Preparation and photophysical properties of fluorescent difluoroboronated β-diketones having phenanthrene moieties studied by emission and transient absorption measurements

Abstract

Six difluoroboronated β-diketones having the phenanthrene skeleton (Phe@Ar) are prepared. Based on the measurements of the fluorescence quantum yields, lifetimes and transient absorption, the photophysical features of Phe@Ar are studied in comparison with those of difluoroboronated diketones having phenyl, naphthyl and anthryl moieties. β-Diketones having 1-, 2-, 3- and 9-phenanthryl moieties (PheDKAr) were prepared as the precursor to Phe@Ar. 1-Acetylphenanthrene was synthesized by the photocyclization method as the key building block of PheDKAr having the 1-phenanthryl moiety. The counter aromatic moieties (Ar) of the prepared PheDKAr are varied with phenyl, furyl and thienyl rings (Ar = Ph, F and T, respectively) to investigate the effects of π-conjugation on the fluorescence properties. The prepared Phe@Ars are fluorescent with appreciable fluorescence quantum yields which depend on the substitution position of the phenanthrene moiety. 3-Phe@Ph having the 3-phenanthryl moiety provides the largest fluorescence quantum yield (0.81) in acetonitrile among the Phe@Ars whereas 2-Phe@Ph having the 2-phenanthryl moiety shows the smallest fluorescence quantum yield (0.07) in acetonitrile. All the Phe@Ars show fluorescence also in the solid state, and the fluorescence spectra and quantum yields were determined. Transient absorption measurement using laser flash photolysis of the Phe@Ars revealed the triplet formation. DFT and TD-DFT calculations of Phe@Ars rationalize the dependency of the fluorescence quantum yields on the substitution position of the phenanthrene skeleton in terms of difference in the oscillator strength for the HOMO-LUMO transition.

Methoxy‐Substituted Difluoroboron Benzoylacetonate Complexes with Color‐Tunable Phosphorescence

“…In previous reports, our group has explored the effects of π‐conjugation,, heteroaromatic groups, and heavy‐atom placement . Recently, other groups have reported additional substituents, such as phenanthrene, chrysene, amines, and more . In particular, Cano and co‐workers have also observed advantages in brightness and color‐tuning with alkoxy donors on BF 2 bdk dyes ,.…”

Unique Solid‐State Emission Behavior of Aromatic Difluoroboronated β‐Diketones as an Emitter in Organic Light‐Emitting Devices

“…The BF3DK derivatives, 3-Phe@F, 3-Phe@Ph,a nd 2-Flu@Ph were prepared according to literature procedures. [7,8] NPD and TCTA were purchased from eRay.m CP was purchased from Lumtec. DPEPO, [14] and DBT-TRZ [15] and B3PyPB [16] were synthesized according to literature procedures.…”

“…Severala ttempts have been made to increaset he h PL value by modifying the aromatic ligand. [6][7][8] For example, Fraser and co-workersr eportedt he photophysical features of BF 2 DK with avobenzone as al igand (BF 2 AVB). [2] Electron-donor substituents, such as methoxy and tert-butyl groups, were introduced at the aromatic substituents and achieving very high h PL valueso f9 0% in dichloromethane.…”

“…Recently,w edeveloped p-extended BF 2 DK derivatives with h PL values of up to 96 %b ys ubstituting the phenyl group with fluorene, anthracene, and phenanthrene moieties in solution. [7,8] More recently,I keda and co-workers reported the formationo fu nique "excited multimer" BF 2 DK derivatives depending on the molecular aggregation state in the single crystals. [9] Although tremendous efforts have been devoted to investigating BF 2 DK derivatives in the solids tate (such as single crystals and polymerd ispersion films), their application in organic solid-state electronic devices,s uch as organic lightemitting devices( OLEDs), is almostu nexplored.…”

“…A fundamental BF 2 DK with dibenzoylmethane ( Ph@Ph ), which has two phenyl groups as the ligand, exhibited a photoluminescent quantum efficiency ( η PL value) of less than 50 %. Several attempts have been made to increase the η PL value by modifying the aromatic ligand . For example, Fraser and co‐workers reported the photophysical features of BF 2 DK with avobenzone as a ligand ( BF 2 AVB ) .…”