The production of triplet states in basic solution of
tetrakis(tetrasulfonated-phenyl)porphyrin (TPPS4)
is
accompanied by a contraction of (10 ± 3) mL/mol as determined by
laser-induced optoacoustic spectroscopy
(LIOAS) at different temperatures. The contraction is reverted as
the triplet decays. The volume changes
should mainly originate in changes in the solvation sphere due to the
entire process of ground state to triplet
transition (for the contraction) and back to the ground state (for the
expansion). The presence of oxygen has
no major effect on the contraction and the expansion observed. The
present study shows that TPPS4 is not
suitable as a calorimetric reference, contrary to our own hypothesis in
Heihoff et al.
Photochem. Photobiol.
1990, 51, 635−641. It was also observed
that triplet state formation of methylene blue and rose bengal
is
accompanied by a structural volume change of −1.5 and 1 mL/mol,
respectively.