Synthesis of Novel Blue and Green Light Emitting 4-Nitrophenol Luminophors for Optoelectronics Abstract The number of anthracene (AN) and anthracene-tetracene (AN-TN) doped 4-nitrophenol (4-NP) luminophors (AN/4-NP and AN-TN/4-NP) were prepared at different proportion by conventional technique called solid state reaction. Excitation energy transfer was observed by fluorescence spectroscopy and cyclic voltammetry. 4-NP acts as an outstanding light emitting matrix. The effect of the donor emission was perceived by changing the dopant concentration; this showed that AN/4-NP and TN-AN/4-NP exhibit fluorescence emission ranging from blue to green i.e. in the range from 400 to 525 nm and 535–550 nm, respectively. Structural properties and thermal stability was studied by XRD, SEM and TGA-DSC techniques. The study reveals that the prepared materials show excellent properties which can meet the demands of optoelectronic devices as well as for light emitting devices.

Synthesis of Strongly Fluorescent Imidazole Derivatives: Structure Property Studies, Halochromism and Fluorescent Photoswitching Abstract New series of methoxy and hydroxyl group substituted triphenylamine (TPA)-imidazole fluorescent molecules (5-(diphenylamino)-2-(1H-phenanthro[9,10-d]imidazol-2-yl)phenol (1), 5-(diphenylamino)-2-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)phenol (2), 5-(diphenylamino)-2-(4,5-diphenyl-1H-imidazol-2-yl)phenol (3), 5-(diphenylamino)-2-(1,4,5-triphenyl-1H-imidazol-2-yl)phenol (4), N-(3-methoxy-4-(1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)-N-phenylbenzenamine (5), N-(3-methoxy-4-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)-N-phenylbenzene amine (6), and N-(3-methoxy-4-(4,5-diphenyl-1H-imidazol-2-yl)phenyl)-N-phenylbenzenamine (7)) have been synthesized that exhibited strong solution fluorescence and molecular structure and conformation controlled fluorescence photoswitching, solid state fluorescence and halochromism. Hydroxyl substituted molecules (1–4) showed moderate to strong fluorescence in solution depend on solvent polarity and very weak solid state fluorescence. Methoxy substituted molecules (5–7) displayed strong fluorescence both in solution and solid state. Solid state structural studies revealed strong intramolecular H-bonding in the crystal lattice. Interestingly, highly twisted structure (6) showed rare light induced reversible fluorescence switching in CHCl3. The observation of isobestic point in time dependent fluorescence photoswitching studies indicated structural isomer conversion. Further, acid sensitive imidazole nitrogen has been made use to demonstrate solid state fluorescence switching via halochromism. Thus the present studies attempted to develop new fluorescent molecules and establish structure-property relationship for designing fluorescence switching materials. Graphical Abstract Molecular structure controlled solid state fluorescence, halochromism and a rare fluorescence photoswitching in chloroform have been observed with triphenylamine-imidazole derivatives.

Spectroscopic Study of Aggregation of Carbazole Units Abstract Several fluorescence spectral features in aggregation of carbazole unites have been reported in previous study. Unfortunately, the influence of inner filter effect has not been paid enough attention. In this work, aggregation of carbazole unites resulting from increasing concentration or decreasing solvent affinity, was investigated by fluorescence spectroscopy. Through comparison between the spectra of two aggregation processes, it is found that only intensity ratio of 0–0 transition to 0–1 transition in excitation/emission spectra is sensitive to aggregation states. There is an obvious decrease in that intensity ratio upon aggregation. On the other hand, other spectral features observed in previous research such as intensity decrease in S0 → S2 transition and emission quenching in concentration induced aggregation process, should be induced by inner filter effect. Graphical Abstract

An Application of a Schiff-Base Type Reaction in the Synthesis of a New Rhodamine-Based Hg(II)-Sensing Agent Abstract A facile synthesis procedure, whereby 9-Anthraldehyde (AA) is coupled to aminated rhodamine (AR) via a Schiff base-type reaction, is reported. The applicability and performance of the obtained material (AA-AR) as a sensing agent was studied towards 16 metal cations (i.e. Li+, Na+, Ag+, Ca2+, Ba2+, Co2+, Cs+, Cu2+, Mg2+, Hg2+, Mn2+, Pb2+, Ni2+, Sr2+, Zn2+, Al3+). Among the studied metals, an extraordinary selectivity was observed for Hg2+, and the observed selectivity was found not to be influenced by the presence of other cations and some common anions (i.e. Br−, Cl−, I−, HPO42−, H2PO4−, NO3−, NO2−, ClO4−, AcO−, HSO4−, SO42−, Cr2O7−, CO32−, OH− and HCO3−). The material, AA-AR, exhibited such a high selectivity and sensitivity towards Hg2+ that it could be detected even by naked eyes. The Hg2+-sensing property of AA-AR was found not to be limited to colorimetric detections so that a high fluorescent nature of the compound was also observed upon binding Hg2+ ion. The detection limit, which is correspondent to fluorescence emission intensity, was found as 0.87 μM. The underlying mechanism of sensing property was studied by using some spectroscopic techniques such as FT-IR, 1H-NMR, 13C-NMR, and UV-Vis. (Job-plot). In the final course of the experiments, the performance of AA-AR in cell-imaging was also studied, and even trace amounts of Hg2+ in living cells could be detected by the studied probe. Thus, the applicability of a new synthesis approach in producing a highly efficient new fluorescence sensor for the detection of Hg2+ ions is discussed in detail.

Spectroscopic Properties of some Hydroxylated 2-Stilbazole Derivatives Abstract The spectroscopic properties for a number of new hydroxylated 2-stilbazoles were studied by absorption and fluorescence spectroscopy. The maximum absorption and emission wavelengths, the molar extinction coefficients, and the Stokes shift values of derivatives were given. The dependence of the spectral characteristics on pH was shown. The possibility of creating molecular logic systems and fluorescent dyes for bioimaging based on these derivatives was demonstrated. The dependence of fluorescence on the medium redox properties was established for an one of derivatives. The possibility of a fluorescent probe creating on its basis to assess the oxidative state of living systems was demonstrated. The probe has good biocompatibility and can be successfully used for fluorescence imaging in cells.

Photoinduced Reversible Modulation of Fluorescence of CdSe/ZnS Quantum Dots in Solutions with Diarylethenes Abstract Steady-state absorption and fluorescence spectra, fluorescence decay kinetics of CdSe/ZnS quantum dots (QD) with photochromic diarylethenes (DAE) in toluene have been studied. Two kinds of QDs emitting at 525 and 600 nm were investigated and DAE were selected to ensure good overlap of their photoinduced absorption band with QDs emission spectra. It has been found that photochromic molecules form complexes with QD which results in partial fluorescence quenching. A reversible modulation of QDs emission intensity which correlates with magnitude of transient photoinduced absorption band of the diarylethenes during photochromic transformations has been demonstrated.

A Novel Fluorescent Chemosensor for cu (II) Ion: Click Synthesis of Dual-Bodipy Including the Triazole Groups and Bioimaging of Yeast Cells Abstract A fluorescent chemosensor including dual Bodipy units (d-BODIPY) was improved for selective copper (II) sensing in half-aqueous samples. The sensor d-BODIPY has a highly selective and sensitive detection towards Cu (II) over the studied competing for metal cations. The interaction among solutions of Cu (II) and d-BODIPY caused a crucial quenching effect in fluorescence maxima at 548 nm (λex = 470 nm) owing to the electronic trap occurring between the amide and triazole units. The quenching effect without any change in wavelength can be explained by a photoinduced electron transfer (PET) process. The binding constant (Ka) of d-BODIPY with Cu (II) was calculated and also the limit of detection of d-BODIPY for Cu (II) was 1.2 × 10−8 M. In addition, the bio-imaging in the yeast cells suggested that d-BODIPY had an excellent potential to be used to investigate Cu (II).

Optical Properties of Methyl Orange-Doped Droplet and Photodynamic Therapy of Staphylococcus aureus Abstract Dye-doped droplets are known as mixtures of dyes with uniform solutions of water droplets in a continuous phase of oils with surfactants. To observe the relationship between water droplet structures and surfactant types on optical properties of dyes, a mixture of methyl orange (MO)-doped droplet prepared with benzane and hexane as oils and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) as a surfactant was thus examined using Z-scan instrument, spectrophotometer, and fluorimeter in the present study. The findings revealed that nonlinear refractive (NLR) index, nonlinear absorption (NLA) coefficient, as well as fluorescence intensity of the MO had enhanced following a reduction in the droplet water content induced by changes in the non-centrosymmetric charge density distribution of this pH indicator. Moreover, the MO-doped droplet in a continuous phase of benzene investigated by 1H nuclear magnetic resonance (NMR) spectroscopy indicated that the MO had been located in the droplet in the vicinity of the hydrophilic part of the surfactant. Furthermore, the MO-doped droplets along with laser radiation were employed to perform antibacterial photodynamic therapy (APDT) of Staphylococcus aureus (S. aureus). It was ultimately concluded that the bacteria colony had also extremely diminished in the group treated by the MO-doped droplet.

Fluorescent N/Al Co-Doped Carbon Dots from Cellulose Biomass for Sensitive Detection of Manganese (VII) Abstract Development of metallic and nonmetallic heteroatom doped carbon dots have gained attention due to their enhanced physicochemical and photoluminescence properties. In this study, a facile one pot hydrothermal carbonisation approach was taken to synthesise nitrogen, aluminum co-doped carbon dots (N/Al-CDs) with a photoluminescence quantum yield of 28.7%. Durian shell, a cellulose biomass waste, was used as the primary carbon source and compared to previously reported cellulose based carbon dots, this study presents one of the highest quantum yields. The structural and fluorescent properties of the synthesised N/Al-CDs were characterized through X-ray photoelectron spectroscopy (XPS), fluorescence spectra, and Fourier transform infrared spectroscopy (FTIR). The maximum emission was at 415 nm upon excitation at 345 nm. The synthesised N/Al-CDs were resistant to photobleaching and highly photostable within the pH, ionic strength and temperature variations investigated. The transmission electron microscopy (TEM) images showed particles were quasi-spherical and well dispersed with an average diameter of 10.0 nm. Further, the N/Al-CDs was developed as a fluorescence sensor for highly selective and sensitive detection of Mn (VII) ions. A linear relationship was developed over a concentration range of 0–100 μM while the limit of detection was 46.8 nM. Application of the sensor for detection of Manganese (VII) to two real water samples showed relative standard deviation was less than 3.9% and 1.3%, respectively.

Realization of Optical Network Structures for Robust Films through Immobilization of Europium Complexes Abstract In this study, the bio-inspired self-cracking substrate can be employed as a template to control the formation of a robust mirco-patterning film. Uniform materials with variable diameters are achieved by optimizing the egg white/water ratios and reaction temperature. The incorporated europium ions exhibit its typical f-f transitions in patterned films. Moreover, the mechanical property and excellent transmittance features have been demonstrated. The current approach can be extended to design two-dimensional nanofabrication of different materials.