Thiophene ring-fragmentation reactions: Principles and scale-up towards NLO materials

A systematic study on the thiophene ring-fragmentation (TRF) reaction, yielding the Z-isomer of ene-yne type compounds, is presented. The investigations focus on the origins and pathways of potential side-reactions, resulting in an advanced synthetic protocol featuring enhanced selectivity and efficiency. The fragmentation threshold temperatures as well as reaction kinetics have been investigated utilizing inline infrared spectroscopy revealing unexpected results particularly concerning the reaction order (zero-order process). With regard to safety, selectivity, and up-scaling a flow-chemistry procedure for the TRF reaction has been developed. Finally, the technological relevance of the ene-yne structural motif is extended by a new design concept for NLO-chromophores showing the highest second harmonic generation efficiencies reported for these scaffolds.

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