Substituent

About: Substituent is a research topic. Over the lifetime, 42877 publications have been published within this topic receiving 516716 citations. The topic is also known as: side chain & side group.

Hammett Substituent Constants for Electron-withdrawing Substituents: Dissociation of Phenols, Anilinium Ions and Dimethylanilinium Ions

Abstract: In order to gain more information concerning the a-constant, the thermodynamic pK values, in water a t 25\", of a number of substituted phenols, dimethylanilines and anilines have been measured. Discussion of substituent constants is concerned primarily with the p-NOz, p-CN, 3,4-C4H4 and p-NO groups. The reaction constant for dimethylanilinium ion dissociation has been obtained and an explanation has been offered for differences noted between this series and the anilinium ion series.

Sidewall Functionalization of Single-Walled Carbon Nanotubes with Nitrile Imines. Electron Transfer from the Substituent to the Carbon Nanotube

Abstract: A new, versatile methodology for functionalization of single-walled carbon nanotubes (SWNTs), using 1,3-dipolar cycloaddition of nitrile imines to the sidewalls of SWNTs has been used to synthesize two soluble, photoactive single walled carbon nanotubes containing n-pentyl esters at the tips and 2,5-diarylpyrazoline units at the walls of the tubes. The success of the synthesis has been demonstrated by solution 1H and 19F NMR as well as UV−vis and FT-IR spectroscopy. These two compounds have been selected to have soluble single wall carbon nanotubes substituted either with an electron-poor 3,5-bis(trifluoromethyl)phenyl or electron-rich 4-(N,N-dimethylamino)phenyl on the C atom of the pyrazoline ring. Laser flash photolysis in dynamic flow of these carbon nanotubes in acetonitrile reveals the formation of several transient species decaying in the microsecond time scale. All the available data, including the photochemistry of model compounds, quenching experiments with electron donors and acceptors, and inf...

Ultraviolet absorption polymer comprising specific substituent and based on 2'-hydroxyphenyl benztriazole and photographic element containing it

Abstract: PROBLEM TO BE SOLVED: To provide a photographic element having large specific resistance against light, good stability of dyes in an image and showing low density of optical induced yellow discoloration, by incorporating a specified polymer UV- absorbent. SOLUTION: This photographic element contains a photosensitive part and an UV-absorbing polymer. The UV-absorbing polymer contains repeating units of 2'-hydroxyphenyl benzotriazole having substituents in 5- or 6-position selected from halogen, cyano, carboxyl or sulfonyl groups, and 4'-alkoxy groups bonded to the polymer chain. The alkylene part of the alkoxy group consists of, successively, a first bivalent connecting group, then an oxygen, sulfur or amino group, and a second bivalent connecting group bonded to the polymer chain (however, it has no substituent in the 3'-position and does not have any of -NH-, -OH and -SH in the 4'-position).

Spectral properties of substituted coumarins in solution and polymer matrices.

Abstract: The absorption and fluorescence spectra of substituted coumarins (2-oxo-2H-chromenes) were investigated in solvents and in polymer matrices. The substitutions involved were: (1) by groups with varying electron donating ability such as CH3, OCH3 and N(CH3)2, mainly, but not exclusively, in positions 7 and (2), by either CHO or 4-PhNHCONHN=CH- in position 3. While the spectra of non-substituted coumarin-3-carbaldehyde has absorptions at approximately 305 and 350 nm, substitution at position 7 leads to remarkable changes in the shape of the absorption spectrum and shifts the absorption to a longer wavelength. Similarly, the replacement of the formyl group with a semicarbazide group substantially influences the shape of the absorption spectrum, and coumarins which have only N(CH3)2 in position 7 experience small changes. These changes are associated with the increasing intramolecular charge transfer (ICT) character and increasing conjugation length of the chromophoric system, respectively, in the studied molecules. The fluorescence is almost negligible for derivatives which have H in this position. With increasing electron donating ability, and the possibility of a positive mesomeric (+M) effect of the substituent in position 7 of the coumarin moiety, the fluorescence increases, and this increase is most intense when N(CH3)2 substitutes in this position, for both 3-substituted derivatives. Spectral measurements of the studied coumarins in polymer matrices revealed that the absorption and fluorescence maxima lay within the maxima for solvents, and that coumarins yield more intense fluorescence in polymer matrices than when they are in solution. The quantum yield of derivatives which have a dimethylamino group in position 7 in polymer matrices approaches 1, and the fluorescence lifetime is within the range of 0.5–4 ns. The high quantum yield of 7-dimethylamino derivatives qualifies them as laser dyes which have kF higher than knr in the given medium. This is caused by stiffening of the coumarin structure in polar polymer matrices, such as PMMA and PVC, due to higher micro-viscosity than in solution and intermolecular dipole-dipole interaction between chromophore (dopant) and matrix.