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Title: Tryptanthrin from indigo: Synthesis, excited state deactivation routes and efficient singlet oxygen sensitization
Authors: Pinheiro, Daniela 
Piñeiro, Marta 
Pina, João 
Brandão, Pedro 
Galvão, Adelino M.
Melo, J. Sérgio Seixas de 
Keywords: Indigo; Tryptanthrin; Fluorescence; Singlet oxygen sensitization; TDDFT
Issue Date: Apr-2020
Publisher: Elsevier
Project: info:eu-repo/grantAgreement/RCUK/Innovate UK/103252/GB/HYLIGHT – HYbrid LIquefied petroleum Gas tanker witH magspliT 
info:eu-repo/grantAgreement/POCI-01-0145-FEDER-016387/SunStorage - Harvesting and storage of solar energy 
Serial title, monograph or event: Dyes and Pigments
Volume: 175
Issue: 108125
Abstract: The microwave-assisted synthesis of tryptanthrin from indigo in mild oxidation conditions, and a comprehensive study of the excited state properties of this compound in a variety of solvents with different polarity and viscosity values at room and low temperatures are reported. In contrast with indigo, emission of the triplet state of tryptanthrin is observed with a very efficient singlet oxygen sensitization quantum yield, indicating that the triplet state is efficiently populated. From time-resolved fluorescence and femtosecond transient absorption data, further supported with time-dependent density functional theory (TDDFT) calculations, two species, with S1 states with locally excited (LE) of π,π* nature and a charge transfer (CT) of n,π* characteristics, originated from an initially populated Frank-Condon S2 state (π,π*), are observed. The two electronically independent species are energetically nearly degenerate and inter-conversion is predicted (and rate constants determined) to occur between LE (S1) and CT (S1) species. Due to the low value of the fluorescence quantum yield (~10−3) and high triplet state yield (ϕT≥ϕΔ), the high stability of this compound is associated to the high efficiency of the radiationless deactivation processes which involve the formation of the CT state which efficiently converts, through S1 ~~> Tn intersystem crossing, to the T1 triplet state.
ISSN: 01437208
DOI: 10.1016/j.dyepig.2019.108125
Rights: embargoedAccess
Appears in Collections:I&D CQC - Artigos em Revistas Internacionais

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