coo TPA

Chart 1

2 METHODS 2.1 Theoretical

The geometries of the isolated molecules were optimised using either the MM3-92 Allinger14 or MM+ molecular mechanics routines. The excited states were investigated by means of the Zerner Intermediate Neglect of Differential Overlap/Spectroscopic (ZINDO/S) method (Hyperchem software package). Electronic population analysis was performed by the Complete Neglect of Differential Overlap/Spectroscopic (CNDO/S) method with singly excited Configuration Interaction.

2.2 Experimental

Irradiations were performed with light at X > 310 nm. The incident light intensity was measured by using the ferrioxalate actinometer. Quantitative analysis of the degradation and decarboxylation yields was performed by High Performance Liquid Chromatography. All the details on the steady state experiments and on the analytical procedures can be found in refs.10 and 11.

Induced Circular Dichroism (i.c.d.) of racemic mixtures KPF, SPF and TPA in the presence of (3-cyclodextrin was performed by means of a Jasco J715 spectropolarimeter. The inclusion geometry of KPF was investigated by theoretically interpreting the i.c.d. signal. Conformational calculations based on a Dynamic Monte Carlo procedure including the solvent were used to find low energy associated structures.15"17 The rotational strength was calculated by using the Tinoco-Kirkwood approach.18 The most likely inclusion geometry was taken as that best reproducing the sign and the intensity of the i.c.d. bands. This procedure, detailed in ref. 13, proved to be very effective in interpreting the i.c.d. spectra of several chromophores included in cyclodextrins.19

Transient absorption spectra in the subnanosecond time domain were obtained by a pump-probe technique already described.20 Pump pulses of 35 ps (FWHM) at 266 nm were obtained from an actively-passively mode-locked Nd-YAG laser source (Continuum PY62-10). Time "zero" was assumed to be in the middle of the excitation pulse.

The setup for the nanosecond absorption measurements has been described previously.21 The excitation pulse, 20 ns FWHM, at 266 or 355 nm was from a Nd-YAG laser (JK-Lasers).

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