Oligothiophene Functionalized Dimethyldihydropyrenes I: Syntheses and Photochromicity

Abstract

The syntheses of 2,7-di-tert-butyldimethyldihydrobenzo[e]pyrenes with thienyl (6), terthienyl (7), and pentathienyl (14) side chains at the 4,5- positions, ter- and pentathienyl side chains at the 4-position with ter- (39) and pentathienylcarbonyl (40) side chains at the 10- and 11-positions, 2-naphthoyl-7-tert-butyldimethyldihydropyrenes with ter- (53), penta- (54), and septithienyl (55) side chains at the 4,9-positions are described. These compounds are all photochromic and open to the corresponding cyclophanedienes with long wavelength (>490 nm) light, and as such, the conjugative path could change considerably, making them suitable to investigate as potentially switchable conducting molecules. In this paper, the syntheses and the photochemical and thermal isomerizations are studied; in the accompanying paper, the electrochemical and conductive properties are studied. Here, a comparison of the relative opening rates to that of the benzo[e]pyrene 4 (with no thienyl substituents) is made, and all of the above photochromes show considerably enhanced photo-opening of the DHPs to the CPDs. As examples, 14, 40, and 54 were cycled between the open and closed forms, and no decomposition was observed; however, when 54 was irradiated for 40 h with 254 nm light, some radicals did form, which enhanced the thermal closing rate, and so extensive irradiation with short wave UV is better avoided. The thermal closing reactions were also studied, and all of the above compounds close faster than benzo-CPD 4', though for the highly photochromic ter- and pentathienyl benzo-CPDs 39' and 40', the rate was not too enhanced from that of 4' and so are probably the best compromise between fast photochromicity and slow thermal reversion.

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…”

A Merry Dance Across the π-Cloud: Tracking the Transformation of a 2,7-Substituted Dihydropyrene Through a Thermally Stimulated Single-Crystal-to-Single-Crystal Reaction

“…DHPs are of great interest in functional materials and molecular electronics due to their high tunability, lack of photostationary states, minimal structural reorganization between isomers, and the stability of the closed, more conductive, isomer. , Certain DHPs undergo a thermal rearrangement of internal substituents at elevated temperatures that is initiated by a 1,5-sigmatropic shift of the substituents and irreversibly cascades toward the expulsion of these groups to form, in very limited examples, pyrene. , Such decomposition was first characterized when heating 1b (R = Et, Scheme ), but the structure of the thermal isomer remained obscure . DHP 1a (R = Me) undergoes a transformation to 3a (R = Me) above 200 °C that results in a loss of the intense green color and shifts in the visible absorption spectrum, while DHP 1b and its propyl analogue 1c undergo thermal rearrangement at 81 °C .…”

Chirality and Circular Polarized Properties of Photochromic Polyaromatic Molecules

“…However, their low photochromic efficiency remains as a barrier to further applications. It has been reported that benzene-[e]-annelated DHP shows greatly improved switching rates [20,30].…”

“…In these compounds, dihydropyrenes (DHPs) are negative photochromic polyaromatics [8] that undergo wavelength-dependent reversible photoisomerization between dark green closed and colorless open forms (Figure 2) [9][10][11][12][13].…”