Heiner Detert

Di(p‐aminostyryl)pyrazines with voluminous substituents on the nitrogen and in the adjacent positions were prepared via twofold aldol condensation. Absorption and emission spectra are influenced by increasing steric hindrance because the orbital overlap between nitrogen and π‐system is modulated by voluminous groups. Strong solvatochromism of the fluorescence and huge Stokes shifts result from amplified donor–acceptor interaction in the excited state. Protonation occurs at the terminal amino groups first, followed by protonation of the central pyrazine. With increasing strength of acid, absorption and emission spectra are first shifted to the blue followed by a redshift. Copyright © 2012 John Wiley & Sons, Ltd.

Oligo(phenylenevinylene)s (OPV) with a 2,5‐diaminobenzene centre were prepared via twofold Horner olefinations of substituted terephthalaldehydes. Whereas variations of the environment only slightly alter the electronic excitation spectra, the fluorescence spectra appear to be highly responsive. Besides a positive solvatochromism, the emission is very sensitive towards protonation. Quenching or appearance of new emitting species depends on the substitution pattern and is controlled by the concentration of the acid. Very large Stokes shifts indicate extensive structural changes in the excited states. Copyright © 2006 John Wiley & Sons, Ltd.

The electronic spectra of oligo(phenylenevinylene)s with five benzene rings and an acceptor–donor–acceptor substitution pattern were investigated. Although the absorption spectra are mostly unaffected by an increasing solvent polarity, both bathochromic shifts and reduced efficiencies of the fluorescence arise with the quadrupolar electronic structure. The chromophores with the lowest oxidation or reduction potentials are the most sensitive towards the environment. The synthesis of the centrosymmetrical oligomers was performed in a sequence of two two‐fold Wittig–Horner olefinations. Copyright © 2004 John Wiley & Sons, Ltd.

A series of C₂‐symmetrical aza‐analogous 1,4‐distyrylbenzenes were synthesised via two‐fold PO‐activated olefinations or Heck reactions. Pyridine, pyrimidine and quinoline were used as terminal rings, and the 2,5‐positions of the central benzene ring were substituted with H, alkoxy, or alkylsulfonyl groups. These strongly fluorescent compounds are freely soluble in common solvents such as toluene or chloroform. Whereas the electronic spectra of the pyridine and pyrimidine chromophores were very similar to those of the parent compound 1,4‐distyrylbenzene, the spectra of the former were altered considerably in the presence of trifluoroacetic acid. Depending on the concentration of the acid, protonation of the ground state and/or the excited state caused bathochromic shifts of the absorption and the emission spectra, accompanied by reductions in the fluorescence efficiencies. Copyright © 2004 John Wiley & Sons, Ltd.