Fluorescent J-Aggregates and Their Biological Applications - Advanced Fluorescence Reporters in Chemistry and Biology - page 150

the above mentioned aggregates demonstrated strong CD band and thus were
considered to be formed on DNA. The fluorescence quantum yield of the J-aggre-
gates formed on DNA was equal to 0.05, while for the dye monomers in aqueous
solution this value was 0.018, and for the DNA-bound dye monomer 0.44. Upon
DNA addition, the maximum J-aggregate absorption was observed for DNA to dye
concentrations ratio 7.0 4.0. A further increase of DNA concentration leads to

destruction of aggregates and to binding of dye monomers to DNA.
The studies of carbocyanine dye Cyan

iPr (Fig. 7 ) in the presence of DNA [ 38 ]
showed that in absorption spectrum, together with the band corresponding to the
dye monomer bound to DNA, the long-wavelength band connected with the dye
J-aggregates was present. As this band was not manifested in the absence of DNA,
the aggregates were supposed to be formed on DNA. Moreover, the studies of the
dye in the presence of double-stranded synthetic polynucleotides revealed that the
GC-containing polynucleotides do not induce aggregate formation. At the same
time, the addition of AT-containing species resulted in the appearance of pure
J-aggregate spectrum that contained two bands, both shifted to the long-wavelength
region as compared to the monomer one (Fig. 8 ). The studied aggregate demon-
strated rather intense fluorescence (Fig. 8 ) with quantum yield of about 0.05 that is
50 times higher than that of free dye and close to that of the dye monomer bound to
AT-containing polynucleotide [ 39 ]. The fluorescence excitation anisotropy study
revealed the presence of significant angle between the dipole moments of the two
allowed J-aggregate absorption transitions, pointing on Davydov splitting in the
structure of excited energy levels of J-aggregate [ 20 ]. It was supposed that the
aggregate is formed in DNA minor groove (Fig. 9 ), and the dipole moments of its

b

450 500 550 600 650 700 750

0.6 600

x 10 times

0.5 500

0.4 400

0.3 300

0.2 200

0.1 100

0.0 0

450 500 550 600 650 700 750

wavelength, nm

Fig. 8 Absorption ( left ) and fluorescence ( right ) spectra of 10 5 M Cyan b iPr in buffer ( dashed )
and of 3 10 5 M b.p. poly(dA)-poly(dT) ( solid lines ).

Free dye fluorescence spectrum intensity is multiplied ten times [ 40 ]

10 5 M Cyan

b iPr in presence of 3.5