Molecular Actuator: Redox-Controlled Clam-Like Motion in a Bichromophoric Electron Donor

Métivier

et al. 2011

114

Two series of DiSpiroFluorene-IndenoFluorene (DSF-IF) positional isomers, namely dispiro[2,7-diarylfluorene-9',6,9'',12-indeno[1,2-b]fluorenes], (1,2-b)-DSF-IFs 1 and dispiro[2,7-diarylfluorene-9',6,9'',12-indeno[2,1-a]fluorenes], (2,1-a)-DSF-IFs 2 have been synthesized. These violet-to-blue fluorescent emitters possess a 3π-2spiro architecture, which combines via two spiro links two different indenofluorene cores, that is, (1,2-b)-IF or (2,1-a)-IF and 2,7-substituted-diaryl-fluorene units. Due to their different geometric profiles, the two families of positional isomers present drastically different properties. The marked difference observed between the properties of (1,2-b)-DSF-IF (1) and (2,1-a)-DSF-IF (2) is discussed in terms of intramolecular π-π interactions occurring in (2,1-a)-DSF-IF (2) leading to conformationally-controllable intramolecular excimer formation. Indeed, the original geometry of the (2,1-a)-DSF-IF (2) family, with face-to-face "aryl-fluorene-aryl" moieties, leads to remarkable excimer emission through intramolecular π-π interactions in the excited state. Furthermore, the emission wavelengths can be gradually modulated by the control of the steric hindrance between the adjacent substituted phenyl rings. Thus, through a comparative and detailed study of the (1)H NMR, electrochemical and photophysical properties of DSF-IFs 1 and 2, we have evidenced the intramolecular π-π interactions occurring between the two "aryl-fluorene-aryl" moieties in the ground state and in the excited state. These properties have been finally correlated to the spectacular conformational change modeled by density functional theory (DFT) calculations. Indeed, the two "aryl-fluorene-aryl" moieties switch from a staggered conformation in the ground state to an eclipsed conformation in the first excited state.

Section: Resultsmentioning

confidence: 99%

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

Métivier

et al. 2011

114

“…As it is known that the oxidation of pstacked systems is more facile than their non-stacked analogues, [58,72,73] it is reasonable to assign the second oxidation of (2,1-a)-DSF-IF to the face-to-face fluorene dimer. Analogous observations highlighting interactions between two stacked aryl moieties, have been previously reported for dibenzobicycloA C H T U N G T R E N N U N G [4.4.1]undecane [72] and for different p-systems including among others naphthalene units bridged by biphenyl linkages, [73] various oligofluorene derivatives [58,60] or porphyrins dimers. [74] We also note that the oxidation of a fluorene p-dimer reported by Rathore and co-workers occurs at about 1.42 V/SCE.…”

Section: A C H T U N G T R E N N U N Gmentioning

confidence: 99%

(2,1‐a)‐Indenofluorene Derivatives: Syntheses, X‐ray Structures, Optical and Electrochemical Properties

Rault‐Berthelot

et al. 2010

112

Two novel fluorophores based on the (2,1-a)-indenofluorenyl backbone, dispiro[fluorene-9,11'-indeno[2,1-a]fluorene-12',9''-fluorene], (2,1-a)-DSF-IF and 11,12-dihydroindeno[2,1-a]fluorene (2,1-a)-IF have been prepared through original and efficient synthetic approaches. After consideration of synthetic features, the structural, optical and electrochemical properties of these new blue/violet emitters have been studied in detail by a combined experimental and theoretical approach. The properties of the (2,1-a)-DSF-IF and (2,1-a)-IF are also compared to those of their corresponding positional isomers based on the (1,2-b)-indenofluorenyl backbone and those of related dispirofluorene heteroacenes.

“…Indeed, the first oxidation potential of (2,1-a)-DST-IF (1.12 V) is lower than the first oxidation potential of (1,2-b)-DST-IF (1.29 V). It is known that the oxidation of p-stacked systems is more facile than that of their non-stacked analogues, [39,73] and the cofacial arrangement of the two terfluorenyl units in (2,1-a)-DST-IF is hence at the origin of its observed low oxidation potential. Therefore, the first oxidation process of (2,1-a)-DST-IF may be assigned to the oxidation Figure 7.…”

Section: A C H T U N G T R E N N U N Gmentioning

confidence: 99%

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

Rault‐Berthelot

et al. 2011

Two novel terfluorenyl derivatives, 2,2'',7,7''-tetrakis(9,9-dioctyl-9H-fluoren-2-yl)dispiro[fluorene-9,11'-indeno-(2,1-a)-fluorene-12',9''-fluorene] ((2,1-a)-DST-IF) and 2,2'',7,7''-tetrakis(9,9-dioctyl-9H-fluoren-2-yl)dispiro- [fluorene-9,6'-indeno-(1,2-b)-fluorene-12',9''-fluorene] ((1,2-b)-DST-IF) have been synthesized by two different synthetic approaches. These terfluorenyl derivatives possess a different central indenofluorene core, namely (2,1-a)-indenofluorene or (1,2-b)-indenofluorene, which imposes two distinct geometry profiles, and different structural environments for the terfluorenyl fluorophores that translates into drastically different optical and electrochemical properties for (2,1-a)-DST-IF and (1,2-b)-DST-IF. These properties have been carefully studied through a combined experimental and theoretical approach. The (2,1-a)-DST-IF isomer has been successfully used as emitting layer in a blue single-layer small-molecule organic light-emitting diode (SMOLED) and appears as the first example of a blue emission arising from intramolecular terfluorenyl excimers. Regarding the importance of terfluorenyl derivatives in organic electronics, the present structure-properties relationship study, may open new avenues in the design of efficient blue fluorophores.