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

Abstract

The novel 2,7-bis((TIPS)ethynyl)-10b,10c-diethyldihydropyrene photochrome (TIPS = triisopropylsilyl) was observed to undergo thermal rearrangement to 2,7-bis(TIPSethynyl)-pyrene in the solid state. The transformation proceeds stepwise with ethyl groups "dancing" out of the dihydropyrene core toward the periphery of the polycyclic framework. The formation of two regioisomers occurs initially and is followed by two progressive de-ethylations to give a pyrene. This transformation occurs in the solid crystalline state and represents a unique example of a single-crystal-to-single-crystal (SC-SC) transformation involving C−C bond cleavages with hydrocarbon fragments escaping the ordered crystalline structure. Detailed characterizations of the transformation by in situ temperaturedependent X-ray single-crystal diffraction supported by thermal analysis, HPLC-mass spectrometry experiments, NMR spectroscopy, and theoretical calculations, are reported.

2,7- and 4,9-Dialkynyldihydropyrene Molecular Switches: Syntheses, Properties, and Charge Transport in Single-Molecule Junctions

“…The structures of 21a and 22b are depicted in Scheme . We have reported the X-ray structure of 22b , and its unusual thermal single-crystal-to-single-crystal transformation elsewhere …”

“…thermal single-crystal-to-single-crystal transformation elsewhere 67. Syntheses of Target Molecules for Conductance Studies.…”

Photo‐Responsive Hydrogen‐Bonded Molecular Networks Capable of Retaining Crystalline Periodicity after Isomerization

“…1 H NMR spectrum of the decomposed compounds indicates that the thermal decomposition was proceeded by 1,5-sigmatropic shift of the inner methyl groups and irreversible cascade reactions (Figure S22), which was reported on DHP derivatives. [54] These indicate thermal limitation of the present systems.…”

Functionalised organometallic photoswitches containing dihydropyrene units

“…11 A multi-layer assembly of thin-film DHP containing polymers has also demonstrated conductance switching induced by irradiation. 12 Most recently, we have explored the unique thermally activated single-crystal-tosingle-crystal alkyl shift across the DHP core, 13 and measured the conductance of 4,9 and less common 2,7 ethynyl-substituted DHPs with pyridyl contact groups. 14 Metal σ-alkynyl complexes are attractive platforms for molecular electronics given their tunability and accessibility.…”