Handbook of Aggregation-Induced Emission, Volume 3. Группа авторов

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Название Handbook of Aggregation-Induced Emission, Volume 3
Автор произведения Группа авторов
Жанр Химия
Серия
Издательство Химия
Год выпуска 0
isbn 9781119643067



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target="_blank" rel="nofollow" href="#ulink_73fdb55d-ab45-5615-81f6-30e2f760f885">Figure 3.6 Chemical structure of TPE‐4N and fluorescence intensity changes of the AIEgen‐coated steel specimen before and after drawing at fracture under the illumination with a long‐range UV lamp.

      Owing to the OFF–ON mechanism provided by the TPE‐4N probe, the mechanochromic response was detected even at a very moderate strain of 0.13% and with a progressive enhancement up to deformations of 20%. It was reported that the green emission intensity at drawings of 65% resulted seven times higher than that of the pristine undeformed metal.

      3.3.2 Thermochromic AIE‐doped Polymer Films

      Thermochromic polymer films have been deeply investigated in the recent literature starting from thermoplastic polymer matrices containing small amounts (<5 wt.%) of physically dispersed dyes or fluorophores able to change their optical features after a temperature change above a certain threshold. The working mechanism at the base of such a system mainly consists of aggregation/deaggregation processes among the chromophoric moieties of the dispersed optical probes [13, 52]. As far as the fluorogenic response is concerned, most of the fluorophore selected experienced thermal stress by decreasing or increasing their emission intensity, thus yielding in an ACQ or aggregation‐induced enhanced emission (AIEE) phenomena [66]. Polymer matrices were reported to behave not only as a mere support for the optical probes but their thermal features in terms of melting (or crystallization) temperature and/or glass‐transition temperature can trigger optical changes in the embedded fluorophore. Therefore, thermochromic polymer films were prepared not only to develop optical sensors but also to provide useful information about the structural changes occurring in the supporting polymer matrix by changing the external temperature.

Schematic illustration of fluorescence ΦF of PS, SBS, and SBR films doped with 0.1 wt.% of TPE.

      The higher emission of the doped PS film with respect to the corresponding SBS matrix can be easily visualized by exposing the materials to the excitation of a long‐range UV lamp at 366 nm (Figure 3.7, inset). Analogously, Tang et al. proposed a similar investigation [68], also taking advantages of more sensitive AIEgens with TICT features [69], and achieved a reliable, simple, and fast method for high‐contrast visualization and differentiation of micrometer‐sized phase separation in polymer structures and blends [70]. This method was based on the RIR and on the TICT of several AIEgens, whose fluorescence features (i.e. emission intensity and wavelength) changed in different polymer phases with different rigidities and polarities. Therefore, each polymer phase can be easily labeled and promptly identified thanks to the different fluorescence intensities and wavelengths with high contrast and low background noise.

Schematic illustration of chemical structure of the TPE-functionalized PCL polymer and reversible color changes upon heating–cooling solicitations.