Understanding the Nature of the States Responsible for the Green Emission in Oxidized Poly(9,9‐dialkylfluorene)s: Photophysics and Structural Studies of Linear Dialkylfluorene/Fluorenone Model Compounds

Abstract

Here, the optical properties of a series of structurally well‐defined model compounds for oxidatively degraded poly(dialkylfluorenes) (PFs) are reported. Specifically, linear compounds comprising one, two, or four dihexylfluorene (F) moieties together with one fluorenone (O) moiety placed either at the end or in the center of each chain (i.e., FO, FFO, FOF, FFOFF) are studied. The results support the recent observation that the photophysics of the fluorenone‐centered “pentamer” (FFOFF) is most similar to that of oxidized PFs. They further demonstrate that molecule–molecule interaction is essential to activate the green emission band. Investigations by X‐ray diffraction (XRD) identify the solid‐state structure of a representative member of this class of compounds and reveal inter‐molecular interaction through dipole–dipole coupling between neighboring fluorenone moieties.

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

“…Indeed, the fluorescence spectra of 5 only display one band (l = 380 nm) for diluted solutions but display two sets of emission bands at (l = 380 nm and 540/570 nm) when increasing the concentration (see Figure S14 in the Supporting Information). On the other hand, the thin-film emission spectrum of 5 only displays one large band at 580 nm (see Figure S15 in the Supporting Information) assigned, as recently proposed by Holmes and co-workers, [54] to intermolecular interactions in the solid state between the ketones units. 4 It is hence reasonable to similarly assign the large band (540/570 nm) observed in concentrated solutions of 5 (vide supra) to intermolecular interactions between the ketone units.…”

Solid State Structure of Poly(9,9-dinonylfluorene)

“…36,37 For example, τ of the 38 which is very close to the observed torsion potential minimum at ϕ = 68°. 39 The branched side chains of PF2/6 are in the amorphous state, perhaps allowing "a more optimal" conformation of the main chain, whereas the linear side chains compete energetically and force the main chain toward a more extended state.…”

Incorporation of Spiroxanthene Units in Blue‐Emitting Oligophenylene Frameworks: A New Molecular Design for OLED Applications

“…The origin of such contributions at low energy has been extensively studied for the last decade as it remains one important problem in blue OLED technology 55. 85 Indeed, the appearance of the well‐known low‐energy emission band (also called g‐band) has been the subject of debate about its origin 85. If this low‐energy emission band was initially explained by the excimer emission (the formation of dimerized units in the excited state that emit at lower energies) due to the π–π interchromophore interactions of the main π‐system,86 it seems to be agreed nowadays that the low‐energy emission band is usually linked to the presence of keto‐defects appearing in phenylene derivatives 87.…”

“…[55,85] Indeed, the appearance of the wellknown low-energy emission band (also called g-band) has been the subject of debate about its origin. [85] If this lowenergy emission band was initially explained by the excimer emission (the formation of dimerized units in the excited state that emit at lower energies) due to the p-p interchromophore interactions of the main p-system, [86] it seems to be agreed nowadays that the low-energy emission band is usually linked to the presence of keto-defects appearing in phenylene derivatives. [87,88] Despite being still debated, one possible manner to determine whether this low-energy emission band arises from keto-defects or excimer emission due to p-p interchromophore interactions of the main p-system is to study the behavior of a DSX-LPP thin-film in the strict absence of oxygen.…”