Organic Letters
Letter
DMSO displayed a much broader emission (300−580 nm)
Notes
with a red-shifted (ca. 18 nm) emission maximum at λ = 460
em
The authors declare no competing financial interest.
nm, besides a high energy emission band at around 397 nm.
Both the absorption and emission maximum of 1 is red-shifted
when compared to those of simple 4-hydroxycoumarin, 7-
ACKNOWLEDGMENTS
■
P.V. acknowledges DST-SERB (SB/S1/OC-47/2014), India,
for financial support. P.K. is thankful to CSIR for a SRF. Dr.
Babu Varughese and Dr. P. K. Sudhadevi Antharjanam of SAIF
facility at IIT Madas are thanked for X-ray data collection and
help with the structure solution. We thank Dr. R. Baskar,
Department of Chemistry, IIT Madras, for help with DOSY
measurements.
3
3
methoxy-4-hydroxycoumarin, precursor macrocycle 1a
8
(
Table 1) and calix[4]naphthalene. This indicates that the
visible blue emission arises from the coumarin unit of the
macrocycle 1; the role of heteroaromatic pyranone unit is
clearly evident. The visible blue emission from 1 in solution can
be attributed to a large Stokes shift of 132−168 nm. Notably,
fluorescent dyes with large Stokes shifts are excellent candidates
34
for super-resolution optical microscopy. The photolumines-
cence (PL) quantum yields (Φ) of 1 measured in polar aprotic
solvents, such as chloroform and DMSO, are 0.16 and 0.09,
respectively, which is far higher than the simple 7-methoxy-4-
DEDICATION
■
Dedicated to Prof. S. Sankararaman on the occasion of his 60th
birthday.
33
hydroxy- and 4-methylcoumarins. The decrement of the
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