Fluorescence depolarization in poly(p-phenylphenylenevinylene) and related oligomers

Abstract

The photophysical behavior of poly (p-phenylphenylenevinylene) (PPPV) and several oligomeric model compounds in isotropic and anisotropic samples is investigated by means of polarized fluorescence spectroscopy. As long as excitation energy transfer and mutual alignment are considered, the behavior of PPPV can be modeled by a chain consisting of a distribution of independent oligomeric segments. The results of fluorescence polarization, e.g., the nonzero value of r in isotropic PPPV, cast doubt on the application of the semiconductor band model but favor an interpretation of spectroscopic properties in terms of molecular transitions. The orientation coefficients of the oligomers and of PPP V in stretched polyethylene are determined.The change of fluorescence spectra of oriented PPPV in stretched polyethylene demonstrates directly that conformational changes of the macromolecule influence the pathway of energy transfer.

Synthesis of Compounds for Los Alamos National Laboratory

“…This difference in bettavior has-been observed before where substituents on the para-position of phenyl radicals of DSB, regardless of their electronic structure, cause a more significant bathochromic shift in the spectrum than substituents in meta-or ortho-positions {41 ]. The excitation spectra of compounds I-VI in solution coincide with their absorption spectra, as has been similarly observed in other systems [35,36].Figs. 3-5 show the fluorescence, excitation and emission spectra for films of DSB on quartz prepared by thermal vacuum deposition, as well as spectra of solid solutions of DSB in PMMA with concentrations of 49 and 0.9%, respectively.…”

“…An analysis of the published data concerning the formation of excimer-like molecular dimers in films obtained by depositing the chromophore onto a substrate [26][27][28] and in polymer media [29][30][31][32][33][34] shows that information on the optical properties of such aggregates in DBS-based systems is very limited. In recent publications [35,36] possible aggregations of tert-butyl-substituted DSB in a polystyrene matrix (solid solution) and phosphonate-substituted DSB in a dimethylsulfoxide solution were discussed.…”

“…In various studies, the latter have been designated as sandwich dimers [ 19,20] by depositing the chromophore onto a substrate [26][27][28] and in polymer media [29][30][31][32][33][34] shows that information on the optical properties of such aggregates in DBS-based systems is very limited. In recent publications [35,36] possible aggregations of tert-butyl-substituted DSB in a polystyrene matrix (solid solution) and phosphonate-substituted DSB in a dimethylsulfoxide solution were discussed.In this work, we report the absorbance, excitation and fluorescence spectra of oligomeric systems I-VI and compare these with spectra of MEHPPV (VII) and the dialkoxy PPVS (VIII-X) (Scheme 1). The capacity to form excimer-like molecular dimers for some of these compounds was also determined.…”

“…The results could be explained by either of two phenomena (a) the existence of fluorescent aggregates and/or (b) excitation energy transfer from the absorbing segment of the polymer to the longest and therefore energetically lowest segment on each chain prior to emission. The second mechanism has been used [35 ] to explain the dependence of the fluorescence excitation spectra on the wavelength of emission for solutions of poly (p-phenylphenylenevinylene) in toluene. The red shift of the emission maximum for films of polymers VII and VIII in comparison with the emission maximum for solutions of these polymers maybe attributed to a more efficient energy transfer processes in the films.…”

Polarized optical spectroscopy applied to investigate two poly(phenylene-vinylene) polymers with different side chain structures

“…45 Calculating the luminescence anisotropy for ordered systems is not possible as the value of the denominator, F VVV +2GF VVH , does not reflect the total intensity, which in turn makes normalization impossible. 45,46 The dichroic ratio for the LEPs dispersed in the LCs is calculated at the luminescence maximum ͑575 nm͒, returning a value of 2.55 for MEH-PPV, while OC 1 C 10 -PPV/ BL001 returned a value of 1.45. In comparing the dichroic ratio of the two LEP systems, we note that the data are in conjunction with the LD data which also revealed a higher degree of alignment relative to the orientation direction for MEH-PPV as compared to OC 1 C 10 -PPV.…”