In moderately acidic water/ethanol solutions, 7-(naphthalen-2-ylmethyl)-5,6-dihydrobenzo[c]xanthen12-ium perchlorate shows C-H proton acidity giving rise to an ethylenic base species, instead of the hydration products of the typical flavylium network of chemical reactions, hemiketal, cis-chalcone and trans-chalcone. The kinetics of this acid-base process is much slower, k(obs)(s(-1)) = 3.5 x 10(-3) + 0.16[H(+)], than those commonly observed for O-H deprotonation. In the presence of the triblock copolymer Pluronic F-127, the ethylenic base is dramatically stabilized shifting the pK(a) from 1.35 (in ethanol : water (1 : 1) to -0.35. Taking profit from the well-described temperature dependence of this polymer, a phase transition thermochromic system was achieved. The system was cycled between 5 and 35 degrees C with negligible changes in absorbance after 20 cycles.
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Cited Reference Count: 60
Avo, Joao Jorge Parola, A. Lima, Joao C. Pina, Fernando Cunha-Silva, Luis
Pina, Fernando/C-8161-2011; Cunha-Silva, Luis/A-8765-2012; Parola, A. Jorge/F-4048-2010; Avo, Joao/C-6939-2013; Caparica, PTNMR/E-5112-2013; Caparica, cqfb_staff/H-2611-2013; REQUIMTE, AL/H-9106-2013; Chaves, Pedro/K-1288-2013; Lima, Joao/F-3658-2010
Parola, A. Jorge/0000-0002-1333-9076; Lima, Joao/0000-0003-0528-1967
Fundacao para a Ciencia e Tecnologia [PTDC/QUI-QUI/104129/2008, PTDC/QUI/67786/2006]; programme "Ciencia"; [SFRH/BD/65127/2009]
This work was supported by Fundacao para a Ciencia e Tecnologia through projects PTDC/QUI-QUI/104129/2008 and PTDC/QUI/67786/2006, programme "Ciencia 2008" (LCS) and PhD grant SFRH/BD/65127/2009 (JA).
Royal soc chemistry
Cambridge