title: Calculation driven synthesis of an excellent dihydropyrene negative photochrome and its photochemical properties.
abstract: The photochromic properties of dihydropyrenes have been substantially improved by making use of density functional theory (DFT) activation barrier calculations, which suggested that the di-isobutenylcyclophanediene 15' should have a significant barrier to thermal isomerization to the dihydropyrene (DHP) 15, which itself should resist isomerization involving migration of the internal groups to the rearranged dihydropyrene 9 (X = -CH═C(Me)(2)). As a result of these calculations, the synthesis of the colorless cyclophanediene (CPD) 15' was undertaken and achieved from the dinitrile 28 in four steps in 37% overall yield %. The cyclophanediene 15' thermally isomerized to the dihydropyrene 15 at 100 °C with t(1/2) = 4.5 h, giving an extrapolated 20 °C t(1/2) of ∼16 y, consistent with the DFT calculations. No evidence for [1,5]-sigmatropic rearrangement in to 9 (X = -CH═C(Me)(2)) was observed on heating to 130 °C. The ring-opening isomerization quantum yields (ϕ(open)) for DHP 15 in to CPD 15' were determined in cyclohexane to be 0.12 ± 0.01, which is three times greater than for the benzoDHP 1. Friedel-Crafts naphthoylation of 15 gave 70% of purple 32, which in toluene showed the largest photochemical ring-opening isomerization quantum yields (ϕ(open)) of 0.66 ± 0.02 for any known dihydropyrene, ∼nine times greater than 1 in toluene. The thermal closing of 32' to 32, although faster than for 15', gave a useful extrapolated t(1/2) of ∼2 y at 20 °C.
authors.affiliation: Department of Chemistry, University of Victoria, P.O. Box 3065, Victoria, BC, Canada V8W 3V6.
authors.forename: Khurshid
authors.initials: K
authors.lastname: Ayub
authors.forename: Rui
authors.initials: R
authors.lastname: Li
authors.forename: Cornelia
authors.initials: C
authors.lastname: Bohne
authors.forename: Richard Vaughan
authors.initials: RV
authors.lastname: Williams
authors.forename: Reginald H
authors.initials: RH
authors.lastname: Mitchell