The reaction of [2.2]paracyclophane (1) with liquid bromine The molecular structure of ?a has been established by X-ray affords a 1: 1 mixture of only two isomeric products, the structure analysis. The UV and fluorescence spectra of a vapseudo-para 2 and pseudo-orfho tetrabromide 3. The structure riety of substituted products are reported and compared with of the pseudo-para isomer 2 has been determined by X-ray those of the parent chromophors 2,5-dimethyl-l,I-distyrylbenstructure analysis. Fourfold palladium-catalyzed coupling zene (16) and 2,5-diethyl-1,4-bis(phenylethynyl)benzene (17), with styrenes and with methyl acrylate converts 2 and 3 into respectively. double-layered derivatives as e.g. 6a, ?a, and 7b, respectively.The UV and fluorescence spectra of aromatic systems change remarkably with the extent of conjugation. But besides these intramolecular effects intermolecular interactions lead to phenomena such as fluorescence of excimers ['I or intense charge-transfer absorptions. The response of a composite chromophor to light is strongly influenced by the relative orientation of its subunits. Chemical bonds between chromophoric subunits can generate composite chromophors of fixed geometry with enhanced charge-transfer interaction. This has been verified inter alios by Staab et all2] using the [2.2]paracyclophane skeleton to hold two chromophoric units at close distance with a rigid geometry. In view of the strong R,Rinteraction between the aromatic rings in [2.2]para~yclophane[~], one can think of an electronic coupling between two chromophors "clamped" together at such a distance. As 1,4-di~tyrylbenzene[~~ is a well established commercially available laser dye, we have set out to test the spectroscopic properties of [2.2]paracyclophane derivatives containing two 1,4-distyrylbenzene units and similar "double-layered" chromophores.

The determination of physically meaningful thermal ellipsoids for hydrogen from X‐ray diffraction data was achieved in the X‐ray structure analysis of N, N′‐dimethylindigo (1) by synchrotron radiation. Owing to the steric interactions of the CH3 groups with the carbonyl O atoms, the molecule is slightly twisted. This explains the bathochromic absorption of 1 in comparison to that of indigo and was also predicted from calculations.

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The reaction of 2 with nBuLi at -78°C generates aryne intermediates within the aromatic rings of [2.2]paracyclophane which are trapped in Diels-Alder reactions with dienes like furan, 1,9-diphenylisobenzofuran, or cyclopentadiene. Reductive deoxygenation with low-valent titanium reagents or oms cannot be removed anymore by reduction. TMSI converts the adducts of furan and isobenzofuran into

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