R. Goedeweeck

SOLVENT EFFECTS ON INTRAMOLECULAR EXCIMER FORMATION IN N-ACETYL-BIS(PYRENYLALANINE)-METHYLESTER

Abstract— The synthesis, absorption and emission properties of threo and erythro N‐acetyl‐bis‐(pyrenylalanine)‐methylester are discussed. The intensity of excimer emission is very dependent on the tendency of the solvent to interact with the peptide function by hydrogen bonding. Hydrogen accepting solvents shift the equilibrium between the different conformations, adopted by these dipeptides, towards a random coil conformation, which is unfavourable for excimer formation. In strongly hydrogen donating solvents however, a very intense excimer emission is observed due to a reduction of the partial double bond character of the peptide bond by an hydrogen bridge with the solvent molecules.

Intramolecular formation and properties of exciplexes in α-Aryl-ω-N,N-dialkylaminoalkanes

Abstract Fluorescence properties of intramolecular exciplexes in α-aryl-ω-N,N-dialkylaminoalkanes, with aryl equal to phenyl. 1-naphthyl, 2-naphthyl and pyrenyl, are compared with calculated ones on the basis of a semi-empirical model. The importance of the difference in the coulombic term in this series is stressed. Optimum geometries for the exciplex structure are proposed.

Fluorescence Probing of the Local Dynamics of Polymers: A Model Approach

The importance of the ground state configurational distribution of a polymer chain in solution in relation to its physical properties has been well recognized. Differences in the photophysical properties of polymers with different tacticity have been noted in the past. However, an in depth study of the relation between the configurational distribution and polymer photophysics is still, in view of the complexity of the possible relaxation pathways in a polymer system, a difficult task.

Chiral discrimination in the intermolecular excimer formation of N-acetyl-1-pyrenylalanine methyl ester in chiral solvents

Abstract Intermolecular excimer formation of both optically active enantiomers of N -acetyl-1-pyrenylalanine methyl ester was studied by stationary (fluorescence spectroscopy) and transient (time-correlated single-photon counting) techniques in two chiral solvents: (+)-2-octanol and (+)-2-chloropropionate methyl ester. The excimer formation of the l isomer is 15% more efficient than that of the d isomer in both solvents at room temperature. This chiral discrimination is higher at low temperatures and a discrimination energy of 300 cal mol −1 and 200 cal mol −1 in (+)-2-octanol and (+)-2-chloropropionate methyl ester is reported. Solute—solvent interactions are assumed to contribute to the optical activity of the peptide in chiral media, since the diastereoisomeric [ l and d solute … (+)-solvent] pairs have a different tendency to form the intermolecular excimer.