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.

Reactivity of a pyridinium-substituted dimethyldihydropyrene switch under aerobic conditions: self-sensitized photo-oxygenation and thermal release of singlet oxygen

“…Importantly, the properties of this molecule can be finely tuned by chemical functionalization, a feature that has enabled the recent development of very promising DHP-based multi-functional materials and opto-electronic devices. 10,[37][38][39][40][41][42][43][44] We have recently investigated the behavior of 1 (closed isomer as PF 6 salt, Scheme 1) under an inert atmosphere. 45 The presence of the pyridinium substituents on the DHP core has been shown to significantly improve the photoisomerization efficiency in terms of photoconversion rate and to allow a significant decrease of the irradiation energy (from green to red light).…”

“…Importantly, the properties of this molecule can be finely tuned by chemical functionalization, a feature that has enabled the recent development of very promising DHP-based multi-functional materials and optoelectronic devices. 10,[37][38][39][40][41][42][43][44] We have recently investigated the behavior of 1 (closed isomer as PF 6…”

Improving Fatigue Resistance of Dihydropyrene by Encapsulation within a Coordination Cage

“… 4 Unlike other photochromic systems, such as azobenzenes and spiropyrans, DHP is a rare example of a compound where the colored form constitutes the thermodynamically more stable isomer. 5 One disadvantage of this molecular switch, however, is its instability and poor fatigue resistance. The observed fatigue is thought to arise from the reactivity of the biradical intermediate formed as a result of photocleavage of the central C–C bond in the singlet excited state of DHP.…”

Light gated reversible modulation of Cu2+ binding

“…The fractions of the closed forms at different irradiation intervals under identical conditions roughly correlate with the relative quantum efficiencies of the ring opening/closing reaction. 10,13 Dihydropyrenes are negative photochromes and hence show thermal (2)…”