Photochemistry of a 9‐Dithianyl‐Pyronin Derivative: A Cornucopia of Reaction Intermediates Lead to Common Photoproducts

Abstract

Leaving groups attached to the meso‐methyl position of many common dyes, such as xanthene, BODIPY, or pyronin derivatives, can be liberated upon irradiation with visible light. However, the course of phototransformations of such photoactivatable systems can be quite complex and the identification of reaction intermediates or even products is often neglected. This paper exemplifies the photochemistry of a 9‐dithianyl‐pyronin derivative, which undergoes an oxidative transformation at the meso‐position to give a 3,6‐diamino‐9H‐xanthen‐9‐one derivative, formic acid, and carbon monoxide as the main photoproducts. The course of this multi‐photon multi‐step reaction was studied under various conditions by steady‐state and time‐resolved optical spectroscopy, mass spectrometry and NMR spectroscopy to understand the effects of solvents and molecular oxygen on individual steps. Our analyses have revealed the existence of many intermediates and their interrelationships to provide a complete picture of the transformation, which can bring new inputs to a rational design of new photoactivatable pyronin or xanthene derivatives.

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

“…Many intermediates in this process were identified and their interrelationships were clarified using steady-state and timeresolved optical spectroscopy, mass spectrometry, and NMR spectroscopy. 765 Scheme 43 presents a simplified mechanism for this complex reaction, which involves at least three lightinitiated steps. A different mechanism involving photooxidative cleavage by singlet oxygen was observed for the photolysis of exo-alkylidene xanthenes.…”

“…Recently, Klán, Roithová, and co-workers subsequently showed that transformation of 141 is a multi-photon multi-step process. Many intermediates in this process were identified and their interrelationships were clarified using steady-state and time-resolved optical spectroscopy, mass spectrometry, and NMR spectroscopy Scheme presents a simplified mechanism for this complex reaction, which involves at least three light-initiated steps.…”

Photochemistry of Common Xanthene Fluorescent Dyes as Efficient Visible-light Activatable CO-Releasing Molecules

“…[11][12][13] It has already been demonstrated that the photochemistry of some xanthene derivatives can result in CO liberation. 14,15 Carbon monoxide (CO) is an essential biogenic gasotransmitter 16 that interacts with metalloproteins. 17,18 CO in mammalian organisms is avidly bound to hemoglobin (~80%), 19 whereas it has various regulatory and protective functions, such as protection during hypoxia, 20 vasodilatation, 21 bactericidal 22 and anti-inflammatory effects, [23][24][25] promotion of wound healing, 26 reducing tumor growth, [27][28][29] in the remaining part of plasma under physiological concentrations.…”

Common xanthene fluorescent dyes are visible-light activatable CO-releasing molecules

“…29,30 Visible light can also trigger CO liberation, e.g., from carbonyl metal complexes 33,34 or metal-free molecules. 27,[35][36][37][38] Rational design of such light absorbing xanthene 35,39 or BODIPY photoCORMs 56 allows fine-tuning of their optical and chemical properties.…”