Advances in Spiropyrans/Spirooxazines and Applications Based on Fluorescence Resonance Energy Transfer (FRET) with Fluorescent Materials

Abstract

Studies on the following were reviewed: (1) the structure of spiropyrans and spirooxazines (two kinds of spiro compounds) under external stimuli and (2) the construction and applications of composite systems based on fluorescence resonance energy transfer (FRET) with fluorescent materials. When treated with different stimuli (light, acids and bases, solvents, metal ions, temperature, redox potential, and so on), spiropyrans/spirooxazines undergo transformations between the ring-closed form (SP), the ring-opened merocyanine (MC) form, and the protonated ring-opened form (MCH). This is due to the breakage of the spiro C–O bond and the protonation of MC, along with a color change. Various novel, multifunctional materials based on photochromic spiropyrans and spirooxazines have been successfully developed because of the vastly differently physiochemical properties posssed by the SP, MC and MCH forms. Among the three different structural forms, the MC form has been studied most extensively. The MC form not only gives complexes with various inorganic particles, biological molecules, and organic chemicals but also acts as the energy acceptor (of energy from fluorescent molecules) during energy transfer processes that take place under proper conditions. Furthermore, spiropyran and spirooxazine compounds exhibit reversible physicochemical property changes under proper stimuli; this provides more advantages compared with other photochromic compounds. Additionally, the molecular structures of spiropyrans and spirooxazines can be easily modified and extended, so better compounds can be obtained to expand the scope of already known applications. Described in detail are: (1) the structural properties of spiropyrans and spirooxazines and related photochromic mechanisms; (2) composite systems based on spiropyrans and spirooxazines, and (3) fluorescent materials which have potential applications in sensing, probing, and a variety of optical elements.

Color Performance, Durability and Handle of Inkjet-Printed and UV-Cured Photochromic Textiles for Multi-Colored Applications

“…Spirooxazines are more rigid with a higher molecular weight and more non-planar in structure in their colorless state [22]. However, upon isomerization spirooxazines become more or less planar and polar [23][24][25]. As can be seen in Figure 4 for the factor dye, RR disposes of stronger ΔK/S and higher switching rates k col and k decol .…”

Photochromic films prepared by solid state processing of disentangled ultrahigh molecular weight polyethylene and photochromic dyes composites

“…The photo‐induced opening of spiro‐ring, resulted excited singlet state by generation of ring opened intermediate, which consequently results various short‐lived isomers. The lifetimes of the short‐live intermediates are in the range of 10 −8 –10 −3 s in solution state 33 . In general, two aromatic rings maintain an orthogonal orientation in closed ring form.…”

Near infrared light‐induced disassembly of polymeric micelles based on methylene blue conjugated polyethylene glycol

“…14,15 Accordingly, biomedical applications of photoresponsive phenomenon have been exemplified by various newly developed molecules which upon exposure to NIR light irradiation will experience chemical changes, which include metal-based ruthenium complexes (bond cleavage, 700 nm), 10,16 chlorophyll (heat generation, 700 nm), 17 phthalocyanine (singlet oxygen generation, 700 nm), 18 and spiropyran (isomerization, 650 nm). 19 Recently, methylene blue (MB) with a 10-N-carbamoyl linkage was reported by our research group as a 660 nm NIR photocleavable ligand. 20 This finding was suggested to hold significant potentials in chemical and biomedical applications such as NIR photolabile protecting moiety, phototriggered release dual-drug hybrid, and photoresponsive materials for drug delivery systems.…”