CT Fluorescence And Molecular Aggregation Of A Polyimide As Function Of Imidization Condition.

1991 ◽  
Vol 227 ◽  
Author(s):  
M. Hasegawa ◽  
H. Arai ◽  
K. Horie ◽  
R. Yokota ◽  
I. Mita
Keyword(s):  
Fluorescence Spectra ◽  
Intramolecular Charge Transfer ◽  
Amic Acid ◽  
Polymer Chains ◽  
Molecular Aggregation ◽  
Absorption And Fluorescence Spectra ◽  
Model Compounds ◽  
Higher Temperature ◽  
Biphenyltetracarboxylic Dianhydride ◽  
Monomer Fluorescence

ABSTRACTThe emission mechanisms of solid PI(BPDA/PDA) derived from biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA) were examined with the absorption and fluorescence. spectra of model compounds (denoted by M). M(BPDA/CHA) (CHA: cyclohexyl amine) fluoresces at ca. 430 nm in hexafluoro-2-propanol(HFP) solution, while M(BPDA/AN) (AN: aniline) does not. PI(BPDA/PDA) film does not show the monomer fluorescence of biphenyldiimide unit, but shows only intermolecular CT fluorescence peaking at 530–540 nm. This suggests that for PI(BPDA/PDA) film and PI(BPDA/AN) in solution the local excited state of biphenyldiimide units is deactivated owing to intramolecular charge-transfer(CT).The intermolecular CT fluorescence reflecting sensitively molecular packing of PI chains was used to monitor isothermal imidization process of poly(amic acid)(PAA) of BPDA/PDA. The fluorescence of PAA(BPDA/PDA) peaking at 490 nm decreases rapidly and disappears at 30–40% conversion, then the fluorescence of PI(BPDA/PDA) peaking at 540 nm increases gradually during isothermal imidization. The fluorescence intensity at 540 nm increases rapidly as imidization proceeds when imidized at higher temperature. A kinetic study on isothermal imidization shows that the vitrification is strongly related to the reorientation of polymer chains and the final PI structures.

Intramolecular excimer fluorescence from folded ground state rotamers of N,N'dimethyl-N,N'-dipyrenylurea protophanes

2003 ◽  
Vol 81 (6) ◽  
pp. 770-776 ◽  
Author(s):  
Frederick D Lewis ◽  
Todd L Kurth
Keyword(s):  
Ground State ◽  
Fluorescence Spectra ◽  
Fluid Solution ◽  
Absorption And Fluorescence Spectra ◽  
Model Compounds ◽  
Excimer Fluorescence ◽  
Decay Times ◽  
Intramolecular Excimer ◽  
Rotational Equilibrium ◽  
Monomer Fluorescence

The molecular structure, absorption, and fluorescence spectra of N,N'-dimethyl-N,N'-di-1-pyrenylurea and N,N'-dimethyl-N,N'-di-2-pyrenylurea have been investigated and compared to the properties of N,N,N'-trimethyl-N'-pyrenylurea model compounds. Di-1-pyrenylurea exists as a mixture of folded (E,E) syn- and anti-rotamers that interconvert via flipping of one of the pyrene rings to an unfolded (E,Z) rotamer geometry. The symmetric di-2-pyrenylurea exists as a single folded (E,E) conformation which is in equilibrium with a less-stable, unfolded (E,Z) rotamer. The absorption and fluorescence spectra of the dipyrenylureas at 77 K in a rigid glass are similar to those of monopyrenylurea model compounds. However, in fluid solution, the dipyrenylureas exhibit excimer fluorescence and very weak monomer fluorescence which have identical decay times. This behavior is attributed to fast rotational equilibrium between folded rotamers which exhibit excimer fluorescence and unfolded rotamers which exhibit monomer fluorescence. The behavior of the dipyrenylureas is compared with that of other systems that form intramolecular pyrene excimers and diarylureas.Key words: excited state rotamers, dipyrenylureas, pyrene excimers, ureaphane.

Die Medienabhängigkeit der spektralen Lage der Fluoreszenzbande von Indol und substituierten Indolen / The Influence of Environment on the Fluorescence Spectra of Indole and Substituted Indoles

1974 ◽  
Vol 29 (1) ◽  
pp. 84-94
Author(s):  
A. Kawski ◽  
J. Czajko
Keyword(s):  
Excited State ◽  
Electrostatic Interactions ◽  
Fluorescence Spectra ◽  
Effective Dielectric Constant ◽  
Absorption And Fluorescence Spectra ◽  
Model Compounds ◽  
Solvent Shift ◽  
Different Temperatures ◽  
Solvent Molecules ◽  
Degree Of Filling

To gain information about the nature of the microenvironment of tryptophane residues in proteins, the absorption and fluorescence spectra of such model compounds as indole,- 1,2-dimethylindole, and 2-phenylindole were examined in n-heptane -n-butanol mixtures at different temperatures (20, 80 and 120 °C ). Anomalously large red shifts in the fluorescence bands of these compounds at different n-butanol concentrations in n-heptane indicate that the added n-butanol molecules are concentrated around the solute molecules by electrostatic interactions. The red shift is due to the marked increase in the dipole moment of the excited state and to the number of n-butanol molecules in the solvent shell which can reorient themselves during the lifetime of the excited state of the solute molecule. From the spectroscopic data, making use of the “solvent-shift” theory and the statistical model of Mazurenko, the effective dielectric constant of the microenvironment, the average degree of filling up the solvent shell with n-butanol molecules, the average coordination number and the average interaction energy of the solute with the solvent molecules in the ground and excited state, were calculated.

A phthalocyanine-based fluorescent sensor for Zn2+ ion

2013 ◽  
Vol 17 (01n02) ◽  
pp. 99-103 ◽  
Author(s):  
Hui He ◽  
Jian-Yong Liu ◽  
Dennis K.P. Ng
Keyword(s):  
Metal Ions ◽  
Spectral Properties ◽  
Fluorescence Spectra ◽  
Near Infrared ◽  
Fluorescent Sensor ◽  
High Sensitivity ◽  
Absorption And Fluorescence Spectra

This paper describes the preparation and spectral properties of a near-infrared fluorophore in which two bis(2-picolyl)amino moieties are axially linked to a silicon(IV) phthalocyanine core. The effects of various metal ions on its absorption and fluorescence spectra have been examined. The results indicate that this compound shows a high sensitivity and moderate selectivity toward Zn2+ ion.

Influence of Si-Al-Ge-Sb Matricies on Tm3+ Excitation Levels

2008 ◽  
Vol 587-588 ◽  
pp. 293-297
Author(s):  
M. Pospíšilová ◽  
P. Adámek ◽  
P. Peterka ◽  
V. Kubeček ◽  
I. Kašík ◽  
...  
Keyword(s):  
Genetic Algorithm ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Fluorescence Spectra ◽  
Chemical Vapor ◽  
Oscillator Strengths ◽  
Absorption And Fluorescence Spectra ◽  
Measured Absorption ◽  
Optical Fiber Drawing ◽  
Solution Doping

Absorption and fluorescence spectra in the range from 350 to 1750 nm of several Tm3+- doped optical performs (rods) for optical fiber drawing were measured. Silica-based matrices of Al2O3-GeO2-P2O5-Sb2O3-SiO2 composition doped with several thousands ppm of Tm3+ were characterized. The preforms were fabricated by the Modified Chemical Vapor Deposition and by the solution doping methods. A new method, Genetic Algorithm SPEctra Decomposition was adopted for processing of the measured absorption spectra. This decomposition made it possible to calculate the oscillator strengths of Tm3+ absorption levels. Fluorescence bands of Tm3+ at 800 nm or 1640 nm were found in fluorescence spectra measured on the preform samples when excited at 1064 nm only.

In situ Raman Spectroscopic Observation of Polymer Chains in Semi-Crystalline Polyethylene Solids

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Yusuke Hiejima ◽  
Takumitsu Kida ◽  
Koh-hei Nitta
Keyword(s):  
Conformational Changes ◽  
Tensile Elongation ◽  
Spectroscopic Observation ◽  
Polymer Chains ◽  
Trans Conformation ◽  
Raman Spectroscopic ◽  
Higher Temperature ◽  
Microscopic Origin ◽  
Crystalline Polyethylene

AbstractIn situ Raman spectroscopy is applied for polyethylene solid under various environments to elucidate the morphological and conformational changes. The trans conformation retains up to higher temperature for high-density polyethylene, reflecting higher stability of the orthorhombic crystals composed of stacked trans chains. It is suggested that the conversion of the non-crystalline trans chains to the crystalline phase is the microscopic origin of thermal history in the crystallinity, whereas the transformation between the trans and gauche conformers is practically in thermal equilibrium. Microscopic and dynamic mechanism of deformation during uniaxial stretching is investigated for the molecular orientation and the microscopic load sharing on the crystalline and amorphous chains. Lower crystallinity results in smoother and higher orientation toward the stretching direction, as well as higher load on the amorphous chains, during tensile elongation.

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