Abstract
The acid—base equilibria of three aza-derivatives of EE-1,4-diphenylbutadiene and the excited state properties of their neutral and protonated forms have been studied in aqueous solutions. The prevalent relaxation of the neutral molecules is photoisomerization by a diabatic singlet mechanism accompanied by substantial internal conversion while the quantum yield of the radiative pathway is very small, particularly for the ortho- and para-substituted pyridines. Protonation affects only slightly the isomerization yield of these two compounds while drastically decreasing that of the meta-substituted analogue. Molecular orbital calculations and comparison with the corresponding azastilbenes indicate that the first excited singlet state of the protonated meta compound has a net charge transfer character, which leads to an increase of the torsional barrier in S1. Application of the Förster cycle to the three compounds showed that they become much stronger bases in S1. The 3-pyridyl derivative proved to be peculiar also in this respect since its equilibration with the proton occurs during the S1 lifetime thus allowing the acid–base equilibration in the excited state to be directly monitored by fluorimetric titration.
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U. Mazzucato, Photophysical and photochemical behaviour of stilbene-like molecules and their aza-analogues, Pure Appl. Chem., 1982, 54, 1705–1721 and references therein.
G. Bartocci, U. Mazzucato, F. Masetti and G. Galiazzo, Excited state reactivity of aza-aromatics. 9. Fluorescence and photoisomerization of planar and hindered styrylpyridines, J. Phys. Chem., 1980, 84, 847–851.
F. Barigelletti, S. Dellonte, G. Orlandi, G. Bartocci, F. Masetti and U. Mazzucato, Effect of temperature on the photophysical properties of styrylpyridines, J. Chem. Soc., Faraday Trans. 1, 1984, 80, 1123–1129.
D. G. Whitten and M. T. McCall, Radiationless processes in the photochemistry of stilbazoles and 1,2-bispyridylethylenes, J. Am. Chem. Soc., 1969, 91, 5097–5103.
Y. J. Lee, D. G. Whitten and L. Pedersen, Importance of 1n,π* states in N-heterocycles. Internal conversion, intersystem crossing and isomerization in azastilbenes, J. Am. Chem. Soc., 1971, 93, 6330–6332.
D. G. Whitten and Y. J. Lee, Photoaddition and photoreduction reactions of azastilbenes. Solvent effects on photoreactivity of aza aromatics, J. Am. Chem. Soc., 1972, 94, 9142–9148.
S. C. Shim, M. S. Kim, K. T. Lee, B. M. Jeong and B. H. Lee, Photochemistry of aza-1,2-diarylethylenes, J. Photochem. Photobiol. A, 1992, 65, 121–131 and references therein.
E. J. Shin, E. Y. Bae, S. H. Kim, H. K. Kang and S. C. Shim, Photophysical properties and photoisomerization behaviour of 1-(9-anthryl)-2-(n-pyridyl)ethenes (n = 2, 3 or 4), aza-analogues of 1-(9-anthryl)-2-phenylethene, J. Photochem. Photobiol. A., 1997, 107, 137–146.
G. Marconi, G. Bartocci, U. Mazzucato, A. Spalletti, F. Abbate, L. Angeloni and E. Castellucci, Role of internal conversion on the excited state properties of trans-styrylpyridines, Chem. Phys., 1995, 196, 383–393 and references therein.
G. Marconi, G. Bartocci, U. Mazzucato, A. Spalletti, F. Abbate, L. Angeloni and E. Castellucci, A theoretical and experimental study of the excited state relaxation properties of mono-aza- and di-aza- trans-stilbenes, Am. Inst. Phys., Conf. Proc., 1996, 364, 175–182.
L. Angeloni, E. Castellucci, G. Bartocci, U. Mazzucato, A. Spalletti and G. Marconi, Solvent effect on the photophysics and photochemistry of trans-3-styrylpyridine, Gazz. Chim. Ital., 1996, 126, 609–613.
G. Bartocci, G. Galiazzo, U. Mazzucato and A. Spalletti, Photophysics and photochemistry of the EE and ZE isomers of 1-(n-pyridyl)-4-phenyl-1,3-butadiene (n = 2, 3 and 4), Phys. Chem. Chem. Phys., 2001, 3, 379–386.
W. A. Yee, S. J. Hug and D. S. Kliger, Direct and sensitized photoisomerization of 1,4-diphenylbutadienes, J. Am. Chem. Soc., 1988, 110, 2164–2169.
G. Cauzzo, G. Galiazzo, U. Mazzucato and N. Mongiat, Acid-base equilibria of isomeric styrylpyridines and some of their derivatives. Spectrophotometric study, Tetrahedron, 1966, 22, 589–593.
G. Favaro, U. Mazzucato and F. Masetti, Excited state reactivity of aza-aromatics. I. Basicity of 3-styrylpyridines in the first excited singlet state, J. Phys. Chem., 1973, 77, 601–604.
G. Bartocci, P. Bortolus and U. Mazzucato, Excited state reactivity of aza-aromatics. II. Solvent and protonation effects on photoisomerization and luminescence of styrylpyridines, J. Phys. Chem., 1973, 77, 605–610.
P. Bortolus, G. Cauzzo, U. Mazzucato and G. Galiazzo, Cis-trans photoisomerization of styrylpyridines, Z. Phys. Chem. Neue Folge, 1966, 51, 264–273.
U. Mazzucato, F. Masetti and G. Favaro, Excited state reactivity of aza-aromatics. V. Proton transfer from the solvent to aza-aromatics in the excited state, Gazz. Chim. Ital., 1975, 105, 1177–1185.
H. Meier, The photochemistry of stilbenoid compounds and their role in materials technology, Angew. Chem., Int. Ed. Engl., 1992, 31, 1399–1540.
P. Gajdek, R. S. Becker, F. Elisei, U. Mazzucato and A. Spalletti, Excited state behaviour of some trans-stilbene analogues bearing thiophene rings, J. Photochem. Photobiol., A, 1996, 100, 57–64.
E. F. G. Herington, Applications of the electronic spectra of pyridine homologs to quantitative analysis and to the measurement of dissociation constants, Discuss. Faraday Soc., 1950, 9, 26–34.
J. H. Pinckard, B. Wille and L. Zechmeister, A comparative study of the three stereoisomeric 1,4-diphenylbutadienes, J. Am. Chem. Soc., 1948, 70, 1938–1944.
I. Baraldi, A. Spalletti and D. Vanossi, Rotamerism and electronic spectra of aza-derivatives of stilbene and diphenylbutadiene. A combined experimental and theoretical study, Spectrochim. Acta Part A, 2003, 59, 75–86.
E. C. Lim, Proximity effect in molecular photophysics: dynamical consequences of pseudo Jahn-Teller interaction, J. Phys. Chem., 1986, 90, 6770–6777.
G. Bartocci, G. Galiazzo, G. Gennari, E. Marri, U. Mazzucato and A. Spalletti, Effect of the nature of aryl and heteroaryl groups on the excited state properties of asymmetric 1,4-diarylbutadienes, Chem. Phys., 2001, 272, 213–225.
J. Saltiel and Y.-P. Sun, Cis-trans isomerization of C?C double bond, in Photochromism: Molecules and Systems, eds. H. Dürr and H. Bouas-Laurent, Elsevier, Amsterdam, 1990, pp. 64–162 and references therein.
G. Favaro, F. Masetti, U. Mazzucato and P. Bortolus, Excited state reactivity of aza-aromatics. IV. Fluorescence properties and acid-base equilibria of naphthylpyridylethylenes, J. Phys. Chem., 1975, 79, 2785–2788.
A. Spalletti, U. Mazzucato, G. G. Aloisi and D. Pannacci, Excited state reactivity of aza-aromatics. X. Protonation effect on naphthyl- and phenanthryl-pyridyl-ethylenes, Z. Phys. Chem. Neue Folge, 1983, 138, 199–206.
J. P. Fouassier, D. J. Lougnot, I. Zuchowicz, P. N. Green, H. J. Timpe, K. P. Kronfeld and U. Müller, Photoinitiation mechanism of acrylamide polymerization in the presence of water-soluble benzophenones, J. Photochem., 1987, 36, 347–363.
A. R. Gregory, W. Siebrand and D. F. Williams, Electronic spectroscopy of trans-styrylpyridines and their conjugate acids, J. Am. Chem. Soc., 1979, 101, 1903–1904.
G. Orlandi, G. Poggi and G. Marconi, Lowest excited states of aza-analogues of stilbene. INDO/S calculation, J. Chem. Soc., Faraday Trans. 2, 1980, 76, 598–605.
Electronic Aspects of Organic Photochemistry, eds. J. Michl and V. Bonacký-Koutecky, Wiley Interscience, New York, 1990, pp. 98–100.
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This paper is dedicated to Professor Jean Kossanyi on the event of his 70th birthday.
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Mazzucato, U., Spalletti, A. Protonation effect on the excited state behaviour of EE-1-(n-pyridyl)-4-phenylbutadienes (n = 2, 3 and 4). Photochem Photobiol Sci 2, 282–288 (2003). https://doi.org/10.1039/b210695g
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DOI: https://doi.org/10.1039/b210695g