Design and applications of 4-yl-(methyl)coumarins and their derivatives

Photoresponsive;coumarins;greyscale photolithography

Ritchey, Joshua A.

关键词: Photoresponsive;    coumarins;    greyscale photolithography;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/16842/1_Ritchey_Joshua.pdf?sequence=2&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Surface chemistry is a well-established area of research and is required in manycommercial applications. However, most surface modifications are static in naturemeaning a single treatment will produce a single, fixed surface state (eg: hydrophobic,hydrophilic, etc.). Dynamic systems, those that respond to stimuli, have become anactive area of surface chemistry because they provide a means to vary surfaceproperties. Responsive dynamic systems are classified as either reversible orirreversible. When light is used as a stimulus, the chemical moieties that produce thereversible and irreversible responses are known as photoswitches and photofuses,respectively.The o-nitrobenzyl photofuse, which was initially used as a biological caginggroup, has been utilized in various surface applications with great success. However,this photofuse can be problematic due to the long exposure times required for fullconversion and the reactive byproducts that form upon UV exposure. Anotherphotofuse, known as the 4-yl-(methyl)coumarin, is of particular interest because of itsrapid photochemical response, lack of reactive products upon UV exposure, and manydifferent photofuses are readily prepared from inexpensive, commercially availablestarting materials.A divergent synthetic scheme was developed that allows access to a variety ofcoumarin photofuses, via similar synthetic pathways, that enable multiple surfacemodifications. After establishing this synthetic pathway, various coumarin photofuseswere prepared and applied to surfaces to demonstrate the utility of this convenient andefficient photofuse. Prepared photofuses provide transitions including hydrophobic-to-negative, hydrophobic-to-positive, negative-to-positive, positive-to-negative, andhydrophobic-to-neutral transitions.Multiple photofuses were then utilized to probe chemical greyscaling bycombining the photoresponsive coumarin monolayer with novel greyscalephotolithography masks. The versatility of the coumarin photofuse was demonstratedthrough simple modifications of the coumarin core to provide access to characterizationtechniques such as secondary ion mass spectrometry (SIMS) and fluorescencemicroscopy. Chemical gradients were successfully patterned and characterized. Thepatterned gradients were then used to produce pressure sensitive microfluidic gatesbased on the variation in surface hydrophobicity. Correlation of mask transparency toresulting surface hydrophobicity provided a predictive curve of gating pressures thatwere in excellent agreement with theoretically predicted values.The coumarin photofuse was then utilized to pattern substrates based on thechanges in surface composition. Monolayer templating has been reported previously,but the photoresponsive nature of the coumarin monolayers reported herein providesunique patterning capabilities within three-dimensional structures such as artificial opalsby taking advantage of the photonic properties of these materials. Functionalization,photochemical conversion, and labeling within inverse opals was performed andcharacterized using confocal fluorescence microscopy. Alternative labeling andpatterning schemes were also successfully performed on planar substrates includingatomic layer deposition and selective metallization.