Intriguing photophysical aspects of nitro substituted 2-(2′-hydroxyphenyl)benzothiazole (HBT) derivative: AIE in non-polar media?

A novel fluorescent probe with a phosphofluorene molecular structure for selective detection of hydrogen sulfide in living cells

Hydrogen sulfide (H2S) gas plays a significant role in biological regulation. With advancements in technology, H2S has been discovered across diverse fields, necessitating a comprehensive understanding of its physiological functions through monitoring changes in H2S within complex environments and physiological processes. In this study, we designed a phosphofluorene-based conjugate probe PPF-CDNB with an asymmetric π-conjugated phosphine structure and utilized dinitrophenyl ether as the recognition site for H2S. PPF-CDNB exhibited exceptional resistance to interference and demonstrated stability over a broad pH range (3.0-10.0), making it suitable for various environmental conditions. Intracellular experiments revealed that PPF-CDNB effectively monitored both endogenous and exogenous levels of H2S.

Interrogating the nature of aggregates formed in a model azine based ESIPT coupled AIE active probe: stark differences in photodynamics in the solid state and aggregates in water

A novel Schiff base 4-bromo-2-((E)-((E)-(1-(naphthalen-2-yl)ethylidene)hydrazono)methyl)phenol (BNHMP) was synthesized and characterized by NMR, ESI-MS, FTIR and single crystal X-ray diffraction studies. In the solution phase, BNHMP shows prominent emission from the keto-form, a consequence of excited state intramolecular proton transfer (ESIPT). The quantum yield and excited state lifetime decrease in polar solvent THF compared to relatively non-polar solvent DCM. Interestingly, in aqueous solution (pH 7.0), the quantum yield along with the excited state lifetime undergoes tremendous increment. Dynamic light scattering experiments and FESEM reveal the formation of aggregates in water as reflected by the increased hydrodynamic radius of BNHMP in water. Hence, aqueous phase studies revealed BNHMP to be an AIE active probe. On the other hand, BNHMP shows huge emission intensity in the solid state. Interestingly, the emission decay behavior of BNHMP changes upon excitation, as BNHMP shows very broad absorption in the solid state. Upon excitation at 360 nm, a triexponential decay pattern is found, which changes to a biexponential one upon excitation at 450 nm. Meticulous analysis of the fluorescence lifetimes led to the assignment of J and H aggregates coexisting in the solid state with the former dominating the photodynamics. A judicious comparison of the lifetime behavior in the solid state to that in water leads to the conclusion that BNHMP undergoes AIE by the formation of J and H aggregates to an equal extent, a phenomenon starkly different from the solid-state scenario. The current results hold significance as this is among a few reports where such comprehensive spectrodynamic dissection has been performed for an ESIPT-AIE active Schiff base in solution as well as in the solid phase, thereby giving a holistic vision of the nature and fate of aggregation occurring in such azine based systems and subsequently advancing the understanding of such systems in terms of their photo behavior.

Fluorescent Organic Lewis-Pair Nanoparticles: Excited-State Intramolecular Proton Transfer Molecule 2-(2'-Hydroxyphenyl)benzothiazole Undergoes GSIPT Reactions To Be a Solid-State Nanoemitter

The excited-state intramolecular proton transfer (ESIPT) reaction, one of the fundamental photochemical processes, is known to occur in 2-(2'-hydroxyphenyl)benzothiazole (HBT), showing an enol-to-keto phototautomerization. In this article, Lewis-pair adduct formation is demonstrated between HBT (Lewis base) and diphenylborinic anhydride (DPBA; Lewis acid), in which the proton transfer occurs in the ground state to form the keto tautomer of HBT. The HBT/DPBA Lewis-pair adduct exhibits strong pale-blue fluorescence at 480 nm in dichloroethane. Additionally, organic Lewis-pair nanoparticles of HBT/DPBA are successfully synthesized on the basis of a reprecipitation protocol in which HBT in conjunction with DPBA dissolved in acetone was rapidly injected into water under ultrasonication. DPBA here also acts as a stabilizing or protecting agent to form spherical nanoparticles with well dispersion. The nanoparticles also exhibit strong keto-type emission centered at 490 nm, changing the emission color to bluish-green. Quantum chemical calculations find the sole formation of the keto tautomer of HBT counterpart in the Lewis pair. Importantly, the present synthesis methodology based on Lewis acid-base chemistry does not require complicated operations to organically synthesize solid-state emitters and thus will play a key role in simply controlling the emission behavior for the new type of organic nanoparticles.