Ultra‐High‐Density Photochromic Main‐Chain 1,2‐Dithienylcyclopentene Polymers Prepared Using Ring‐Opening Metathesis Polymerization

Abstract

Photochromic molecules based on 1,2-bis(3-thienyl)cyclopentene derivatives undergo reversible photocyclization reactions between their colorless open-ring, 1o, and colored closed-ring, 1c, forms (see structures below) with an impressive degree of fatigue resistance and thermal irreversibility. [1] The photoreactions can be accompanied by changes in useful physical properties other than absorbance, including refractive index, [2] luminescence, [3] electronic conductance, [4] viscosity, [5] and optical rotation. [6] The photomodulation of these properties has the potential to significantly advance optoelectronic technologies.In order to fully exploit these versatile compounds they must be incorporated into forms that can be easily processed, such as films, which necessitates the development of photoresponsive polymers. [7] Ring-opening metathesis polymerization (ROMP) is an ideal method for preparing functional polymers due to its mild reaction conditions and its compatibility with a wide range of functional groups. [8] We have recently capitalized on this versatility by generating several photoresponsive polymers (2, see structure below) where the photochromic element is attached to the polymer's backbone. [9] Although many of these novel polymers contain an impressive 68 wt.-% of the photoactive dithienylethene, a further increase in the content of the photochromic component will produce ultrahigh-density polymers that will be beneficial in optoelectronic applications.Higher densities can be achieved by decreasing the size of the linker that connects the dithienylethene to the polymer backbone. A better approach takes advantage of the fact that ROMP of strained bicyclic dienes produces cyclopentene rings, analogous to the way bicyclic alkenes generate cyclopentane derivatives. This strategy results in the incorporation of the central ring of the photochromic 1,2-bis(3-thienyl)cyclopentene directly into the polymer backbone. Here we report the first lipophilic and hydrophilic main-chain photochromic homopolymers 5a±c prepared using ROMP. [10] Synthesis of the key dichloride monomer 4a is achieved in a single step by cross-coupling the zinc salt of 3-bromo-5-chloro-2-methylthiophene [11] 3 with 2,3-dibromobicyclo-[2.2.1]hepta-2,5-diene, [12] as shown in Scheme 1. [13] The scheme also illustrates how monomer 4a can be converted to the corresponding diester 4b. Polymers 5a and 5b are then prepared with typical ROMP conditions using commercially COMMUNICATIONS

Molecular Structure Analysis of Photochromic Diarylethene

“…Taking the advantage of the fact that ROMP (Ringopening methathesis polymerization) of strained bicyclic dienes produces cyclopentene rings, monomer in which the bridging unit is a bicyclic dienes was synthesized as shown in scheme 10 [27]. The ROMP reaction of the strained olefin produces the requisite cylcopentene backbone; hence, an ultra-high-density (93% w/w) photochromic main chain 1,2-dithienylcyclopentene polymer was prepared.…”

High‐Content Photochromic Polymers Based on Dithienylethenes

“…In a recent article we have prepared a family of main-chain DTE polymers 11 by incorporating the cyclopentene directly into the polymer backbone using ROMP technology. [35] Our approach takes advantage of the fact that ROMP of strained bicyclic dienes produces cyclopentene derivatives, analogous to the way bicyclic alkenes generate cyclopentane derivatives. This strategy results in the incorporation of the central ring of the DTE unit directly into the polymer backbone and produces high-content homopolymers (93 wt.-%) in good yield, with narrow polydispersities (1.3-1.4), and that display efficient photochromism both in solution and the solid-state (Figure 8).…”

Electrochromism of photochromic diarylethene derivative

“…Diarylethene derivatives have been known as one of the most promising photochromic molecules for their potential applications as rewritable optical data storage media. So far considerable interests have been focused on photochromic diarylethenes for their high conversion efficiencies of reversible photochromic reactions, excellent thermal stability of both isomers, and good fatigue resistance, which are attractive features for application in optical storage and as molecule switches [4][5][6][7][8][9][10][11][12][13][14].…”