Photophysical and structural properties of the fluorescent nucleobase analogues of the tricyclic cytosine (tC) family
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Fundamental insight into the unique fluorescence and nucleobase-mimicking properties of the
fluorescent nucleobase analogues of the tC family is not only vital in explaining the behaviour of
these probes in nucleic acid environments, but will also be profitable in the development of new
and improved fluorescent base analogues. Here, temperature-dependent fluorescence quantum
yield measurements are used to successfully separate and quantify the temperature-dependent and
temperature-independent non-radiative excited-state decay processes of the three nucleobase
analogues tC, tCO and tCnitro; all of which are derivatives of a phenothiazine or phenoxazine
tricyclic framework. These results strongly suggest that the non-radiative decay process
dominating the fast deactivation of tCnitro is an internal conversion of a different origin than the
decay pathways of tC and tCO. tCnitro is reported to be fluorescent only in less dipolar solvents at
room temperature, which is explained by an increase in excited-state dipole moment along the
main non-radiative decay pathway, a suggestion that applies in the photophysical discussion of
large polycyclic nitroaromatics in general. New insight into the ground and excited-state potential
energy surfaces of the isolated tC bases is obtained by means of high level DFT and TDDFT
calculations. The S0 potential energy surfaces of tC and tCnitro possess two global minima
corresponding to geometries folded along the middle sulfur–nitrogen axis separated by an energy
barrier of 0.05 eV as calculated at the B3LYP/6-311+G(2d,p) level. The ground-state potential
energy surface of tCO is also predicted to be shallow along the bending coordinate but with an
equilibrium geometry corresponding to the planar conformation of the tricyclic framework, which
may explain some of the dissimilar properties of tC and tCO in various confined (biological)
environments. The S1 equilibrium geometries of all three base analogues are predicted to be
planar. These results are discussed in the context of the tC bases positioned in double-stranded
DNA scenarios.
| Original language | English |
|---|---|
| Journal | Physical Chemistry Chemical Physics |
| Volume | 12 |
| Issue number | 31 |
| Pages (from-to) | 8881 |
| Number of pages | 8,892 |
| ISSN | 1463-9076 |
| DOIs | |
| Publication status | Published - 2010 |
- Faculty of Science
Research areas
ID: 17085527