Pyridines and related hetarenes have been used as electron-deficient subunits in conjugated oligomers and polymers, with applications ranging from electronic materials to supramolecular chemistry. Key features of these rings are the high electon affinity and the ability to interact with protons, Lewis acids and alkylating agents. As part of our interest in donor/acceptor substituted conjugated oligomers we use these heterocycles as acceptors in oligo(phenylenevinylene)s. The quadrupolar electronic structure results in a strongly solvent-depending fluorescence. Additionally, due to the basic heterocycles, the electronic spectra of these chromophores are sensitive to hydrogen bonding. Protonation alters both, absorption and emission spectra. Moreover, the position of the basic centre relative to the conjugated system is controlling the impact of solvent dipoles and, even more pronounced, of protons on the electronic spectra. Depending on the relative basicities of the different sites, multiple changes in the electronic spectra result from increasing concentration or pK_A . These soluble dyes are interesting for sensor technology since different ways of interaction with the environment may result in two different ways of molecular answers (absorption/fluorescence). Furthermore, as these aza-OPVs are characterized by a quadrupolar electronic structure, they are also attractive as two-photon absorbing dyes.

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