Effect of Transannular π−π Interaction on Emission Spectral Shift and Fluorescence Quenching in Dithia[3.3]paracyclophane−Fluorene Copolymers

Abstract

A series of dithia[3.3]paracyclophane−fluorene copolymers 1a − c and 3 − 5 were synthesized by a palladium-catalyzed reaction between 9,9-di-n-hexylfluorene-2,7-bis(trimethylene boronate) and the corresponding dithiacyclophane precursors. The transannular π−π interaction in the dithiaparacyclophane modified the electronic and optical properties of the copolymers significantly, resulting in emission red shifts relative to a reference polymer 2. The observed shift in 1a and 5 was accompanied by enhanced photoluminescence (PL) efficiency, whereas that in 1b, 1c, 3, and 4 experienced a significant to nearly complete fluorescence quenching. The quenching effect is likely to involve an electron-transfer process and could be correlated qualitatively to the reduction potential of the “external” aromatic moiety in the cyclophane unit.

Violet‐to‐Blue Tunable Emission of Aryl‐Substituted Dispirofluorene–Indenofluorene Isomers by Conformationally‐Controllable Intramolecular Excimer Formation

“…It is hence reasonable to assume that the shielding of the hydrogen atoms borne by the fluorene units, in 2 a , results from their face‐to‐face geometry and not from their different indenofluorenyl central core. Indeed, transannular π–π interactions are usually accompanied by high field shifts in 1 H NMR spectra9, 32–35 and have been observed in different systems such as for example acridylnaphthalene,32 paracyclophane,35 polyfluorene,9, 34 thiophene derivatives15 and tetrapyrenyl compounds 36. The t Bu‐substituted derivatives 1 b and 2 b rigorously present the same behavior as that reported above for 1 a and 2 a (Table S2).…”

Blue Emitting 3 π–2 Spiro Terfluorene–Indenofluorene Isomers: A Structure–Properties Relationship Study

“…This shielding effect observed in (2,1-a)-DST-IF has been assigned to intramolecular p-p interactions between face-to-face terfluorenyl moieties. Indeed, transannular p-p interactions are usually accompanied by high-field shifts in 1 H NMR spectra and have been observed in different systems such as acridylnaphthalene, [37] paracyclophane, [38] polyfluorene, [39,40] or ethynyltriphenylene [41] or thiophene derivatives. [42] Thus, p-p interactions occur between the two cofacial terfluorenyl moieties of (2,1-a)-DST-IF and should lead to significantly different electrochemical and optical properties compared to its isomer (1,2-b)-DST-IF, as discussed next.…”

Modulating the Physical and Electronic Properties over Positional Isomerism: The Dispirofluorene–Dihydroindacenodithiophene (DSF‐IDT) Family

“…Indeed, trans-annular π-π interactions are usually accompanied by high field shifts in 1 H NMR spectra. [48][49][59][60][61][62][63] In [2,1-b]-DSF-IF, H10 is also found at a high field, 6.11 ppm, [39] but remains nevertheless less shielded than in meta-DSF-IDT. Thus in meta-DSF-IDT, the presence of (i) thienyl rings and (ii) cofacial fluorenes both contribute to the strong shielding of the central proton H10 below 6 ppm.…”