PHOTOPHYSICAL CHARACTERIZATION OF A PHOTOCHROMIC SYSTEM. THE CASE OF MEROCYANINE 540

P. F. ARAMENDIA; R. DUCHOWICZ; L. SCAFFARDI ; J. O. TOCHO

JOURNAL OF PHYSICAL CHEMISTRY A

AMER CHEMICAL SOC

Lugar: Washington; Año: 1990 vol. 94 p. 1389 - 1392

1089-5639

The fluorescence emission of merocyanine 540 (MC540) in 95% ethanol was studied under continuous irradiation. Fluorescence spectra from excited states of both normal (N) and photoisomeric (P) species are identical. The laser fluence dependence of the fluorescence intensity is interpreted on the basis of a photochromic system involving N and P ground states and firstexcited singlet states. Common flash photolysis equations are generalized in order to include a photoequilibrium between isomers. The emission data are used together with previous flash photolysis and optoacoustic results to obtain P fluorescence and photoisomerization quantum yields as 0.07 * 0.02 and 0.20 A 0.04, respectively, P absorption cross section at the maximum(560 nm) as 4.74 X cm2 (125 X IO3 M-l-cm-l), and the energy difference between the ground states as 165 kJ.mol-I. Internal conversion, which can take place as a direct process or through a twisted state, is the main deactivation pathway for excited singlet P.