The syntheses and properties of photochromic systems based on dimethyldihydropyrenes




Bandyopadhyay, Subhajit.

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This thesis explores substituent effects on the photochromism of the benzo[e]dimethyldihyropyrene system 3. Thus systems with conjugated connectors, (25, 29, 33, 34), a system with conjugation and then insulating connector (31), one with an organometallic connector (32), and a system functionalized on the benzene ring (35), were synthesized and their photochemical studies were carried out. Comparisons of the photo opening and closing rates relative to benzo[e]pyrene 3 under similar conditions were performed. All the derivatives of 3 synthesized (except for the ferrocenyl product 32) had faster visible opening rates than the parent 3; the UV closing rates for most of the derivatives were are almost the same as that of the parent 3. Several linked photochromes having two photochromic units have been successfully synthesized from their monomeric precursors using metal mediated coupling reactions. Both photochromic units of the bis-switches, 41 and 54 open and close, although it is not possible to address each photochrome independently. UV closing of the open-open forms of the bis-photochromes occur via the open-closed intermediate. Thus 41 and 54 act as multiple state switches. In the case of 49 only one photochromic unit of the bisphotochrome opened. However, none of the photochromic units in 38 opened. The thermal return reactions (cyclophanediene to dihydropyrene) were studied on the benzo[e]dihydropyrene derivatives and linked bis-photochromic systems and the energy of activation of the thermal reversal and the half-lives were determined to be similar or 1- 2 kcallmol less than the benzo system 3.