Untersuchungen zur Konformerenvielfalt von mono- und 2,5-dialkoxysubstituierten Poly(1,4-phenylenethenylen)en

Abstract

Investigations on the Conformational Variety of Mono‐ and 2,5‐Dialkoxy Substituted Poly(1,4‐phenyleneethenylene)s The alkoxy substituted poly(1,4‐phenyleneethenylene)s 1 and 2 can principally exist in an enormous variety of conformers (table 1). However, force field calculations (MMX) reveal a far‐reaching restriction to a relatively small number of non planar conformers with minimized steric energy. The decisive criterion is due to the interaction between the oxygen atoms and the olefinic hydrogens. An increasing steric hindrance should lead to higher twist angles θ in the main chain and hence to a shorter effective conjugation length. Such an effect could play a minor role between the unsubstituted parent compound and 1/2, but UV/Vis‐ and fluorescence spectra don't give any hints for a change of the effective conjugation length n ≈︁ 8 between 1 and 2.

Origin of the Red Sites and Energy Transfer Rates in Single MEH‐PPV Chains at Low Temperature

“…The chromophores' average spatial extent under these conditions is mainly limited by torsion along the polymer backbone. [56,74] Constraints on the conformational flexibility in ordered regions of polymer molecules in the single-molecule samples can significantly reduce these torsional "defects", [56,75] leading to larger conjugation lengths and thus transition energies lowered compared to the polymer limit.…”

“…[56] We suggest that in a MEH-PPV molecule, regions characterised by a significant degree of chain ordering coexist with less ordered parts of the chain. We consider the ordered parts the origin of the red chromophores due to a planarisation which especially limits torsions around the molecular backbone (having been shown to crucially define the extent of p delocalisation [56,74] ) and thus results in larger conjugation lengths. Chain ordering as reason for the red emission is supported by polarisation-resolved excitation spectra, showing that nearly all red chromophores within a single polymer chain adopt a similar orientation.…”

Pentadecamer 2,5-Dipropoxy-1,4-phenylenevinylene

“…The all-(E)-configured, monodisperse compound represents a fully conjugated rod-like molecule. The inherent conformational freedom [20] leads to a calculated length [21] of the chromophore of 99Ϫ102 Å . The UV/Vis absorption band of 1j measured in CHCl 3 has a maximum at λ max ϭ 482 nm and an edge at λ 0.1 ϭ 543 nm.…”

Single-Crystal Structures of Model Compounds for Poly(2,5-dialkoxy-1,4-phenylenevinylene)

“…can be altered over a broad range. [16][17][18][19][20][21] The conformational variety in oligo-and poly(1,4phenylenevinylene)s 22 has on the other hand a decisive influence on the properties. The convergence of the absorption maxima as well as of the fluorescence maxima in the series of oligo(1,4-phenylenevinylene)s such as 1 is essentially determined by conformational effects.…”

“…One way to interpret the properties of poly(1,4phenylenevinylene)s is to study these compounds by means of various force field 22 or quantum mechanical calculations. [24][25][26] A main drawback of theoretical approaches is given by starting geometries which are derived from inappropriate model compounds; (E)- stilbene for example as a model for a substituted PPV is certainly inappropriate.…”