Cross-Conjugation versus Linear Conjugation in Donor-Bridge-Acceptor Nitrophenol Chromophores

European Journal Of Organic Chemistry 2014, 2044 - 2052 (2014)

Cross-Conjugation versus Linear Conjugation in Donor-Bridge-Acceptor Nitrophenol Chromophores

M.A. Christensen, E. A. Della Pia, J. Houmøller, S. Thomsen, M. Wanko, A. D. Bond, A. Rubio, S. Brøndsted Nielsen, M. Brøndsted Nielsen

The influence of cross-conjugation vs. linear conjugation for the electronic communication between donor and acceptor groups in phenol(ate)-bridge-nitrobenzene chromophores was investigated by solution and gas-phase absorption spectroscopies, fluorescence spectroscopy, and by quantum chemical calculations. Compounds subject of study include among others geminally- and trans- substituted diethynylethenes prepared by stepwise Sonogashira cross-coupling reactions as well as the cross-conjugated analogue of stilbene. A butadiyne-bridged donor-acceptor chromophore was prepared by an unsymmetrical Pd-catalyzed coupling between a chloroalkyne and a terminal alkyne. While the linearly conjugated chromophores exhibited a strong and redshifted charge-transfer (CT) absorption maximum upon deprotonation in solution, a new redshifted absorption was either absent or present as a weak shoulder for the cross-conjugated derivatives.

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We gratefully acknowledge John C.Tully and Xavier Oriols for useful conversations. GA acknowledges the Beatriu the Pinós program for financial support through the project 2010BP-A00069.IF thanks the Alexander von Humboldt Foundation for financial support.AR acknowledges support by European Research Council Advanced Grant Dynamo (ERC-2010-AdG-267374), Spanish Grant (FIS2010-21282-C02-01),Grupos Consolidados UPV/EHU del Gobierno Vasco (IT 578-13). Ikerbasque and European Commission project CRONOS (Grant number 280879-2)

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