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.

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.

A Highly Resolved Yibronic Spectra of Dioxido-p-terphenyl and Trioxido-p-quaterphenyl in n-Hexanc at 77 K

1982 ◽  
Vol 37 (1) ◽  
pp. 91-94
Author(s):  
A. Kawski ◽  
M. Ligȩza
Keyword(s):  
Raman Spectra ◽  
Ground State ◽  
Fluorescence Spectra ◽  
Vibrational Structure ◽  
Ir And Raman Spectra ◽  
Absorption And Fluorescence Spectra ◽  
Excited Singlet ◽  
Ir And Raman ◽  
Good Agreement

Abstract Highly resolved vibronic absorption and fluorescence spectra of dioxido-p-terphenyl and the fluorescence spec-trum of trioxido-p-quaterphenyl in n-hexane at 77 K were obtained. The analysis of the vibrational structure in the excited singlet Si and in the ground So state gives funda-mental frequencies in the ground state in good agreement with those from infrared (IR) and Raman spectra.

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.

Excimer fluorescence XII. The pyrene crystal excimer interaction potential

1968 ◽  
Vol 304 (1478) ◽  
pp. 291-301 ◽  
Keyword(s):  
Excited State ◽  
Interaction Potential ◽  
Ground State ◽  
Fluorescence Spectra ◽  
Zero Point ◽  
Resonance State ◽  
Intermolecular Potential ◽  
Exciton Resonance ◽  
Point Energy ◽  
Excimer Fluorescence

The excimer fluorescence spectra of pure single pyrene crystals were observed from 4 to 353 °K. The data are analysed to determine the vibrational zero-point energy of the excimer (= 90 cm -1 ), the force constants of the excited state (= 1.93 x 10 5 dyn/cm) and ground state (= 3.25 x 10 5 dyn/cm) of the dimer, and the equilibrium intermolecular separation (= 3.34 Å) of the excimer. The repulsive intermolecular potential, the excimer energy, and the attractive excimer interaction potential, V' = 51330 - 1.136 x 10 6 / r 3 (cm -1 ) are determined as functions of the intermolecular separation r (Å). V' is shown to be consistent with an exciton resonance state originating from the 1 B a state of the pyrene molecule.

Theoretical and Experimental Investigation on Dipole Moment of Synthetized yt-Base in the Ground and Excited States

1979 ◽  
Vol 34 (2) ◽  
pp. 172-175 ◽  
Author(s):  
I. Gryczyński ◽  
Ch. Jung ◽  
A. Kawski ◽  
S. Paszyc ◽  
B. Skalski
Keyword(s):  
Experimental Investigation ◽  
Dipole Moment ◽  
Excited State ◽  
Excited States ◽  
Ground State ◽  
Fluorescence Spectra ◽  
Dipole Moments ◽  
Aprotic Solvents ◽  
Absorption And Fluorescence Spectra ◽  
First Excited State

Abstract The electric dipole moment of yt-Base calculated by the CNDO/S and JNDO/S method is μg = 3.42 D and μg = 3.74 D in the ground state and μe = 4.41 D and μe = 5.67 D in the first excited ππ*-state, respectively, μg and μe being nearly antiparallel. Measurements of absorption and fluorescence spectra of yt-Base in aprotic solvents of different polarity yielded μg = 3.8 D and μe = 4.3 D and the directions of dipole moments were found to be nearly antiparallel.This comparison may be considered as an indication for the ππ* character of the observable first excited state, although the CNDO/S-and JNDO/S-calculations predict a nπ*-state as the lowest lying excited state

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