Applications of Endoperoxides derived from Acenes and Singlet Oxygen

Abstract

Abstract Under simple conditions of aerobic irradiation, acenes can undergo an oxygenation to endoperoxides (EPOs). Mechanistic studies disclosed that this reaction can proceed either along a concerted or an ionic stepwise pathway, strongly controlled by peripheral substituents. For many acenes the process is either thermally or photochemically reversible and oxygen is released either in its ground or excited state. Evidence was found that some EPOs reconvert along a concerted pathway and others along a stepwise path with radical intermediates. Thus, the yields of released singlet oxygen ( 1 O 2 ) and the amount of decomposition products vary. Highly reversible formations of acene EPOs found applications as photochromic systems and as the basis to generate erasable two‐dimensional pattern structures into thin films on surfaces. Irreversible reactions were applied to release “caged” molecules from an acene based photolinker and to initiate polymerizations either from cationic or radical precursors. More recently, EPOs of diarylanthracenes were employed as stages of molecular rotary switches. Due to the rapid formation of acene EPOs, probes were designed to detect 1 O 2 with high sensitivity. Many acenes suit as carriers of singlet oxygen via EPOs and special emphasis is devoted to water soluble systems used in biologic media. EPOs were encapsulated into hosts like cyclodextrines, proteins or rotaxanes as well. These systems exhibit interesting properties in terms of molecular recognition. Due to the convenient and reversible formation of acene EPOs and their release of 1 O 2 , many applications towards surface patterning or antitumor therapy might emerge during the next years.