Polycyclic Organic Molecules Research Articles

Porous Silica as a Nanotemplate for the Solid State and Liquid Phase Synthesis of Luminescent Carbon Dots

Samples of nanoporous silicon oxide (pore size of 40 nm and 6 nm with specific are of 90 m2/g and 233 m2/g respectively) were synthesised by sol-gel method and used as nanotemplate for solid stated and liquid phase synthesis of lluminescent carbon nanodots (nanoagregates). Solid state method was two step process of chemical treatment of porous silicas by toluene solution of phenylstrimethoxisilane followed by pyrolysis at temperature in range of 400-600 0C for 60-180 minutes. Three characteristic emission bands in UV and VIS spectral range (360-380 nm, 410-420 nm, 440-450 nm) and their combinations were found in annealed por-SiO2:C depending on annealing time and temperature. The nature of light emission of pyrolytic carbon moieties in SiO2:C nanopowder was analysed and discussed in frame of the concepts of polycyclic carbon clusters and their aggregates based on the analogy with polycyclic organic molecules and luminescent carbon nanodots. It is suggested to assign the characteristic emission bands at about 380 nm and 420 nm to polycyclic carbon fluorophores with 2- and 3-ring structure respectively. The other low energy characteristic emission bands at wavelength 440-450 nm and higher are assigned to amorphous nanoaggregates. It is found that PL intensity of por-SiO2:C nanocomposite is sensitive to the absorption of the air. Response of the PL on absorption/desorption of air moieties was studied and discussed.Hydrophylic carbon nanodots were synthesized by liquid phase thermolysis of sucrose in dimethyl sulfoxide solution at 200 0C that resulted in formation of luminescent colloid. Porous silica were infiltrated by this colloid and then dried. Luminescent moieties absorbed in porous silicas were then extracted in water resulting in aqueous solution that exhibited intense visible photoluminescence with maximum intensity at 430-440 nm and well pronounced excitation band at 360-400 nm. This emission is suggested to be assigned to hydrophilic amorphous carbon nanodots (nanoagregates). Examination of Z-parameter of the colloids gave a value of the size of carbonnanodots below 1 nm. Spectral parameters (maximum position and spectral width) of the emission and excitation of photoluminescence were found to be dependent on the size of the pores in porous silica template that can be assigned to the effect of the size and size distribution of carbon nanodots (nanoagregates).As a summary, it was shown that nanoporous silica with high specific surface area can be used as solid state “container” for both solid state and liquid phase synthesis of carbon nanoemitters with emission spectrum variable from the near UV to the visible.

Evolution from UV emission of phenyl groups to visible emission of pyrolytic nanocarbons dispersed in fumed silica: Alternative insight into photoluminescence of carbon nanodots

SiO2:C nanopowder, luminescent in ultraviolet and visible spectral ranges, was synthesised using fumed silica as morphological matrix (specific surface of 295 m2/g) and phenyltrimethoxysilane (PhTMS) as carbon precursor. Fumed silica was impregnated by toluene solution of PhTMS followed by drying and annealing at 600 °C. Two series of SiO2:C nanocomposites with different carbon concentration were synthesised and studied. The main idea of the study was to explore the correlation of structural reconstruction and evolution of photoluminescent properties of carbon moieties. Chemically modified fumed silica exhibited ultraviolet (UV) photoluminescence band at about 330 nm originated from phenyl groups. After calcinations at 600 °C two overlapped emission bands were found at about 380 nm and 420 nm in “low-carbon” SiO2:C, while “high-carbon” series exhibited broad but homogeneous emission band peaked at about 440–450 nm. One more characteristic emission band at 495 nm in SiO2:C appeared and developed under intense ultraviolet radiation. Evolution of light emission from ultraviolet to visible was analysed in correlation with structural reconstruction of carbon examined by FTIR spectroscopy, X-ray photoelectron spectroscopy, high resolution scanning transmission electron microscopy, and electron energy loss spectroscopy. The nature of light emission of pyrolytic carbon moieties in SiO2:C nanopowder was discussed in frame of the concepts of polycyclic carbon clusters and their aggregates based on the analogy with polycyclic organic molecules and luminescent carbon nanodots.

Isolated π-Interaction Sites in Mesoporous MOF Backbone for Repetitive and Reversible Dynamics in Water.

We report the introduction of π-interaction sites into a series of chemically robust metal-organic frameworks (MOFs), MOF-526, -527, and -528, with progressively increased pore size, 1.9-3.7 nm, and the inclusion and release of large organic molecules in water. The mesopores in these MOFs lead to fast adsorption kinetics, whereas the π-interaction between isolated porphyrin units in the MOF backbone and polycyclic structure of the organic guests provides excellent reversibility. Specifically, seven large organic dyes were quantitatively captured by the porphyrin units of these MOFs in a 2:1 molar ratio, exhibiting unprecedented kinetics for MOFs [e.g., 4.54 × 105 L/mol for rhodamine B] at an extremely low concentration (10 ppm) in water. Rotational-echo double-resonance NMR experiments revealed that the distance between the guest molecules and porphyrin units in MOFs was in the range from 3.24 to 3.37 Å, confirming the specific π-interaction. Repetitive and reversible dynamics was achieved in these MOFs for 10 complete inclusion-release cycles without any decay in performance, which is ideally suited for the removal and recycle of large polycyclic organic molecules from water. The performance of MOF-526 rivals that of state-of-the-art carbon and polymers.

Enabling DPP derivatives to show multistate emission and developing the multifunctional materials by rational branching effect

Conventional polycyclic organic molecules exhibit aggregation-caused quenching (ACQ) effect, and some organic molecules with twisted and propeller backbones could be made into aggregation-induced/enhanced emission (AIE/AEE). However, it was interesting but challenging to enable conjugated molecules derived from fused (hetero)cycles with high photo- and thermal-stability to show multistate emission, rather than only dual emission in solution and crystalline states. In the current work, we presented a rational strategy for realizing multistate emission of 1,4-diketo-pyrrolo [3,4-c]pyrrole (DPP) derivatives by employing imidazole as the additional acceptor bridge and constructing the branched DPP-centered molecule with four peripheral donors (triphenylamine). The resulting D‒A‒D compound (TIDPP) emitted yellow in solution with the fluorescence efficiency of ca. 70%, and its crystalline and amorphous states as well as aqueous suspensions also exhibited impressive fluorescence efficiencies of 40–50%, filling the gap between ACQ and AIE of DPP derivatives. Moreover, aggregation could greatly red-shift emission spectra and significantly enhance the two-photon absorption cross section and excitation fluorescence in the aqueous suspension. TIDPP solid was also found to exhibit the unique mechanochromic blue-shift luminescence and the commendable OFET performance, signifying the existence of aggregation-induced molecular planarization. This work demonstrated that the rational branching effect could manipulate the aggregation emission behaviors and develop the multifunctional materials.

Graphite Oxide and Aromatic Amines: Size Matters

Experimental and theoretical studies are performed in order to illuminate, for first time, the intercalation mechanism of polycyclic aromatic molecules into graphite oxide. Two representative molecules of this family, aniline and naphthalene amine are investigated. After intercalation, aniline molecules prefer to covalently connect to the graphene oxide matrix via chemical grafting, while napthalene amine molecules bind with the graphene oxide surface through π–π interactions. The presence of intercalated aromatic molecules between the graphene oxide layers is demonstrated by X‐ray diffraction, while the type of interaction between graphene oxide and polycyclic organic molecules is elucidated by X‐ray photoelectron spectroscopy. Combined quantum mechanical and molecular mechanical calculations describe the intercalation mechanism and the aniline grafting, rationalizing the experimental data. The present work opens new perspectives for the interaction of various aromatic molecules with graphite oxide and the so‐called “intercalation chemistry”.

Thermo-dynamical contours of electronic-vibrational spectra simulated using the statistical quantum–mechanical methods

Three polycyclic organic molecules in various solvents focused on thermo-dynamical aspects were theoretically investigated using the recently developed statistical quantum mechanical/classical molecular dynamics method for simulating electronic-vibrational spectra. The absorption bands of estradiol, benzene, and cyanoanthracene have been simulated, and most notably, the increase in the spectral intensity for the lowest excited state transition as the temperature is increased observed experimentally is well reproduced. In addition, this method has been extended to treat luminescent processes also, and it is seen that the experimental emission spectrum of cyanoanthracene is also well described. The method still needs further refinement, but results to date, including those presented in this work, document clearly that our model is one which is able to treat the many complex effects that the environment have on electronic absorption and emission spectra.

Determinations of Intermediate Neutral Species in Hydrocarbon Discharge Plasma

This work reports laser ionization combined with Time-Of-Flight (TOF) mass spectrometry investigation on intermediate species in the hydrocarbon plasma of atmospheric-pressure fast-flow pulsed dc-discharge. All neutral intermediate species including transient radicals from benzene/Ar discharge have been characterized by a molecular beam sampling combined with TOF mass spectrometry. This shows that with a hydrocarbon gas mixture of 0.3% C6H6 in Ar discharge the intermediate species consist of simple radicals (such as C2, C5H5, C7H7) and polycyclic organic molecules (C10H8, C13H10, C14H10). Theoretical studies on total energies and ionization potentials of the intermediate species have been carried out using the hybrid density functional theory. Effect of the ionization potential on mass spectral intensity has been discussed. Based on the observed data, the possible major neutral reaction channels of the plasma chemistry have been discussed. The developed experimental method has implications in volatile organic compounds removing and impurities diagnosis in Tokamak edge-plasma.

Quantum chemical study of the electron affinity of the diimino derivatives of mono- and polycyclic organic molecules

Electron affinities (EA) of several aromatic compounds and their diimino-derivatives were calculated quantum chemically at B3LYP/6-31+G(d) level. Addition of imino groups increases the EA of the molecules up to 2–2.5 eV. Among the most promising compounds, which can serve as ligands with versatile charge states are diiminoanthracene and diiminonaphthalene. It was shown that aryl fragments in bis[N-(2,6-diisopropylphenyl)imino]acenaphthene do not take part in accepting attached electrons.

Natural bond orbital dissection of fluorine–fluorine through-space NMR coupling (JF,F) in polycyclic organic molecules

A new approach to deconvolute DFT and ab initio Fermi contact-derived NMR coupling constants into conceptually familiar localized orbital contributions (NJC analysis) is exemplified by analysis of through-space J(F,F) couplings in a few illustrative cases.

An extended scheme for calculation of atomic charges by the modified Sanderson method and application to some polycyclic organic molecules

Abstract It has been demonstrated that the modified Sanderson formalism (MS) for calculation of atomic charge yields good correlation with C 1s core level shifts in organic molecules with carbon in the sp 3 hybridized state (Sastry, J. Electron. Spectrosc., 85 (1997) 167) as well as in monocyclic aromatic molecules (Patil et al., J. Electron Spectrosc., 85 (1997) 249). In this communication, a reinterpretation of the MS method is presented which leads to an extension of the scheme enabling application to polycyclic molecules for the first time. A linear relationship is established between partial charges on carbon and C 1s core level shifts in some polycyclic organic molecules.

Macromodel—an integrated software system for modeling organic and bioorganic molecules using molecular mechanics

AbstractAn integrated molecular modeling system for designing and studying organic and bioorganic molecules and their molecular complexes using molecular mechanics is described. The graphically controlled, atom‐based system allows the construction, display and manipulation of molecules and complexes having as many as 10,000 atoms and provides interactive, state‐of‐the‐art molecular mechanics on any subset of up to 1,000 atoms. The system semiautomates the graphical construction and analysis of complex structures ranging from polycyclic organic molecules to biopolymers to mixed molecular complexes. We have placed emphasis on providing effective searches of conformational space by a number of different methods and on highly optimized molecular mechanics energy calculations using widely used force fields which are supplied as external files. Little experience is required to operate the system effectively and even novices can use it to carry out sophisticated modeling operations. The software has been designed to run on Digital Equipment Corporation VAX computers interfaced to a variety of graphics devices ranging from inexpensive monochrome terminals to the sophisticated graphics displays of the Evans & Sutherland PS300 series.