The dipole moments of four photochromic derivatives of indolinospirobenzopyran have been studied in their spiro and their open merocyanine form, in dioxane. Determinations have been done by electrooptical absorption measurements (EOAM). To prepare either a pure spiropyran or a pure merocyanine form solution, the experimental setup had to be modified by addition of a second light beam. In this way thermal equilibration between the spiropyran and the merocyanine form and switching from one form to the other induced by the measuring light beam could be avoided. The ground-state dipole moment of the spiro form amounts to (10-15) × 10 -30 C m and increases strongly to about 60 × 10 -30 C m with the excitation to the first excited singlet state. The ground-state dipole moment of the merocyanine form is much larger and amounts to (50-60) × 10 -30 C m. In contrast to the spiro form it decreases to about 40 × 10 -30 C m, when exciting to the first excited singlet state of the merocyanine form. † Part of the special issue "Noboru Mataga Festschrift".

We report the first ultrafast ring closure kinetics of the merocyanine (MC) of a reverse photochromic spiropyran 1′,3′,3′-trimethyl-6,8-dinitrospiro[2H-1-benzopyran-2,2-indoline] (6,8-dinitro BIPS) and its 1′-(2-carboxyethyl) substituted derivative. The reaction is fast and essentially over in a few hundred picoseconds. The rate of MC-S 1 state decay evaluated from transient absorbance can be correlated directly with the MC-S 1 state lifetime as determined using stimulated and ordinary emission measurements. The recovery of the MC-S 0 state from MC-S 1 has a component with a lifetime of 60-78 ps in acetonitrile with a second component of 350-470 ps probably due to a metastable intermediate. We can further establish that the excited MC-S 1 state takes on the order of 500 fs to form from higher-energy states after photoexcitation with 390 nm light. † Part of the special issue "Noboru Mataga Festschrift".

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