Performance of Tris(2-methyl-8-quinolinolato)aluminum as Fluorescent Anionophore

Abstract

Sensing ions and molecules by fluorescent chemosensors is highly applicable to a wide range of technologies and has currently been studied intensively. 1,2 Lewis acid-base reactions are extensively used as a driving force for the recognition of cations, while hydrogen-bondings are mainly used for the recognition of anions. One application of the Lewis acid-base reactions to anion-sensing is the fluorometric detection of fluoride with boron-containing compounds. 3,4 The high affinity of boron to fluoride and the change in fluorescent characteristics with an increase in coordination number of boron were successfully utilized for the detection of fluoride.The group 13 metal complexes with 8-quinolinol derivatives (Hq: 8-quinolinol, Hmq: 2-methyl-8-quinolinol) have recently been attracting much attention as a component of the organic light-emitting device. The aluminum complex with a parent compound of 8-quinolinol, [Alq3], has been used as a green light-emitting material. 5 The effects of substituents on the optical performance were studied; [Al(mq)3] was reported to show a blue emission, which was ascribed to an electrondonating methyl group.6 Later, the mixed-ligand complex with Hmq and phenol (PhOH), [Al(mq)2(OPh)], has been proposed as an alternative having a higher chemical stability. 7,8 To explore the further possibility of the Lewis acid-base reactions for the fluorometric detection of anions, we have studied the reactions of these aluminum complexes ([Al(mq) Spectroscopic studiesThe solvents were dehydrated with molecular sieves; the residual water concentrations were 10 -2 mol dm -3 for DMSO and DMF and 5 × 10 -2 mol dm -3 for EtOH. -4 mol dm -3 for the others) and anions up to a molar ratio of 9 against Al were prepared, and their spectroscopic properties were evaluated. In the presence of an excess Hmq, the absorbance at 400 nm and the fluorescence at 510 nm with an excitation at 400 nm were monitored to avoid the absorption by Hmq. In the absence of any excess Hmq, the absorbance at 310 and 360 nm and the fluorescence at 480 nm with an excitation at 360 nm were also monitored.The lifetime of photoluminescence was measured with a time-resolved spectroscopic system, PTI-5100S (Photon Technology International).

Theoretical investigation on the structure and electronic properties of Alq2R (R=8-hydroxyquinoline, OH, phenolate and phenylphenolate) and its derivatives

“…The calculated results show that the DFT calculations are in better agreement with experimental data. The calculated Al-N and Al-O bond lengths differed within ±0.04 Å from the experimental values [36].…”

8-Hydroxy-2-methylquinoline

“…Aluminium derivatives of 2-methyl-8-hydroxyquinoline are light-emitting compounds. For their crystal structures, see: Iijima & Yamamoto (2006); Kushi & Fernando (1970); Rajeswaran et al (2007); Toulokhonova et al (2002); Yamaguchi et al (2002a,b); Yuchi et al (2003).…”