 657 nm was 42.3%.