Blue-Emitting 2-(2'-Hydroxyphenyl)benzazole Fluorophores by Modulation of Excited-State Intramolecular Proton Transfer: Spectroscopic Studies and Theoretical Calculations.

This article describes the synthesis, spectroscopic studies, and theoretical calculations of nine original fluorophores based on the 2-(2'-hydroxyphenyl)benzazole (HBX) scaffold, functionalized at the 4-position of the phenol ring by ethynyl-extended aniline moieties. HBX dyes are well-known to display an excited-state intramolecular proton transfer (ESIPT) process, owing to a strong six-membered hydrogen bond in their structure that allows for an enol/keto tautomerism after photoexcitation. Appropriate electronic substitution can perturb the ESIPT process, leading to dual fluorescence, both excited tautomers emitting at specific wavelengths.

Impact of Heteroatom Substitution on Dual-State Emissive Rigidified 2-(2'-hydroxyphenyl)benzazole Dyes: Towards Ultra-Bright ESIPT Fluorophores*.

2-(2'-Hydroxyphenyl)benzazole (HBX) fluorophores are well-known excited-state intramolecular proton transfer (ESIPT) emitters largely studied for their synthetic versatility, photostability, strong solid-state fluorescence and ability to engineer dual emission, thus paving the way to applications as white emitters, ratiometric sensors, and cryptographic dyes. However, they are heavily quenched in solution, due to efficient non-radiative pathways taking place as a consequence of the proton transfer in the excited-state. In this contribution, the nature of the heteroring constitutive of these rigidified HBX dyes was modified and we demonstrate that this simple structural modification triggers major optical changes in terms of emission color, dual emission engineering, and importantly, fluorescent quantum yield.

Synthesis of Nitro-Aryl Functionalised 4-Amino-1,8-Naphthalimides and Their Evaluation as Fluorescent Hypoxia Sensors.

Fluorescent sensors are a vital research tool, enabling the study of intricate cellular processes in a sensitive manner. The design and synthesis of responsive and targeted probes is necessary to allow such processes to be interrogated in the cellular environment. This remains a challenge, and requires methods for functionalisation of fluorophores with multiple appendages for sensing and targeting groups.

Natural Born Laser Dyes: Excited-State Intramolecular Proton Transfer (ESIPT) Emitters and Their Use in Random Lasing Studies.

A series of five excited-state intramolecular proton transfer (ESIPT) emitters based on a 2-(2'-hydroxyphenyl) benzoxazole (HBO) scaffold, functionalized with a mono-or bis-(trialkylsilyl) acetylene extended spacer are presented. Investigation of their photophysical properties in solution and in the solid-state in different matrix, along with ab initio calculations gave useful insights into their optical behavior. Random lasing studies were conducted on a series of PMMA doped thin films, showing the presence of stimulated emission above the threshold of pumping energy density (ρth ≈ 0.

A theoretical elucidation of the mechanism of tuneable fluorescence in a full-colour emissive ESIPT dye.

BTImP, 2-(1,3-benzothiazol-2-yl)-4-methoxy-6-(1,4,5-triphenyl-1H-imidazol-2yl)phenol, a compound showing a very unusual excited state intramolecular proton transfer (ESIPT) process, is theoretically studied. Composed of two ESIPT centres, BTImP presents a switching of the ESIPT from one moiety to the other by acidic stimulation, allowing emission of a large panel of colours. In this work, the switching mechanism and its impact on the structural and optical properties are investigated with time-dependent density functional theory (TD-DFT) and post Hartree-Fock methods [ADC(2) and CC2] including the environment by considering bulk solvation effects and the important impact of the counter-ion (BF, ClO, and Cl).

First-principles investigation of the double ESIPT process in a thiophene-based dye.

The unusual emission spectrum of 2,5-bis(benzoxazol-2-yl)thiophene-3,4-diol (BBTP) is investigated. The complexity of the emission spectrum of this dye is due to the presence of two excited-state intramolecular proton transfer (ESIPT) sites that give rise to three non-equivalent tautomers. The different maxima were experimentally attributed to the initial double enol form, the single ESIPT enol-keto tautomer, and the double ESIPT structure.

An extended excited-state intramolecular proton transfer (ESIPT) emitter for random lasing applications.

An original molecular fluorophore displaying single keto (K*) excited-state intramolecular proton transfer (ESIPT) emission is presented in this article. Substitution at the 3 and 5 positions of the phenol ring of a 2-(2'-hydroxyphenylbenzoxazole) (HBO) dye by triethylsilyl-ethynyl fragments leads to a drastic enhancement of fluorescence in the solution-state as compared to unsubstituted analogues. This intense fluorescence emission is also retained in a protic solvent like ethanol and in the solid-state as embedded in a potassium bromide pellet or as 1% doped in a poly(methyl methacrylate) (PMMA) film.