Synthesis, crystal structure and photophysical properties of 5-mono- and 5,9-bis-(arylethynyl)-functionalized pyrenes

7-tert-Butyl-1,3-dimethylpyrene 5-carbaldehyde and 7-tert-butyl-1,3- dimethylpyrene 5,9-dicarbaldehyde were converted to the corresponding (4-methoxyphenylethynyl)pyrenes by the Wittig reaction with 4-methoxyphenyl methyl phosphonium ylide followed by bromination and dehydrobromination. Single-crystal X-ray analysis of 7-tert-butyl-5-(4-methoxyphenylethynyl)-1,3- dimethylpyrene revealed that there is a 1-D, slipped, face-to-face motif with off-set, head-to-tail stacked columns, which are clearly influenced by the single, bulky, tert-butyl group in the pyrene ring at the 7-position. Detailed studies on photophysical properties and electrochemical characteristics in solutions strongly indicate that they might be promising candidates for organic optoelectronic applications, such as organic light-emitting devices (OLEDs) or as models for investigating the fluorescent structure-property relationship of the alkynyl-functionalized pyrene derivatives.