The syntheses and photochromic properties of several substituted and condensed benzo[e]dimethyl-dihydropyrenes

Date

2017-05-01

Authors

Wang, Yunxia

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Abstract

The symmetric multistate photo-switchable molecule 72, which contains two DHP units with a dibenzocyclophane as a spacer, was successfully synthesized by different routes using aryne-furan type Diels-Alder reactions. In the course of making 72, the intermediate furan 79 was synthesized, which upon deoxygenation gave photo-switchable furan 82. In a study of substitution effects on benzo[e]pyrene 21, the substituents phenyl, acetyl, nitro and phenylethynyl were attached to the 4,5-positions. The acetyl and nitro groups were introduced by direct substitution of 21, while coupling methodology were used for the phenyl and phenylethynyl groups. In the later case, a Suzuki coupling was used on bromide 69, followed by bromination, or a Sonogashira coupling was used on the bromoiodide 100, and then an aryne-furan Diels-Alder reaction and deoxygenation were used to give the final substituted benzo[e]pyrenes 105 and 103. The successful synthesis of the phenylbenzo[e]pyrene 105 enabled us to access the monosubstituted tris-pyrene system 120 through the reaction of bromophenylpyrene 107 and furan 79. The thermal return reactions (cyclophanediene to dihydropyrene) were studied on the benzo[e]pyrene derivatives and multistate photoswitch systems. Although the activation energies and enthalpies do not change much with substitution, the thermal return rates do appear to decrease with an electron withdrawing substituent. Photochromic studies were performed on 72 and 120. They both opened in a stepwise manner with one DHP ring opening and then the other, though the intermediate could not be isolated. A simple comparison of the photo opening and closing rates relative to benzo[e] pyrene 21 was performed under excess light conditions. All the derivatives of 21 synthesized in this thesis had faster visible opening rates than the parent 21; the UV closing rates did not change much however.

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Photochemistry

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