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The cyclophane-type molecular dyads 1 x 2H and 1 x Zn, in which a doubly bridged porphyrin donor adopts a close, tangential orientation relative to the surface of a fullerene acceptor, were prepared by Bingel macrocylization. The porphyrin derivatives 2 x 2H and 2 x Zn with two appended, singly linked C60 moieties were also formed as side products. NMR investigations revealed that the latter compounds strongly prefer conformations with one of the carbon spheres nesting on the porphyrin surface, thereby taking a similar orientation to that of the fullerene moiety in the doubly bridged systems. Cyclic voltammetric measurements showed that the mutual electronic effects exerted by the fullerene on the porphyrin and vice versa are only small in all four dyads, despite the close proximity of the donor and acceptor components. The steady-state and time-resolved absorption and luminescence properties of 1 x Zn and 2 x Zn were investigated in toluene solution and it was shown that, upon light excitation, both the porphyrin- and the fullerene-centered excited states are deactivated to a lower-lying CT state, emitting in the IR spectral region (lambda max = 890 and 800 nm at 298 and 77 K, respectively). In the more polar solvent benzonitrile, this CT state is still detected but, owing to its very low energy (below 1.4 eV), is not luminescent and shorter-lived than in toluene. The remarkable observation of similar photophysical behavior of 1 x Zn and 2 x Zn suggests that a tight donor-acceptor distance cannot only be established in doubly bridged cyclophane-type structures but also in singly bridged dyads, by taking advantage of favourable fullerene-porphyrin ground-state interactions.

The photophysical and spectroscopic characterization of four new dimeric bis(BF 2 )-2,2 0 -bidipyrrins (BisBODIPYs) recently synthesized and characterized (Chem. Eur. J., 2008, 14, 2976-2983 has been undertaken along with that of the component BODIPY monomers. The monomers display the typical photophysical properties of this family; (i) narrow and intense single absorption band in the visible range at 530 nm; (ii) intense, solvent independent emission (F fl ca. 1); (iii) narrow emission band with a 200-400 cm À1 Stokes shifted emission, independent of solvent polarity; (iv) no absorption features for the singlet excited state; (v) very little triplet yield and no ability to sensitize singlet oxygen. The absorption spectra of the corresponding new dimers exhibit split band maxima in the visible range at about 490 and 560 nm, corresponding to an exciton splitting of ca. 2600 cm À1 . The luminescence in toluene is strong (F fl ca. 0.7, t =3.4 ns), broad and Stokes shifted by ca. 2200 cm À1 , but both luminescence yield and Stokes shift are solvent polarity dependent; F fl o 0.1, t o 1 ns and the Stokes shift is close to 2700 cm À1 in acetonitrile. Solvent viscosity does not appear to play an important role and freezing of the solvents to 77 K in a solid matrix cancels the differences in luminescence parameters. Singlet and triplet excited state absorbance was measured in toluene and acetonitrile and the ability of these new dyes to sensitize singlet oxygen was examined. The nature and dynamics of the excited state is discussed in comparison with the monomers properties and with some intra-or inter-molecular BODIPY dimers reported in the literature. Potential applications of these new dyes with respect to BODIPYs are pointed out on the basis of their spectroscopic and photophysical properties. Results and discussion Absorption in tolueneThe absorption spectra of some representative cases of the dimers studied in toluene solutions are reported in Fig. 1 with

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1,3-Dipolar cycloaddition of azomethine ylides to C60 leads to fulleroproline derivatives, in which a proline ring is fused on a 6,6-ring junction of the fullerene spheroid. This unnatural amino acid can be manipulated under standard coupling conditions to afford fulleroproline-containing peptides. All optically active fulleroproline derivatives and peptides display a characteristic maximum at 428 nm in CD spectra, which is diagnostic for the assignment of the absolute configuration of the Cα atom of the proline ring. Calculation of the CD spectra confirm the configurational assignment.

The effect of addition of the cyclodextrins (CDx) α-CDx and β-CDx on the photophysics and photochemistry of the dimethoxybenzenes (DMB) 1,4-DMB and 1,2-DMB in aqueous solution has been investigated by means of absorption, circular dichroism, fluorescence, and nanosecond transient absorption spectroscopies. The experimental results are discussed in the light of model calculations on the structure and the circular dichroism spectra of the DMB−CDx complexes. The association of 1,2-DMB with both CDxs is much weaker than that of 1,4-DMB owing to steric hindrance. With β-CDx, 1,4-DMB forms 1:1 complexes with a high association constant (K = 630 M-1) in spite of incomplete inclusion. Complexation of 1,4-DMB with α-CDx strongly affects the photophysical properties of the guest:  fluorescence is enhanced and triplet state decay slowed by a factor of 10 or more, depending on the decay reaction mode. Fluorescence enhancement is mainly due to a reduction of the rate constant for internal conversion. The effect of complexation on triplet decay was exploited for a detailed study of the association mechanism in terms of the consecutive formation of 1:1 and 1:2 complexes. Temperature-dependent measurements showed that both association steps are controlled by enthalpy−entropy compensation, the first step being entropy-driven and the second one enthalpy-driven. At lower temperatures (T < 50 °C), 1:2 complex formation predominates. These findings are supported by the circular dichroism spectra and the model calculations. There is no significant effect of complexation with either α- or β-CDx on hydrated electron ejection from 1,4-DMB, but the eaq - decay is accelerated in the presence of β-CDx. This is tentatively attributed to spatial correlation between eaq - and radical cations induced by complexation.

The photodecarboxylation reaction of 2-(3-benzoylphenyl)propionate (ketoprofen anion, KP-) was studied in water and in 0.1 M phosphate buffer solutions in the pH range 5.7-11.0 by laser-induced optoacoustic spectroscopy (LIOAS, T range 9.5-31.6 degrees C). Upon exciting KP- with 355 nm laser pulses under anaerobic conditions, two components in the LIOAS signals with well-separated lifetimes were found (tau 1 < 20 ns; 250 < tau 2 < 500 ns) in the whole pH range, whereas a long-lived third component (4 < tau 3 < 10 microseconds) was only detected at pH < or = 6.1. The heat and structural volume changes accompanying the first step did not depend on pH or on the presence of buffer. The carbanion resulting from prompt decarboxylation within the nanosecond pulse (< 10 ns) drastically reduces its molar volume ([-18.9 +/- 2.0] cm3/mol) with respect to KP- and its enthalpy content is (256 +/- 10) kJ/mol. At acid pH (ca 6), a species is formed with a lifetime in the hundreds of ns. The enthalpy and structural volume change for this species with respect to KP- are (181 +/- 15) kJ/mol and (+0.6 +/- 2.0) cm3/mol, respectively. This species is most likely a neutral biradical formed by protonation of the decarboxylated carbanion, and decays to the final product 3-ethylbenzophenone in several microsecond. At basic pH (ca 11), direct formation of 3-ethylbenzophenone occurs in hundreds of ns involving a reaction with the solvent. The global decarboxylation reaction is endothermic ([45 +/- 15] kJ/mol) and shows an expansion of (+14.5 +/- 0.5) cm3/mol with respect to KP-. At low pH, the presence of buffer strongly affects the magnitude of the structural volume changes associated with intermolecular proton-transfer processes of the long-lived species due to reactions of the buffer anion with the decarboxylated ketoprofen anion.

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