Due to significantly tackling the problems of aggregation-caused quenching and water insolubility, aggregationinduced emission electrochemiluminescence (AIE-ECL) has emerged as a research highlight in aqueous detection and sensing. Herein, we reported a series of cyclopentadienols featuring excellent AIE-ECL properties on the basis of an enhanced aromaticity strategy. In detail, substituents profoundly determined ECL emission by affecting the characteristic absorption peak intensity ratio in UV−vis spectra and lowest unoccupied molecular orbital (LUMO)−highest occupied molecular orbital (HOMO) energies. It was found that 1,2,3,4,5-pentafluorophenyl cyclopentadienol (PFCD) containing an electron-withdrawing fluorine substituent, the maximum R/B band ratio, and a smaller LUMO−HOMO band gap demonstrated the best ECL performance. Meanwhile, such an AIE-ECL system displayed a wide response range toward pH (4−12) with a good linear relationship. Our research not only enriched polycyclic aromatic hydrocarbon-based AIE-ECL systems but also established an efficient pH sensor in the aqueous phase.

The development of superior probes is highly desirable and valuable for viscosity measurement. Herein, we designed and reported a series of diphenylbenzofulvene (DPBF)-based organic luminophores according to the molecular regulation strategy. There are two free-rotating phenyl groups attached to the rigid fluorene skeleton in the DPBF, enabling its unique propeller-like noncoplanar chemical structure. Benefiting from this, DPBFs could feature outstanding PL and ECL emissions with intriguing aggregation-induced characteristics. Experimental and theoretical investigations revealed that substituent, spatial structure, and molecular orbital energy profoundly affected their luminescent behaviors. It was disclosed that fluoro-substituted DPBF(F)2 with a smaller LUMO–HOMO band gap demonstrated the strongest ECL emission and was selected as the optimal ECL emitter. Finally, DPBF(F)2 featured a linear response to the viscosity and VC content with lower limits of detection (LOD) of 5.69 μcP and 38.2 nM, respectively. This study represents the first example of the ECL probe toward viscosity and will be of great significance for both ECL application and viscosity measurement.

The intriguing aggregation-induced emission has recently been applied in the electrochemiluminescence, called aggregation-induced electrochemiluminescence (AIE-ECL), which is conducive to solving the water insolubility and aggregation-caused quenching for most organic luminescence probes. However, AIE-ECL still has the problems of low luminous efficiency and limited practical application. In this work, we disclosed the AIE-ECL properties of 1,2,3-triaryl-substituted indenes containing rigid structures. Experimental and theoretical investigations demonstrated that such a rigid structure could significantly enhance the aromaticity and stability and thereby the luminescence performance of these indenes. Moreover, according to the finding of hydrogen/deuterium exchange for active hydrogen in indene under electrical excitation, ultrasensitive detection for D2O in H2O was realized by such an indene-based AIE-ECL system. Our research not only provided an attractive strategy to enhance the luminescence property for an AIE-active luminophore but also established a superior sensor toward D2O.

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