Absorption and Emission Sensitivity of 2‐(2′‐Hydroxyphenyl)benzoxazole to Solvents and Impurities

Abstract

2-(2'-Hydroxyphenyl)benzoxazole (HBO) is known for undergoing intramolecular proton transfer in the excited state to result in the emission of its tautomer. A minor long-wavelength absorption band in the range 370-420 nm has been reported in highly polar solvents such as dimethylsulfoxide (DMSO). However, the nature of this species has not been entirely clarified. In this work, we provide evidence that this long-wavelength absorption band might have been caused by base or metal salt impurities that are introduced into the spectral sample during solvent transport using glass Pasteur pipettes. The contamination by base or metal salt could be avoided by using borosilicate glass syringes or nonglass pipettes in sample handling. Quantum chemical calculations conclude that solvent-mediated deprotonation is too energetically costly to occur without the aid of a base of an adequate strength. In the presence of such a base, the deprotonation of HBO and its effect on emission are investigated in dichloromethane and DMSO, the latter of which facilitates deprotonation much more readily than the former. Finally, the absorption and emission spectra of HBO in 13 solvents are reported, from which it is concluded that ESIPT is hindered in polar solvents that are also strong hydrogen bond acceptors.

Designing Tunable White‐Light Emission from an Aurophilic CuI/AuI Coordination Polymer with Thioether Ligands

“…Targeting new white‐light‐emitting materials has become critical due to their importance in next‐generation solid‐state lighting and display technologies, which offer a marked increase in efficiency over more traditional incandescent and compact fluorescent technologies . Single‐source white‐light materials require emissive components in the blue, green/yellow, and red regions and an absence of complicating energy transfer . For example, lanthanide‐containing coordination polymer materials have often been exploited due to their well‐defined emission colours (e.g., red from europium, green from terbium), which are blended to tune the final colour; an organic moiety is often required to provide the blue emission component .…”

Photophysical and thermal properties of novel solid state fluorescent benzoxazole based styryl dyes from a DFT study

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Fluorescence of Hydroxyphenyl-Substituted “Click” Triazoles

“…This shoulder centers at ∼365 nm, which is amplified upon addition of a base such as DBU and therefore assigned to the deprotonated 8 . The spectral susceptibility of hydroxylated aromatics to base in strongly HB-accepting solvents such as DMSO has been documented. , The adventitious base might have been introduced during sample preparation …”

“…The coumarin molecule in Figure has a moderate Stokes shift value reaching 2000 cm –1 . 4-( N , N -Dimethylamino)­benzonitrile (DMABN) − and 2-(2′-hydroxyphenyl)­benzoxazole (HBO) − are examples of compounds with large Stokes shifts that could exceed 10 000 cm –1 . DMABN and HBO operate through two distinct mechanisms that result in large Stokes shifts (see the next paragraph).…”