The excited-state behavior of four-coordinate N,C-chelate organoboron
dyes, based on arylisoquinoline ligands with varying
degree of charge-transfer character, was characterized. Data
related to excited triplet state formation, oxygen quenching,
and singlet-oxygen formation were obtained. The results jointly
rationalize the previously observed high photostability of
the dyes in air-equilibrated media. Furthermore, femtosecond
transient absorption experiments enabled the spectroscopic
visualization of the excited intramolecular charge transfer (ICT)
state that gives rise to the fluorescence of the dyes.The funding by the Spanish Ministry of Economy, Industry, and Competitiveness (grants CTQ2014-54729-C2-1-P for U.P., CTQ2014-54729-C2-2-P for F.B., CTQ2013-48164-C2-1-P, CTQ2013-48164-C2-2-P for A.R., Ramon y Cajal contract RYC-2013-12585 for A.R.), the European Union (ERDF), the Andalusian Government (grants 2012/FQM-2140 for U.P., 2009/FQM-4537 and 2012/FQM-1078 for A.R.), and the University of Huelva (postdoctoral contract for V.F.P.) is gratefully acknowledged
