Multi-stimuli programmable FRET based RGB absorbing antennae towards ratiometric temperature,pH and multiple metal ion sensing

A red-green-blue (RGB) multichromophoric antenna 1 consisting of energy donors naphthalimides and perylenediimides and a central aza-BODIPY energy acceptor along with two subchromophoric red-blue (RB 6) and green-blue (GB 12) antennae was designed that showed efficient cascade Förster resonance energy transfer (FRET). RGB antenna 1 showed pronounced temperature-dependent emission behaviour where emission intensities in green and red channels could be tuned in opposite directions by temperature giving rise to unique ratiometric sensing with a temperature sensitivity of 0.4% °C. RGB antenna 1 showed reversible absorption modulation selectively in the blue region (RGB ↔ RG) upon acid/base addition giving rise to pH sensing behaviour. Furthermore, RGB antenna 1 was utilized to selectively sense metal ions such as Co²⁺ and Fe³⁺ through a FRET turn-off mechanism induced by a redox process at the aza-BODIPY site that resulted in the selective spectral modulation of the red band (i.e., RGB → GB). Model antenna RB 6 showed white light emission with chromaticity coordinates (0.32, 0.33) on acid addition. Antennae 1, 6 and 12 also exhibited solution state electrochromic switching characterized by distinct colour changes upon changing the potential. Finally, antennae 1, 6 and 12 served as reversible fluorescent inks in PMMA/antenna blends whereby the emission colours could be switched or tuned using different stimuli such as acid vapour, temperature and metal ions.

RGB antennae consisting of naphthalimides, perylenediimides and aza-BODIPY with efficient FRET show unique ratiometric temperature sensing, metal sensing (FRET-off) and pH sensing through various stimuli sensitive band tuning.     

Broken time-reversal symmetry in strongly correlated ladder structures

We provide, for the first time, in a doped strongly correlated system (two-leg ladder), a controlled theoretical demonstration of the existence of a state in which long-range ordered orbital currents are arranged in a staggered pattern, coexisting with a charge density wave. The method used is the highly accurate density-matrix renormalization group technique. This brings us closer to recent proposals that this order is realized in the enigmatic pseudogap phase of the cuprate high temperature superconductors.     

Ion detection with photonic crystal microcavities

We have experimentally demonstrated a cation and anion sensor by using short linear photonic crystal microcavities with an embedded quantum dot active region. The photonic crystal microcavity covered with an ion-selective polymer forms a submicrometer optical detection system sensitive to small changes of perchlorate anion (ClO4(-)) and calcium cation (Ca2+) concentrations.     

The disappearance of equatorial E s and the reversal of electrojet current

Based on simultaneous observations of the horizontal geomagnetic field component H, sporadic E (E _s ) and E-W electron drifts at stations close to the dip equator within the equatorial electrojet region, it has been found that on quiet days and sometimes on disturbed days, when there is an abnormal large decrease in H during daytime, there is a simultaneous disappearance of E _s and a reversal of the direction of drift of electrons from westward to eastward. This suggests that the disappearance of equatorial E _s during day-time is due to a temporary reversal of the electrojet current, which is caused by the imposition of an additional electrostatic field opposite in direction to that of normal S _a field.     

Sharp signature of a dx2-y2 quantum critical point in the Hall coefficient of cuprate superconductors

We study the behavior of the Hall coefficient, R(H), in a system exhibiting dx(2)(-y(2)) density-wave order in a regime in which the carrier concentration, x, is tuned to approach a quantum critical point at which the order is destroyed. At the mean-field level, we find that n(Hall)=1/R(H) evinces a sharp signature of the transition. There is a kink in n(Hall) at the critical value of the carrier concentration, x(c); as the critical point is approached from the ordered side, the slope of n(Hall) diverges. Hall transport experiments in the cuprates, at high magnetic fields sufficient to destroy superconductivity, should reveal this effect.     

Catalytic and kinetic study of the liquid-phase hydrogenation of various organic substrates over a polymer-anchored Pd(II) catalyst

A polymer-anchored Pd(II) complex has been prepared and characterized using scanning electron microscopy, elemental analysis, atomic absorption spectroscopy and FTIR. The catalyst shows excellent catalytic activity in the liquid-phase hydrogenation of substituted nitrobenzenes at normal pressure of hydrogen gas at 25 °C in DMF medium. We have also studied the liquid-phase hydrogenation of other organic substrates such as alkenes, alkynes, aromatic aldehydes, etc. The influences of various parameters such as amount of catalyst, concentration of substrate, temperature and solvent have been studied. The catalyst can be used five times without much loss in activity.     

A reusable polymer supported copper catalyst for the C–N and C–O bond cross-coupling reaction of aryl halides as well as arylboronic acids

A simple and industrially viable protocol for C–N and C–O coupling was reported here. The polymer supported heterogeneous copper catalyst was prepared from chloromethyl polystyrene using a simple procedure. O-Arylation of substituted phenols with various aryl halides was achieved using this copper catalyst in DMSO medium. This heterogeneous copper catalyst, also efficiently works for the N-arylation of N–H heterocycles with aryboronic acids in methanol. This catalyst was also effective in amination reaction of primary amines with aryl halides as well as arylboronic acids in DMSO medium. The effects of solvent, base and temperature for the O-Arylation and amination reactions were reported. Further, the catalyst can be easily recovered quantitatively by simple filtration and reused up to several times without sufficient loss of its catalytic activity.     

Theoretical Study on the Formation of H‐ and O‐Atoms,HONO, OH,NO, and NO2 from the Lowest Lying Singlet and Triplet States in Ortho‐Nitrophenol Photolysis

The photolysis of nitrophenols was proposed as a source of reactive radicals and NOx compounds in polluted air. The S₀ singlet ground state and T₁ first excited triplet state of nitrophenol were investigated to assess the energy dependence of the photofragmentation product distribution as a function of the reaction conditions, based on quantum chemical calculations at the G3SX//M06–2X/aug‐cc‐pVTZ level of theory combined with RRKM master equation calculations. On both potential energy surfaces, we find rapid isomerization with the aci‐nitrophenol isomer, as well as pathways forming NO, NO₂, OH, HONO, and H‐, and O‐atoms, extending earlier studies on the T₁ state and in agreement with available work on other nitroaromatics. We find that accessing the lowest photofragmentation channel from the S₀ ground state requires only 268 kJ/mol of activation energy, but at a pressure of 1 atm collisional energy loss dominates such that significant fragmentation only occurs at internal energies exceeding 550 kJ/mol, making this surface unimportant for atmospheric photolysis. Intersystem crossing to the T₁ triplet state leads more readily to fragmentation, with dissociation occurring at energies of ～450 kJ/mol above the singlet ground state even at 1 atm. The main product is found to be OH + nitrosophenoxy, followed by formation of hydroxyphenoxy + NO and phenyloxyl + HONO. The predictions are compared against available experimental data.