om6b00255_si_001.pdf (5.37 MB)
Longer-Wavelength-Absorbing, Extended Chalcogenorhodamine Dyes
journal contribution
posted on 2016-05-19, 18:40 authored by Mark W. Kryman, Theresa M. McCormick, Michael R. DettyExtended
rhodamines were prepared by inserting an additional fused benzene
ring into the rhodamine xanthylium core. The synthesis of “bent”
dyes 4-E (E = S, Se, Te) began with regioselective lithiation
of the 1-position of N,N-diisopropyl
6-dimethylamino-2-naphthamide (11b) with n-BuLi/TMEDA (≥25:1 1- vs 3-lithiation) followed by addition
of a dichalcogenide electrophile. The synthesis of “linear”
dyes 5-E (E = S, Se, Te) began with regioselective lithiation
of the 3-position of N,N-diethyl
6-dimethylamino-2-naphthamide (11a) with lithium tetramethylpiperidide
(≥50:1 3- vs 1-lithiation) followed by addition of a dichalcogenide
electrophile. Dyes 4-E and 5-E have absorption
maxima in the 633–700 nm range. Dyes 4-E generate
singlet oxygen upon irradiation while dyes 4-S and 5-S are highly fluorescent, with quantum yields for fluorescence
of 0.47 and 0.18, respectively. DFT calculations were performed on
the 4-E and 5-E chromophores. For the dyes 4-E, the lowest energy excitation is due solely to the HOMO–LUMO
transition. For dyes 5-E, the lowest energy excitation
is a combination of two excitations, both having contributions from
the HOMO to LUMO and HOMO-1 to LUMO.