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

Abstract

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.

Electron-Deficient Dihydroindaceno-Dithiophene Regioisomers for n-Type Organic Field-Effect Transistors

“…Electronwithdrawing ketones and/or dicyanovinylene functionalities have been introduced on the bridgeheads to ensure a low LUMO energy level and hexyl chains have been attached on the two side-thiophene cores for processability and crystallinity. 54 The synthetic strategies developed herein are based on the same approach involving in a first step the synthesis of the corresponding ketones meta-IDT(=O) 2 and para-IDT(=O) 2 . Thus, the synthesis of meta-IDT(=O) 2 has been envisaged through an efficient route (Scheme 1, A) based on the intramolecular electrophilic bicyclization of the 2,2'-(1,3-phenylene)dithiophene core, 2.…”

“…Thus, after the two successive reduction processes, the quinonoidal dianions were obtained. 62 From the onset reduction potentials respectively measured at -0.83 and -0.84 V for para-IDT(=O) 2 and meta-IDT(=O) 2 , we determined their LUMO energy levels lying at -3.57…”

“…These LUMO energy levels appear to be deep and highlight the strong electronwithdrawing character of the ketones groups. Thus, the deep LUMO energy levels of both molecules lead to a short electrochemical energy gap ∆E el of 2.05 eV for para-IDT(=O) 2 and 2.19 eV for meta-IDT(=O) 2 . It is noteworthy that the difference between the two gaps comes from the restriction of conjugation in the meta isomer compared to its para isomer and is therefore clearly induced by the modulation of the HOMO levels and hence by the nature of the π−conjugated system.…”

“…The exponential development of organic electronic leads to an always growing demand of new, highly efficient organic semiconductors (OSCs) adapted to their use in specific devices 1 including organic light-emitting diodes (OLED) based on fluorescent emitting materials, [2][3][4][5][6][7][8] or based on phosphorescent materials, [9][10][11][12][13][14][15][16][17][18][19] organic field-effect transistor (OFET) [20][21][22][23][24] or organic photovoltaic (OPV). 1,25 Historically, in the field of OFETs, the design of p-type materials (hole-transporting) such as pentacene, 26 oligothiophene 27 or bridged oligoarylene [28][29] 33 (see 1-4 structures in Chart 1).…”

Synthesis and Properties of Annulated 2-(Azaar-2-yl)- and 2,2'-Di(azaar-2-yl)-9,9'-spirobifluorenes

“…2D and DEPT NMR experiments and comparison with the NMR data of the parent 9,9'-spirobifluorene [29] and related compounds reported previously [23,25] allowed us to assign all the proton resonances of the products, which are summarized in Table 1. Some proton resonances were characteristic enough to provide a probe for the suggested structure.…”