The heavy-atom effect on xanthene dyes for photopolymerization by visible light

Abstract

Heavy halogen atoms on the xanthene ring significantly increase the photoredox catalytic performance for visible-light-induced photopolymerization.

Photoinitiated Free‐Radical Polymerization of 4,5,6,7‐Tetrahalogenated Fluoresceins

“…For example, fluorescein, the most representative xanthene dye, is synthesized through the simple condensation of resorcinol and phthalic anhydride in the presence of an acid catalyst at 85 °C [10] . Fluorescein exhibits excellent molar absorptivity (ϵ>92,000 cm −1 ⋅ M −1 ) about 494 nm and fluorescein quantum yield (Φ f >0.9) in an alkaline aqueous solution [11,12] . Furthermore, the photophysical and redox properties of xanthene dyes can be readily tuned by selecting a suitable core structure and deliberately introducing various types of substituents [13,14] .…”

“…Furthermore, the photophysical and redox properties of xanthene dyes can be readily tuned by selecting a suitable core structure and deliberately introducing various types of substituents [13,14] . In particular, rhodamine and fluorescein derivatives bearing halogenated xanthene core ring exhibit redshifted absorption and emission bands at the maximum wavelength compared with the fluorescein [12] . Moreover, xanthene dyes can be versatile fluorogenic probes by incorporating a ligand to a specific target via synthetic methodologies [15–17] …”

“…After the photoinduced electron transfer (PET) between the 3 Dye* and amine, open‐shell intermediates such as dye radical anion and amine radical cation are generated [29] . The dye radical anion can be regenerated to the dye through electron transfer from molecular oxygen, and the amine radical cation loses a proton, followed by the initiation of radical reactions [12] …”

Emerging Organic Photoredox Catalysts for Organic Transformations

“…Recently, the heavy atom effect on the ISC efficiency of xanthene dyes for visible‐light mediated photopolymerization in xanthene/trialkylamine system was studied by Lee, Lee, and co‐workers . A high catalyst loading ensures rapid reaction but hampers biological application at the same time.…”

Highly Effective Sensitizers Based on Merocyanine Dyes for Visible Light Initiated Radical Polymerization

“…The systems included acridine and xanthene dyes. Since then, many other dyestuffs have been designed as photosensitizers [6] that extend the spectral range of the photopolymerization to the visible region [7][8][9][10][11][12][13][14] because this light is cheap, safe and possesses higher penetration in comparison to UV light [15].…”