TY - JOUR

T1 - Photophysical and structural properties of the fluorescent nucleobase analogues of the tricyclic cytosine (tC) family

AU - Preus, Søren

AU - Kilså, Kristine

AU - Wilhelmsson, L. Marcus

AU - Albinsson, Bo

PY - 2010

Y1 - 2010

N2 - Fundamental insight into the unique fluorescence and nucleobase-mimicking properties of thefluorescent nucleobase analogues of the tC family is not only vital in explaining the behaviour ofthese probes in nucleic acid environments, but will also be profitable in the development of newand improved fluorescent base analogues. Here, temperature-dependent fluorescence quantumyield measurements are used to successfully separate and quantify the temperature-dependent andtemperature-independent non-radiative excited-state decay processes of the three nucleobaseanalogues tC, tCO and tCnitro; all of which are derivatives of a phenothiazine or phenoxazinetricyclic framework. These results strongly suggest that the non-radiative decay processdominating the fast deactivation of tCnitro is an internal conversion of a different origin than thedecay pathways of tC and tCO. tCnitro is reported to be fluorescent only in less dipolar solvents atroom temperature, which is explained by an increase in excited-state dipole moment along themain non-radiative decay pathway, a suggestion that applies in the photophysical discussion oflarge polycyclic nitroaromatics in general. New insight into the ground and excited-state potentialenergy surfaces of the isolated tC bases is obtained by means of high level DFT and TDDFTcalculations. The S0 potential energy surfaces of tC and tCnitro possess two global minimacorresponding to geometries folded along the middle sulfur–nitrogen axis separated by an energybarrier of 0.05 eV as calculated at the B3LYP/6-311+G(2d,p) level. The ground-state potentialenergy surface of tCO is also predicted to be shallow along the bending coordinate but with anequilibrium geometry corresponding to the planar conformation of the tricyclic framework, whichmay 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 beplanar. These results are discussed in the context of the tC bases positioned in double-strandedDNA scenarios.

AB - Fundamental insight into the unique fluorescence and nucleobase-mimicking properties of thefluorescent nucleobase analogues of the tC family is not only vital in explaining the behaviour ofthese probes in nucleic acid environments, but will also be profitable in the development of newand improved fluorescent base analogues. Here, temperature-dependent fluorescence quantumyield measurements are used to successfully separate and quantify the temperature-dependent andtemperature-independent non-radiative excited-state decay processes of the three nucleobaseanalogues tC, tCO and tCnitro; all of which are derivatives of a phenothiazine or phenoxazinetricyclic framework. These results strongly suggest that the non-radiative decay processdominating the fast deactivation of tCnitro is an internal conversion of a different origin than thedecay pathways of tC and tCO. tCnitro is reported to be fluorescent only in less dipolar solvents atroom temperature, which is explained by an increase in excited-state dipole moment along themain non-radiative decay pathway, a suggestion that applies in the photophysical discussion oflarge polycyclic nitroaromatics in general. New insight into the ground and excited-state potentialenergy surfaces of the isolated tC bases is obtained by means of high level DFT and TDDFTcalculations. The S0 potential energy surfaces of tC and tCnitro possess two global minimacorresponding to geometries folded along the middle sulfur–nitrogen axis separated by an energybarrier of 0.05 eV as calculated at the B3LYP/6-311+G(2d,p) level. The ground-state potentialenergy surface of tCO is also predicted to be shallow along the bending coordinate but with anequilibrium geometry corresponding to the planar conformation of the tricyclic framework, whichmay 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 beplanar. These results are discussed in the context of the tC bases positioned in double-strandedDNA scenarios.

KW - Faculty of Science

U2 - 10.1039/c000625d

DO - 10.1039/c000625d

M3 - Journal article

C2 - 20532361

VL - 12

SP - 8881

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

SN - 1463-9076

IS - 31

ER -