Excited-State Proton Transfer from Embedded Photoacids to Silanols on Mesostructured Surfaces: Role of Structural Heterogeneity

As a common process in nature, excited-state proton transfer(ESPT)is becoming increasingly attractive due to its wide applications insmart sensors and materials. Compared with well-known ESPT in bulksolution, knowledge of ESPT between excited-state photoacids and silanolson mesostructured surfaces is still limited. Herein, we present ourwork on ESPT behavior in photoacid-embedded mesostructured CTAB-silicafilms by using steady and picosecond time-resolved fluorescence spectroscopy.Compared with ESPT in solutions, two unique characteristics of photoacid-silanolESPT were revealed: (1) deprotonated silanols act as ESPT acceptors,while protonated silanols affect ESPT by changing the basicity ofthe silica surface; (2) largely distinguished properties of Q(3)/Q(2) silanols and their non-uniform distributionon the surface lead to heterogeneous properties of the surface suchas basicity that greatly affect ESPT dynamics. Our work provides newinsight into the ESPT mechanism in mesostructured systems and inspirationfor designing smart sensors and materials that utilize the sensitivityto proton concentration.

Automated summary

In this study, the excited-state proton transfer (ESPT) behavior between photoacids and silanols on mesostructured surfaces was investigated using steady and picosecond time-resolved fluorescence spectroscopy. It was found that deprotonated silanols acted as acceptors in ESPT, while protonated silanols affected ESPT by changing the basicity of the silica surface. The non-uniform distribution of Q(3)/Q(2) silanols on the surface led to heterogeneous properties, such as basicity, which greatly influenced the ESPT dynamics. This work provides new insights into the ESPT mechanism in mesostructured systems and inspiration for designing smart sensors and materials sensitive to proton concentration.