Interchromophore orientation scaffolding by m-terphenyl oxacyclophanes

Abstract

Modular oxacyclophanes featuring m-terphenyl units scaffold inter-pi-system interaction in face-to-face stacked or orthogonal orientations, leading to distinct photophysical properties.

Covalently Scaffolded Inter‐π‐System Orientations in π‐Conjugated Polymers and Small Molecule Models

“…The mterphenyl oxacyclophane that served as a canopy unit in 9, e.g., has been used to scaffold interactions between two PPE model chromophores in two different geometries ( Figure 11). [46] Structure 11a features the chromophores oriented with planes parallel and long axes tilted with respect to one another at an angle (b ¼ 218) and a centroidcentroid distance (3.86 Å ) between the central ring of each p-system. In contrast, the planes of the two chromophore segments in 11d are nearly orthogonal (a ¼ 898), the long axes are substantially tilted (b ¼ 698), and the centroid-centroid distance is 5.39 Å (somewhat longer than typical for edgeface interactions).…”

Conjugated Polymers Featuring Oxacyclophane‐Scaffolded π‐Stacking Interactions

“…Our group has developed synthetic routes to halogen‐derivatized oxacyclophanes and established methodologies for functionalizing them with chromophores via the Sonogashira reaction to yield compounds such as M5 and M6 (Figure ) . The synthetic route to precursor 3 , which is needed to prepare the focal compounds for this study, oxacyclophane‐bridged conjugated polymer CyP and model CyM is shown in Scheme A.…”

“…[24][25][26][27] Other researchers have devised molecular scaffolding and covalent crosslinking strategies to constrain adjacent polymer chains in near-ideal orientations to improving charge/ energy transport through a material. [ 23,28 ] Two of the scaffolding most relevant to the current work are the [2.2] paracyclophane [29][30][31] (i.e., in P3 , Figure 1B) and the oxacyclophane [ 26,32 ] (i.e., in M5 , M6 , CyM , and CyP , Figure 1 ) scaffolding units. The [2.2]paracyclophane unit enforces a rigid face-to-face π-stacking interaction between its two phenyl rings at a separation of 2.98 Å, a distance smaller than what can be achieved with polymer chains that are not covalently scaffolded.…”

Conjugated polymers with regularly spacedm-phenylene units and post-polymerization modification to yield stimuli-responsive materials

“…This has been done with success for a wide range of organic polymers, including CPs such as hyperbranched poly( p ‐phenylene ethynylene)s and some poly( p ‐phenylene vinylene)s in which the conjugation is periodically disrupted by m ‐phenylene units. Derivatives of P1‐I (Chart ) in which the iodo substituent is replaced by small‐molecule chromophores have shown low incidence of interchain interactions while enforcing intrachain interactions between the backbone π ‐system and the small‐molecule chromophore, leading to intramolecular charge transfer and Forster resonance energy transfer (FRET) …”

“…Both small molecules (Chart (A)) and polymers (Chart (B)–(D)) have proven useful for fluorescence‐based detection of nitroaromatics . In each of these cases the bulky side chains such as iptycenes (Chart (A) and (B)), cyclophane‐containing ‘canopy’ (Chart (C)) and m ‐terphenyls (Chart (D)) provide free volume around a π ‐conjugated fluorophore for analyte occupancy. Crosslinked conjugated microporous polymer networks likewise provide the free volumes necessary for efficient nitroaromatic entry and detection …”