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Fluorescence/photoisomerization competition in trans-aza-1,2-diarylethenes

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Abstract

The effect of the presence and position of the nitrogen heteroatom on the photobehaviour of a series of symmetric and asymmetric 1,2-diarylethenes, where one or both the one-, two- or three-membered aryl groups, linked to the ethene bridge, contain(s) nitrogen heteroatoms, has been investigated by fluorimetric and photochemical techniques. The yield of the radiative pathway is generally reduced with respect to the corresponding hydrocarbons, due to a smaller energy barrier for trans→cis (E→Z) photoisomerization in the singlet state, which often can be slightly favoured in the aza-compounds. All compounds investigated exist in solution as mixtures of two or more conformers, which can have different spectral and kinetic properties. Attempts to separate the intrinsic properties by selective photoexcitation, at a wavelength where the light is mainly absorbed by one conformer, allowed in some favourable cases the spectra and decay times of the largely prevalent (quasi-pure) conformer to be obtained. In two cases, the formation of intramolecular (hydrogen-bond-type) interactions between the nitrogen atom and the nearest hydrogen atom of the ethene bridge (proved by NMR measurements and confirmed by theoretical calculations) were found to stabilize a specific conformer thus affecting a selective relaxation of the excited molecule.

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Acknowledgements

The authors are grateful to Dr. Elena Marri for her assistance in the first part of this research and to Mr. Danilo Pannacci for his skilful technical collaboration in the HPLC measurements.

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Authors and Affiliations

  1. Dipartimento di Chimica and Centro di Eccellenza Materiali Innovativi Nanostrutturati (CEMIN), Università di Perugia, 06123, Perugia, Italy

    S. Ciorba, G. Ciancaleoni, U. Mazzucato & A. Spalletti

  2. Dipartimento di Ingegneria Industriale, Università di Bergamo, 24044, Dalmine (Bergamo), Italy

    F. Fontana & T. Caronna

Authors
  1. S. Ciorba
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  2. F. Fontana
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  3. G. Ciancaleoni
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  4. T. Caronna
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  5. U. Mazzucato
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  6. A. Spalletti
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Correspondence to A. Spalletti.

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Table SI 1

Calculated spectral properties (λ and f), heats of formation \(\left( {\Delta H_f^0 } \right)\) and dipole moment (μ) for the rotamers of the EE isomer of the investigated compounds. (DOC 37 KB)

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Ciorba, S., Fontana, F., Ciancaleoni, G. et al. Fluorescence/photoisomerization competition in trans-aza-1,2-diarylethenes. J Fluoresc 19, 759–768 (2009). https://doi.org/10.1007/s10895-009-0472-0

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  • DOI: https://doi.org/10.1007/s10895-009-0472-0

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