Dithienylethene, structurally

Another interesting example of a photoresponsive polymer based on the dithienylethene structure is polyAuorene 33, which can be synthesized by a Suzuki coupling reaction [69]. This polymer contains a... 

A huge variety of 1,2-diheteroarylethenes undergo photochemical 67t-electrocyclization, and much of this literature, particularly that of the photochromic reactions of l,2-bis(methylthienyl)- and 1,2-bis(methylbenzothiophen-3-yl)-perfluorocyclopentenes, is reviewed elsewhere in this Handbook.However, examples of these systems are presented here to illustrate the diversity of the molecular architectures that undergo this type of photochemical process. A variety of compounds derived from the basic 1,2-dithienylethene structure (e.g., 45) undergo photochemical closure/ring opening in solution, films, and... 

The terms diarylethenes, dithienylethenes, and dihetarylethenes, as applied to the structures of photochromic products II, of course, do not strictly meet the nomenclature requirements. However, these terms have gained wide acceptance in the special literature. The classification of compounds containing heterocycles as bridges is also rather arbitrary. 

An alternative method for dithienylperfluorocyclopentenes is based on the functionalization of the presynthesized dithienylethenes having, as a rule, very simple structures. Scheme 4 shows a part of the synthetic route (the assembly of unique photochrome 7 performed by Lehn and coworkers) by a Suzuki reaction starting from available boronic acids 6 (96CEJ1399). This reaction is widely used for the modification of the dihe-tarylethene moiety by aromatic substituents. This scheme also gives the reverse example of the synthesis of 9, where the boronic acid fragment is present in 8 (07JPP(A)202). 

Recently, a ternary complex for a signal transmission system has been constructed by Aida and his co-workers [36], It involved three movable components a biaryl derivative bearing four zinc porphyrins (2), a pyridine-appended dithienylethene derivative (1), and a chiral tetrasubstituted ferrocene (3 ), as illustrated by its structure (Scheme 8). The three components were interconnected with bidentate coordination bonds. Component 2 was the bridge between 1 and 3. The well-designed triad was built up by multi-step reactions through routine methods. 

Fig. 1.13 a Structures of bi-UPy photochromic dithienylethene 45 and mono-UPy-terminated fluorescent dye FI b Depiction of the energy transfer (ET) process of the thin film spin coated from solutions of 97 3 4S-F1 under UVA is irradiation, (green open form of 45 purple closed form of 45 yellow FI) Reproduced from Ref. [112] by permission of John Wiley Sons Ltd... 

Fig. 6.9 a Molecular structure of a nematic GLC (30) with a dithienylethene core undergoing ring closure and opening with irradiation at 365 and 577 nm, respectively, and b reversible photochromism using a 4-pm-thick film at room temperature. Used with permission [45]... 

Fig. 11.20 Structures of the poly(bithenylene-phenylene)s, Poly-9, and (/f)-/(S)-Poly-10 having dithienylethene (DE) moieties in open form and closed form upon exposure to Vis and UV light, respectively...

It is of interest that the polymers show CPL as well as CD in cast films, although they show neither CPL nor CD in solution, except the weak CD signal that corresponds to the overlapped absorption bands of the dithienylethene and phenylene linked with the chiral alkyl moiety. The formation of helical 7t-stacking structures of Poly-10 is supported by the observation of its CPL in cast films, as shown in Fig. 11.23. The open forms of (lf)-/(S)-Poly-10 show negative and... 

Interconvertible formation of open-/closed-rings in dithienylethene architecture with different spectral characteristics by UV-Vis irradiation make them attractive as photochromic materials (see Chapter 21). It was recently demonstrated that this reversible switching can be used for smart light-controlled carrier switch in multi-layer OLEDs [193], The photochromic emissive material 140 shows a large difference in ionization potentials between the open and closed structures (6.1 and 5.3 eV, respectively) and only has a HOMO level high enough to support the hole transport. Consequently, introducing 140 in the multilayer... 

With the polymer chemical industry being the largest of its kind and the enormous impact of polymers on our daily life, the incorporation of photochromic dyes as dopants in polymeric matrices or as integral components in the polymeric structure is highly desirable. In this section, we discuss how photoresponsive dithienylethenes can be integrated with polymer science by briefly describing both polymer structure and materials processing. We will include in our discussions homopolymers, random copolymers and molecular dopants and will start with the last case after a brief mention of some requirements. 

In this section, we have examined several examples of dithienylethene derivatives that are suitable for dispersing in polymer matrices and processing into thin Aims. Although this approach to solid-state photoresponsive materials is convenient, it is limited by the amount of compound that can be incorporated into the matrix before segregaAon occurs. In Aie next secAon, we will explore how this limitaAon can be circumvented by integraAng Aie compounds directly into the polymer structure to produce high-content solid-state materials [65]. 

The unusual photochromic properties of thiophene derivatives are the subject of the review by Neil Branda and co-workers in Chapter 21. It is truly amazing to see the diversity of the molecular and polymer structures, and the range of photochromic properties, accessed by modification of a single building block, dithienylethene. 

Krayushkin MM, Vorontsova LG, Uzhinov BM (2001) The structure and characteristics of photochromic dithienylethenes. Int J Photoenergy 3 25-32... 

Recently, spiropyran-initiated hyperbranched polyglycerol (SP-hb-PG) micelles were reported [70]. These carriers responded to UV/visible light and could dissociate due to conversion of the hydrophobic chromophore SP to zwitterionic and hydrophilic merocyanine (ME). In addition, chromophores such as coumarin, o-nitrobenzyl, stilbene, dithienylethene and 2-diazo-l,2-napthoquinone (DNQ) have been employed in light-responsive micelles, which can respond either to UV/ visible or NIR irradiation to undergo structural or phase changes and trigger the drug release from micelles [71-74]. 

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