NIR-absorbing TCBD and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD bridged derivatives of 1,1′-bis(N,N-dimethylaniline)-substituted ferrocene.

• Designed and synthesized push-pull chromophores 3–8 through Pd-catalyzed reactions and cycloaddition-retro-electrocyclization with TCNE and TCNQ. • Achieved a second-time reaction with 1,1′-dialkynylferrocenes and TCNE/TCNQ, previously challenging. TCNQ-based derivatives exhibit red-shifted absorption compared to TCNE-based ones. • Acceptors red-shift absorption and reduce the HOMO-LUMO gap and studied the influence of conjugation length and acceptor strength on photophysical and electrochemical properties. Symmetrical and unsymmetrical donor-acceptor (D–A) based chromophores were designed and synthesized by the Pd–catalyzed Sonogashira cross–coupling reaction of 1,1′-diiodoferrocene with (4- N,N -dimethylaminophenyl)ethyne followed by [2+2] cycloaddition-retroelectrocyclization reaction with tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ). Ferrocene was used as a central donor unit and 4-(N,N -dimethylamino)phenyl group as the end-capping donor. Herein, we report the cycloaddition-retrocyclization reaction of TCNE/TCNQ groups on the disubstituted ferrocene containing more than one triple bond to get disubstituted tetracyanobutadiene (TCBD) and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD products. The effect of the conjugation length and different π–acceptor linkers were investigated by photophysical, redox and computational studies. The redox study reveals multiple oxidation waves corresponding to donor moieties (ferrocene and 4-(N,N -dimethylamino)phenyl group) and reduction waves corresponding to acceptor units (TCBD / cyclohexa-2,5- diene-1,4-diylidene-expanded TCBD). The thermogravimetric analysis data shows that the compounds exhibit high thermal stability. The computational studies reveal HOMO-LUMO gaps consistent with the experimentally obtained data. [Display omitted] [ABSTRACT FROM AUTHOR]

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