Expanding π‑Conjugation in Chlorins Using Ethenyl Linker

• Published in: Journal of organic chemistry 2018-08, Vol.83 (16), p.9076-9087
• Main Authors: Meares, Adam, Bhagavathy, Ganga Viswanathan, Zik, Shannon R, Gallagher, Thomas, Ptaszek, Marcin
• Format: Article
• Language: English
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/acs.joc.8b01186

A series of chlorin monomers and dyads has been prepared to probe the effect of ethenyl vs ethynyl linkers on the electronic conjugation and optical properties in resulting derivatives. Styryl-substituted chlorins have been prepared either by a Heck reaction or by microwave-assisted olefin metathesis, while β–β ethenyl-linked dyads have been synthesized from the corresponding vinyl-substituted chlorin monomer using microwave-assisted olefin metathesis. It has been found that when an ethenyl linker is connected at the β-position of chlorin it provides stronger electronic conjugation than an ethynyl one, which is manifested by a greater bathochromic shift of the longest wavelength absorption (Q y ) and emission bands. Stronger electronic coupling is particularly evident for dyads, where ethenyl-linked dyad exhibits a strong near-IR absorption band emission (λabs = 707 nm, λem = 712 nm, Φf = 0.45), compared to the deep-red absorption and emission of a corresponding ethynyl-linked dyad (λabs = 689 nm, λem = 691 nm, Φf = 0.48). The reactivity of ethenyl-linked dyads with singlet oxygen is discussed as well. The results reported here provide further guidelines for molecular design of deep-red and near-IR absorbing and intensely emitting chlorin derivatives and chlorins with extended π-electronic conjugation for a variety of photonic applications.