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Photoinduced Structural Volume Changes in Aqueous Solutions of Blepharismin
Author(s) -
Losi Aba,
Vecll Arnaldo,
Viappiani Cristiano
Publication year - 1999
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1999.tb03309.x
Subject(s) - aqueous solution , volume (thermodynamics) , chemistry , thermodynamics , physics
— Employing time‐resolved photoacoustics we measured the structural volume changes (ΔV ri ) occurring after photo‐excitation of blepharismin (BPR) aqueous solutions; an expansion occurring in the subnanosecond timescale is followed by a back contraction within some hundreds of nanoseconds. The magnitude of the ΔV ri strongly depends on pH, allowing the determination of the pK a of BPR with this method. The values so measured are very close to those found by means of UV‐visible absorption spectroscopy. The presence of water‐soluble electron acceptors or donors (hexacyanoferrate [III] hexacyanofer‐rate [II]) as well as the concentration of oxygen do not affect the magnitude or the kinetics of the structural volume changes. On the contrary, we detect a strong deuterium effect; this suggests that the observed ΔV ri are related to an altered hydrogen bond pattern of the excited state of the pigment with respect to the ground state. Comparative measurements with the parent compound hypericin are also reported, suggesting that the photo‐induced expansion‐contraction pattern is a general characteristic of polyhydroxylated quinones.