Double‐Layered 1,4‐Distyrylbenzene Chromophores–Synthesis, UV and Fluorescene Spectra

Abstract

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 Synthesis of Brominated Tetrafluoro[2.2]paracyclophanes

“…The bromination of cyclophane 1 is well investigated, [9,12] and varying the reaction conditions can result in monobromide as well as pseudo-para-and pseudo-meta-substituted products with very little para and pseudo-ortho-dibromides. Tri-and tetrabromides are all pseudo-para or pseudo-ortho isomers.…”

“…Selective conditions for the synthesis of monobromide 5 and dibromide 6 in high yields were observed -when pure bromine and a trace amount of iodine were used, i.e. König and de Meijere [12] conditions previously used for preparation of tetrabromide isomers of cyclophane 1.…”

“…For the cyclophane 1, however, the third and the fourth bromine, only accessible under harsh conditions, enter the same ring at the ortho and para positions to yield only two tetrabromide isomers. [12] Higher bromination of 6 yields two different tetrabromides 7 and 8. For the cyclophane 7, all bromides enter at the favorable meta position with respect to fluoromethylene groups.…”

“…General Bromination Procedure for 5, 6 and 11: [12] Tetrafluoro[2.2]-paracyclophane (1 or 2 mmol) was dissolved in 3-10 mL bromine and 1-2 small crystals of iodine were added. The loosely closed flask was wrapped in aluminium foil and left in the hood at room temp.…”

Suzuki aryl cross-coupling chemistry using derivatives of 1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane

“…1,2,2,9,9,10,paracyclophane (3) This compound was prepared from 1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane [1] by the published procedure [2]. 13 C NMR data for this compound have not been previously reported; 13 C{ 1 H} NMR d 141.90,133.72 (dd,J = 14.2,3.8 Hz),130.58,130.18,129.96,129.46,126.69 90 (dd,J = 170.6,6.7 Hz),133.72 (d,J = 170.6 Hz),130.58 (dd,J = 167.5,6.5 Hz),130.18 (dd,J = 166.9,6.7 Hz),129.96 (dd,J = 166.1,6.7 Hz),129.46 (dd,J = 168.4,6.7 Hz),126.69 (dd,J = 166.8,6.7 Hz) (aryl C-Hs); 94.85 (d, J = 9.3 Hz) (C-I); 136.67 (t, J = 7.3 Hz), 135.93 (d,J = 8.6 Hz),135.10 (t,J = 8.1 Hz),134.33 (t,J = 7.8 Hz) (cyclophane bridgeheads). 4.1.5.…”