jo300051v_si_001.pdf (1.6 MB)
Heavy Atom Free Singlet Oxygen Generation: Doubly Substituted Configurations Dominate S1 States of Bis-BODIPYs
journal contribution
posted on 2012-05-18, 00:00 authored by Selin Duman, Yusuf Cakmak, Safacan Kolemen, Engin U. Akkaya, Yavuz DedeS0, S1, and T1 states
of various
orthogonal 8,8′ and 8,2′-bis-boradiaza-s-indacene (BODIPY) dyes, recently (Angew. Chem., Int. Ed. 2011, 50, 11937) proposed as heavy
atom free photosensitizers for O2(1Δg) generation, were studied by multireference quantum chemical
approaches. S0→S1 excitation characteristics
of certain bis-BODIPYs are shown to be drastically different than
the parent BODIPY chromophore. Whereas a simple HOMO→LUMO-type
single substitution perfectly accounts for the BODIPY core, S1 states of certain orthogonal bis-BODIPYs are described as
linear combinations of doubly substituted (DS) configurations which
overall yield four electrons in four singly occupied orbitals. Computed
DS character of S1, strongly correlated with facile 1O2 production, was presumed to occur via S1→T1 intersystem crossing (ISC) of the sensitizer.
Further confirmation of this relation was provided by newly synthesized
BODIPY derivatives and comparison of spectroscopic properties of their
dimers and monomers. Near-IR absorption, desired for potential photodynamic
therapy applications, was not pursuable for bis-chromophores by the
standard strategy of π-extension, as DS singlet states are destabilized.
Decreased exchange coupling in π-extended cases appears to be
responsible for this destabilization. Comparisons with iodine incorporated
bis-BODIPYs suggest that the dynamics of 1O2 generation via DS S1 states are qualitatively different
from that via ISC originating from heavy atom spin–orbit coupling.
Although red-shifting the absorption wavelength to enter the therapeutic
window does not seem attainable for orthogonal bis-BODIPYs with DS
S1 states, modifications in the chromophore cores are shown
to be promising in fine-tuning the excitation characteristics.
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Keywords
T 1 statesDS S 1 statesorthogonalDoubly Substituted Configurations Dominate S 1 Statesphotodynamic therapy applicationsBODIPY coreHeavy Atom Free Singlet Oxygen Generationparent BODIPY chromophoreDecreased exchangemultireference quantum chemical approaches1 O 2 productionDS singlet statesHOMOISCS 1 statesexcitation characteristics1 O 2 generationspectroscopic propertiesComputed DS characterabsorption wavelengthBODIPY derivativeschromophore cores
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