Two 1,1-diphenylethenes bearing either a 4-dimethylamino or 4-methoxy group as electron donor and a 4Ј-cyano group as electron acceptor, as well as compounds containing only a donor or acceptor functionality, were synthesized. The observation of strong fluorescence solvatochromism (originating from a biradicaloid twisted intramolecular charge-transfer state) of the donor-acceptor compounds reveals that photoinduced charge separation through the cross-conjugated 1,1-diphenylethene spacer occurs. The presence of weak charge-transfer absorption bands in the UV spectra re-

The bacterial mutagenic response (Ames-assay, Salmonella typhimurium strain TA98 ± S9-mix) of a series of monocyclopentafused polycyclic aromatic hydrocarbons (CP-PAHs) identified in combustion exhausts, viz. cyclopenta[cd]pyrene (1), acephenanthrylene (2), aceanthrylene (3) and cyclopenta[hi]chrysene (4), is re-evaluated. The mutagenic effects are compared with those exerted by the corresponding partially hydrogenated derivatives, 3,4-dihydrocyclopenta[cd]pyrene (5), 4,5-dihydroacephenanthrylene (6), 1,2-dihydroaceanthrylene (7) and 4,5-dihydrocyclopenta[hi]chrysene (8). It is shown that the olefinic bond of the externally fused five-membered ring of 1, 3 and 4 is of importance for a positive mutagenic response. In contrast, whilst CP-PAH 2 is found inactive, its dihydro analogue (6) shows a weak metabolism-dependent response. The importance of epoxide formation at the external olefinic bond in the five-membered ring is substantiated by the bacterial mutagenic response of independently synthesized cyclopenta[cd]pyrene-3,4-epoxide (9), acephenanthrylene-4,5-epoxide (10), aceanthrylene-1,2-epoxide (11) and cyclopenta[hi]chrysene-4,5-epoxide (12). Their role as ultimate, active mutagenic forms, when CP-PAHs 1, 3 and 4 exhibit a positive mutagenic response, is confirmed. Semi-empirical Austin Model 1 (AM1) calculations on the formation of the CP-arene oxides (9-12) and their conversion into the monohydroxy-carbocations (9a-12a and 9b-12b) via epoxide-ring opening support our results. For 2 and 4, which also possess a bay-region besides an annelated cyclopenta moiety, the calculations rationalize that epoxidation at the olefinic bond of the cyclopenta moiety is favoured.

Functionalized basket-shaped hosts have been synthesized from the concave building block l,3:4,6-bis(3,6-dihydroxy-l,2-xylylene)tetrahydro-3a,6a-diphenylim idazo [4,5-d]im idazole-2,5(l//,3H )-dione (1). T o this end, N -substituted l,4,10,13-tetraoxa-7-azatridecam ethylene bridges were attached to the 3,6-and 3',6'-positions of the xylylene rings of 1. T h e substituents at the nitrogen atom in the bridge include: 5-hydroxy-3-oxapentyl, benzyl, hydrogen, 5-(N-(benzyloxycarbonyl)-L-histidyl)-3-dioxapentyl, and 5-acetyl-3-oxapentyl. T h e baskets complex alkali m etal and am m onium guests, as well as aliphatic and arom atic diam m onium guests, all in a 1:1 ratio. Using the picrate extraction technique, free energies of binding for the new hosts with 19 guests were determined. Extremely strong binding (-AG° values up to 18 kcal mol-1) was observed for the complexes between the hosts and o-phenylenediam m onium dipicrate. T he origin of this phenom enon is discussed. T he host with histidyl substituents easily forms a 1:1 complex with Zn(O Tf)2.

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Intramolecular excimer emission is observed for cis-1,4-di(1-pyrenyl)decamethylcyclohexasilane in nonpolar solvents. Time-resolved fluorescence spectroscopy and kinetic modelling indicate that the driving force of excimer formation is very small, and that the process is governed by the flexibility of the silicon ring. In the polar solvent acetonitrile, photoinduced electron transfer occurs, with the cyclohexasilane ring acting as electron donor and the pyrenyl group as electron acceptor. Ó