Mapping Acid‐Catalyzed Deprotection in Thin Polymer Films: Fluorescence Imaging Using Prefluorescent 7‐Hydroxycoumarin Probes

Abstract

Summary: Fluorescent images that illustrate acid‐catalyzed tert‐butoxycarbonyl (tBoc) deprotection patterns in polymer films were obtained using fluorescent sensors based on 7‐hydroxycoumarin dyes. Three commercial 7‐hydroxycoumarins, which are highly fluorescent, become practically nonemissive upon protection of the 7‐hydroxyl position with tBoc. In thin polymer films, the protected “prefluorescent” probes can return to their deprotected, fluorescent states by reaction with catalytic amounts of photogenerated acid and mild heating.Protected probes become highly fluorescent after acid‐induced deprotection.magnified imageProtected probes become highly fluorescent after acid‐induced deprotection.

Red–Yellow Fluorescence Patterning of a Polymer Film Containing Phthalimido Carbamate Groups

“…These include protonation induced by a photoacid generator, [6,9,12,15,16] as well as chemical amplification catalyzed by a photoacid generator. [3,[17][18][19][20][21][22] Most of these preparation methods are based on photogenerated acids, although other methods precluding the use of photoacid generators have also been reported such as the photobleaching of fluorescent polymers. [7,13,14,23,24] Photobase generators are a group of compounds that produce a base upon irradiation.…”

Photoimaging and Lithographic Processes in Polymers

“…In Scheme 12.8, we present a selection of acid sensors employed both in solution and in films [18,34,37,39,40].…”

“…A more convenient way of detecting and quantifying the acid formed is in situ, using fluorescent pH sensors that clearly mark the areas where the acid was formed [18,36,[38][39][40][41][42]. These sensors are introduced into the photoresist that is spin coated, then following exposure they image the areas where acid is formed.…”

“…12.2 shows how the acid formation is determined in situ by employing a pH sensor that changes its spectroscopic properties upon protonation. Coumarin derivatives bearing a t-Boc protecting group dramatically shift their absorption and emission maxima upon deprotection catalyzed by acid [18,40,42]. For example, Frenette et al developed a prefluorescent sensor, a Coumarin 4 derivative, which mimics the t-Boc polymer [40].…”

“…Coumarin derivatives bearing a t-Boc protecting group dramatically shift their absorption and emission maxima upon deprotection catalyzed by acid [18,40,42]. For example, Frenette et al developed a prefluorescent sensor, a Coumarin 4 derivative, which mimics the t-Boc polymer [40]. The hydroxyl functionality in 7-hydroxy-coumarins was protected with t-Boc groups that quench the fluorescence of the molecule.…”