Fluorescent Silica Hybrid Film-Forming Materials Based on Salicylaldazine

Alina Raditoiu,Valentin Raditoiu,Florentina Monica Raduly,Adriana Nicoleta Frone,Georgiana Cornelia Ispas,Luminita Eugenia Wagner,Raluca Manea,Mihai Anastasescu,Violeta Purcar

doi:10.3390/coatings10121255

Alina Raditoiu, Valentin Raditoiu + Show 7 more

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https://doi.org/10.3390/coatings10121255

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Abstract

Fluorescent film-forming materials were obtained by embedding salicylaldazine (SAA) in silica hybrids generated by sol–gel processes from different silane precursors in acid catalysis. Tuned local environments for the fluorophore were generated in the hosting network by modifying silica sols with organic groups through the co-condensation of tetraethylortosilicate (TEOS) and different alkoxysilanes hydrolysis products. The photophysical properties of the luminescent hybrid films were studied in direct relationship with structural, textural, and surface properties and based on interactions between SAA species and the silica hosting network. Film-forming materials were studied in order to determine differences in absorption and fluorescence emission due to the environments around the fluorophore. The variations recorded in the fluorescence emission spectra of the hybrid films were related to interactions established between the fluorophore species and their sterically hindered surroundings of the host hybrid silica, where free molecular motions are restricted. The influence of the type and amount of network modifier and of the fluorophore loading on the transparency of the films and fluorescence intensity was also investigated. The study carried out led to the elucidation of the necessary conditions for obtaining luminescent film-forming materials with high luminescence intensity and transparency useful for the design of new light concentrators.

Highlights

Salicylaldazine and several analogs were intensively studied due to their fluorescent properties [1,2,3]
Since excited state based on intramolecular proton transfer (ESIPT) emission is highly sensitive to local surroundings and the presence of hydrogen bond-donating species can lead to inhibition of the process, this type of fluorophores is widely used for the detection of chemical or biological targets [4]
The fluorophore is obtained using a method already presented in the literature [9]

Summary

Introduction

Salicylaldazine and several analogs were intensively studied due to their fluorescent properties [1,2,3]. This type of fluorophores owes their special optical properties, such as strong solid state luminescence and tunable emission, to the environment-sensitive excited state based on intramolecular proton transfer (ESIPT) mechanism, which is responsible for the luminescence. Dyes exhibiting this type of luminescence mechanism can be used as sensors, fluorescent tracers in biology, in electroluminescent devices, laser dyes [3], etc. Since ESIPT emission is highly sensitive to local surroundings and the presence of hydrogen bond-donating species can lead to inhibition of the process, this type of fluorophores is widely used for the detection of chemical or biological targets [4].

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