Synthesis and Optical Properties of Excited-State Intramolecular Proton Transfer (ESIPT) Emitters with Sulfobetaine Fragments

Abstract

This article describes the synthetic efforts towards the solubilization of organic fluorescent emitters based on a 2-(2’-hydroxybenzofuranyl)benzazole (HBBX) scaffold in aqueous media under physiological conditions (PBS, pH 7.4). These dyes...

Sterically Hindered 2‐(2’‐Hydroxyphenyl)benzoxazole (HBO) Emitters: Synthesis, Spectroscopic Studies, and Theoretical Calculations

“…Moreover, for HBO‐3‐Mes and HBO‐3,5‐Tip , an additional third band is observed, located between E* and K * leading to a triple emission (Figure 3b). Based on previous reported studies on the photophysics of related HBO derivatives, this band can be unambiguously ascribed to the deprotonated species D * , originating from a competitive deprotonation process in the excited state [22,27,33] …”

“…Based on previous reported studies on the photophysics of related HBO derivatives, this band can be unambiguously ascribed to the deprotonated species D*, originating from a competitive deprotonation process in the excited state. [22,27,33] All calculated photoluminescent calculated quantum yields (PLQY) lie within the same range as the HBO reference, i. e. 1-6 % in toluene and 1-3 % in ethanol, highlighting the absence of interaction between the HBO core and the hindered phenolic substitution. It is worth noting that HBO-3,5-(tolyl) 2 appears to be the brightest in the series (QY = 11 % in toluene).…”

“…The dual emission profile is only observed in ethanol, as it is well-known that protic solvents are able to stabilize excited enol tautomers through intermolecular H-bonding interactions in ESIPT structures. [33] In toluene, all dyes display a single K* band whose maximum emission wavelength spans from 499 to 524 nm, depending on substitution, with the exception of HBO-3,5-(tolyl) 2 (λ em = 550 nm) (Table S2). These data are in alignment with the emission of unsubstituted HBO (λ em = 499 nm), consistent with the absence of rotation owing to the presence of mesityl or tip substitution at the 3, 5 or 3,5 position of the phenol.…”

“…After photoexcitation in the lower energy band (λ exc =310–350 nm), an intense emission is observed, consisting of one or two emission bands, corresponding to the single decay of K * or dual E * /K * species (Figure 3a and Figure 3b). The dual emission profile is only observed in ethanol, as it is well‐known that protic solvents are able to stabilize excited enol tautomers through intermolecular H‐bonding interactions in ESIPT structures [33] …”