Unveiling how intramolecular stacking modes of covalently linked dimers dictate photoswitching properties

Abstract

Covalently linked π-stacked dimers represent the most significant platform for elucidating the relationship between molecular alignments and their properties. Here, we present the one-pot synthesis of two intramolecularly π-stacked dimers and disclose how intramolecular stacking modes dictate photoswitching properties. The dimer, which features cofacially stacked chromophores and geometrically favours intramolecular photochemical [2 + 2] cycloadditions, displays a nearly irreversible photoswitching behaviour. By contrast, the dimer, bearing crosswise stacked chromophores, is geometrically unfavourable for the cycloaddition and exhibits a highly reversible photoswitching process, in which the homolysis and reformation of carbon−carbon single bonds are involved. Moreover, the chiral carbon centres of both dimers endow these photoswitches with chirality and the separated enantiomers exhibit tuneable chiroptical properties by photoswitching. This work reveals that intramolecular stacking modes significantly influence the photochemical properties of π-stacked dimers and offers a design strategy toward chiral photoswitchable materials.

Flexible and Continuous Regulation Promoting Remarkably Emission Enhancement of Planar Triphenylene

“…Organic luminescent materials with π-conjugated structures have attracted much attention, because of their academic importance and promising applications in optical storage, optoelectronic devices, and display devices. − Under most circumstances, organic luminophores are applied in various fields in the form of aggregates, and the molecular packing mode of aggregates is particularly important to their functions. , Actually, many factors including inherent electronic properties, intermolecular interactions, overlap degree, and distances between adjacent π-conjugated molecules will determine the molecular packing status in the solid state and then affect their luminescence properties. , In order to regulate the arrangement of aggregated molecules, one way is to control different degree of π–π interactions between π-conjugated moieties by polymorph-dependent solid-state structure. − Moreover, the modification of molecular structure is also a common approach to control stacked π-systems (such as the introduction of bulky unit and polar group) and obtain luminescent materials with desired photophysical properties. − Also, various scaffolds have been widely used in order to regulate the distance between π-conjugated units accurately (Figure A), including, for instance, xanthene, [2,2]­paracyclophane, calix[4]­arene, and m -terphenyl oxacyclophane, which have been used to fix the π-planes and completely adjust molecular packing qualitatively or quantitatively to tune luminescence properties of π-conjugated materials in aggregates. , However, this type of experiment can only be performed in relatively few samples with limited information on the relationship between the emissive properties and the distances of two π-planes, because of the complicated synthetic demands involved and uncontrollable molecular packing. Actually, so far, there are few reports focused on the revealing of the continuous change of the luminescence upon the continuous modulation of the distance between planar π-systems, although it is badly required to establish the relationship of molecular packing-luminescence property.…”

“…12−14 Also, various scaffolds have been widely used in order to regulate the distance between πconjugated units accurately (Figure 1A), including, for instance, xanthene, [2,2]paracyclophane, calix [4]arene, and m-terphenyl oxacyclophane, which have been used to fix the π-planes and completely adjust molecular packing qualitatively or quantitatively to tune luminescence properties of π-conjugated materials in aggregates. 15,16 However, this type of experiment can only be performed in relatively few samples with limited information on the relationship between the emissive properties and the distances of two π-planes, because of the complicated synthetic demands involved and uncontrollable molecular packing. Actually, so far, there are few reports focused on the revealing of the continuous change of the luminescence upon the continuous modulation of the distance between planar π-systems, although it is badly required to establish the relationship of molecular packing-luminescence property.…”