1,4‐Phenylene and 2,5‐Thienylene π‐Linkers in Charge‐Transfer Chromophores

Fifteen model charge‐transfer chromophores with ferrocene donors, NO2 acceptors, and 1,4‐phenylene and 2,5‐thienylene π‐linkers were synthesized and their properties investigated by X‐ray analysis, electrochemistry, absorption spectra, and DFT calculations. Structure–property relationships were further evaluated to answer the question of suitability of the π‐linkers in the construction of chromophore backbone. Gradual replacement of 1,4‐phenylene with 2,5‐thienylene and π‐linker extension resulted in a lower HOMO–LUMO gap, a bathochromic shift of both charge‐transfer bands, and overall planarization of the molecule. Hence, thiophene, when incorporated into a chromophore backbone, is a more polarizable moiety that allows very efficient intramolecular charge transfer.