Synthesis of and Fluorescent Imaging with a Polymer Having t-BOC-Protected Quinizarin Moieties

Abstract

The generation of patterned images in polymer films has been extensively studied and used in fundamental and applied research areas. The development of patterned color or fluorescent images, especially, is of great technological importance in the electronics industry. Recently, the generation of functional images by selective immobilization of organic dyes in the polymer film has been reported. [1±3] Selective removal of acid-labile protecting groups through photoinduced chemical transformation followed by chemisorption of organic dyes from solution into the patterned polymer film has given micrometer-scale functional images. The two-step procedures described in the literature, however, have potential problems such as difficulty of dye penetration into polymer matrices and concern about longterm stability of the patterned images.To avoid these limitations, we have tried to develop a direct method of generating fluorescence images with a precursor molecule. The strategic basis for designing a precursor is that the precursor molecule is non-fluorescent and/or colorless, but becomes fluorescent and/or reveals color by photoinduced chemical changes. We have previously reported that the UV absorption maximum and fluorescence of quinizarin 1 can be readily altered and manipulated simply by blocking the intramolecular hydrogen bonds. [4] Thus, the UV absorption maximum (479 nm) of quinizarin 1 shifts to a shorter wavelength (335 nm) on blocking the two phenols with two tert-butoxycarbonyl (t-BOC) groups. In addition, the t-BOC-protected quinizarin 2 has virtually no fluorescence, whereas quinizarin 1 is strongly fluorescent due to the quasi-aromatic structure caused by intramolecular hydrogen bonding. As a part of our continuing interest in the generation of relief and functional images with transiently protected precursor molecules in polymer films, we now report the synthesis of a novel polymer having t-BOC-protected quinizarin moieties and the genera-tion of color and fluorescent images by photolithographic methods. To our knowledge, this is the first example of finely resolved fluorescent images with a polymer having transiently protected precursor pendants.The strategies employed for the synthesis of t-BOC-protected quinizarin monomer 7 are shown in Scheme 1. Aldol condensation of leucoquinizarin (3) with 5-(benzyloxy)pentanal (4) [5] in the presence of piperidinium acetate in 2-propanol under Marschalk conditions [6] readily afforded the key intermediate, 2-substituted quinizarin 5, in an excellent yield (96 %). The intermediate 5, obtained as a pale red solid, has strong fluorescence due to intramolecular hydrogen bonding, confirming the proposed structure. Protection of the two phenol groups of 5 with di-tert-butyl dicarbonate in the presence of a catalytic amount of 4-dimethylaminopyridine (DMAP) in tetrahydrofuran (THF) provided the t-BOC-protected 2-substituted quinizarin 6 in 92 % yield. The fluorescence is virtually eliminated in the t-BOC-protected intermediate 6 and the position of the UV absorp-[**] We...

The “Precursor Approach” to Patterned Fluorescence Images in Polymer Films

“…The disadvantage of this type of three component imaging system is that mixtures of the t-Boc-protected quinizarin 2 and a polymer, such as PMMA, can undergo phase separation after long periods of time. One way to make the system based on t-Boc-protected 2 more suitable for practical applications involves the incorporation of the precursor in the fluorescing chromophore into the polymer chain as a pendant group, [29,30] as exemplified by precursor containing polymer 3 ( Figure 6). In order to generate patterned fluorescence images with 3, only a photoacid generator is required, since the precursor containing polymer can be readily spin-coated on the solid substrate without the use of additional matrix polymers.…”

“…[70][71][72][73] Owing to this intriguing light driven molecular switching phenomenon, photochromic compound have been extensively investigated as key materials in optical memory, switching and sensor devices. Azobenzene (28), [74] spiropyran (29) [75] phenoxyquinone (30) [76] and bisthienylethene (31) [77] derivatives are representative photochromic compounds (Scheme 14). These molecules undergo various types of structural isomerization reactions, such as cis-trans isomerization (azobenzene), ring opening (spiropyran), phenyl group migration (phenoxyquinone) or ring closure (bisthienylethene), upon UV irradiation.…”

Transient protection of intramolecular hydrogen bonding: A simple but elegant approach for functional imaging

“…In order to avoid the intrinsic problems associated with the two-step procedures described above, we [10][11][12][13] and other groups [14][15][16][17][18] have developed direct methods of generating color or fluorescence images in the polymer film without the wet-developing processes. We, especially, focused on the generation of functional images using the 'precursor approach'.…”

“…In recent preliminary studies, we reported on the generation of color/fluorescent images with t-Boc-protected quinizarin dye precursors using above starateges. 10,12,13 Here we present comprehensive characterization of the precursor approaches based on transient protection of intramolecular hydrogen bonding for the functional images in the polymer film.…”

The first synthesis of a transition metal-catalyzed homopolymer having pendentt-boc-protected quinizarin for patterned fluorescence images

“…This is mainly because most transition metal catalysts rapidly react with functional groups and become inactive for polymerization. As part of our on going efforts for the development of photoinduced color/fluorescence changing polymers, [13][14][15][16][17][18][19] we now report the first successful transition metal-catalyzed synthesis of norbornene-derived homopolymers having pendent t-Boc-protected quinizarin moieties for patterned fluorescence images.…”