Electronic spectral and photophysical properties of some p-phenylenevinylene oligomers in solution and thin films

Abstract

A comprehensive photophysical and spectroscopic study of a new class of p-phenylenevinylene oligomers (PPV-trimers) possessing different alkyl and alkyloxy sidechain substituents and different end groups (aldehyde, C@C, phenylene and anthracene units) was undertaken in solution at room temperature (293 K), low temperature (77 K) and in thin films. The study comprises absorption, emission and triplet-triplet absorption spectra, together with quantitative measurements of quantum yields (fluorescence, intersystem crossing, internal conversion and singlet oxygen formation) and lifetimes. The data allow the determination of rate constants for all decay processes. From these, several conclusions could be drawn. Changing from alkyl to alkyloxy substituents does not change fluorescence and internal conversion yields but decreases the (already small) intersystem crossing yield. The introduction of anthracene at the terminal ends of the PPV-trimers leads to the lowest fluorescence yield reported in this study. Of particular importance is the fact that the fluorescence quantum yields in films are of the same order of magnitude as those in solution, which suggests the potential for use of these oligomers for light-emitting device applications. With one of the alkyloxy derivatives, a more detailed study of the early part of the fluorescence decay was made, and it was found that upon excitation a fast conformational relaxation process of the initially excited oligomer occurs, leading to a more planar conjugation segment.

Picosecond Structural Relaxation of Abietic Acid Based Amine End Capped Para‐Phenylenevinylene Trimers in Solution

“…The fluorescence spectra exhibit vibrational structure similar to that show by the trimers [14] and the related MEH-PPV polymer. [15] Slight differences in the emission wavelength can be Table 1.…”

“…MBOPV3 438 [11] 493 [11] 0.72 [14] 1.54 [11] 0 [11] 496 [11] 0.71 [14] 1.54 [11] 0 [a] Major component (> 90 %) from triexponential decays (see Figure 3 and Table 2) Figure 2. Normalized absorption spectra of the amines used as end-groups in the AECPV3 studied, in MCH at 293 K, and the fluorescence spectrum of the styryl-phenyl amine, with excitation at 370 nm.…”

Conformational Relaxation of p‐Phenylenevinylene Trimers in Solution Studied by Picosecond Time‐Resolved Fluorescence

“…However, as recently shown, the apparently single-exponential decays of PV oligomers obtained with nanosecond resolution are in fact triple-exponential when measured with picosecond resolution at the appropriate emission wavelengths. [3] The longest decay time is the lifetime of the trimer; the shortest decay time is clearly associated to a dynamic (viscosity and temperature-dependent) process, while the intermediate decay time (independent of solvent viscosity and temperature) is not, and may result from the residual emission of cis isomers.…”

Photodynamics of a PV Trimer in High‐Viscosity Solvents and in PMMA Films: A New Insight into Energy Transfer versus Conformational Relaxation in Conjugated Polymers

“…[4,5] Complexity results from photophysical processes, which in dilute solution include solvent and/or conformational relaxation [3,[6][7][8][9][10] and intrachain energy transfer, [11][12][13] while in concentrated solution or in films they may also involve interchain energy transfer, [2] excimer formation [14] and formation of H or J aggregates. [15][16][17] The correct interpretation of this information is important for detecting, understanding and resolving problems such as imbalance of electron and hole injection currents, [18][19][20][21][22][23] decreased luminescence yields, which result from aggregation quenching that is dependent on the polymer concentration, [15][16][17] and chemical stability of the films.…”

“…Luminescent conjugated organic polymers designed for applications in optoelectronic materials generally show complex fluorescence decays both in solution [1][2][3] and in films. [4,5] Complexity results from photophysical processes, which in dilute solution include solvent and/or conformational relaxation [3,[6][7][8][9][10] and intrachain energy transfer, [11][12][13] while in concentrated solution or in films they may also involve interchain energy transfer, [2] excimer formation [14] and formation of H or J aggregates.…”