화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.110, No.13, 4320-4328, 2006
Solvent and linker influences on AQ(.-)/dA(.+) charge-transfer state energetics and dynamics in anthraquinonyl-linker-deoxyadenosine conjugates
The goal of this work is to produce high yields of long-lived AQ(center dot-)/dA(center dot+) charge transfer (CT) excited states (or photoproducts). This goal fits within a larger context of trying generally to produce high yields of long-lived CT excited states within DNA nucleoside conjugates that can be incorporated into DNA duplexes. Depending upon the energetics of the anthraquinoryl (AQ) (3)(pi,pi*) state as well as the reduction potentials of the subunits in particular anthraquinonyl-adenine conjugates, CT quenching of the AQ 3(pi,pi*) state may or may not occur in polar organic solvents. In MeOH, bis(3',5'-O-acetyl)-N'-(anthraquinone-2-carbonyl)-2'deoxyadenosine (AQCOdA) behaves as intended and forms a (3)(AQ(center dot-)/dA(center dot+)) CT state with a lifetime of 3 ns. However, in norpolar THF the AQ(center dot-)/dA(center dot+) CT states of AQCOdA are too high in energy to be formed, and in DMSO a (1)(AQ(center dot-)/dA(center dot+)) CT state is formed but lives only 6 ps. Although the lowest energy excited state for AQCOdA in MeOH is a (3)(AQ(center dot-)/dA(center dot+)) CT state, for N-6-(anthraquinone-2-methylenyl)-2'-deoxyadenosine (AQMedA) in the same solvent it is a (3)(pi,pi*) state. Changing the linking carbonyl in AQCOdA to Methylene in AQMedA makes the anthraquinonyl subunit harder to reduce by 166 mV. This raises the energy of the (3)(AQ(center dot-)/dA(center dot+)) CT state above that of the (3)(pi,pi*) in AQMedA. The conclusion is that anthraquinonyl-dA conjugates will not have lowest energy AQ(center dot-)/dA(center dot+) CT states in polar organic solvents unless the anthraquinonyl subunit is also substituted with an electron-withdrawing group that raises the AQ-subunit's reduction potential above that of AQ. A key finding in this work is that the lifetime of the 3(AQ(center dot-)/dA(center dot+)) CT excited state (ca. 3 ns) is ca. 500-times longer than that of the corresponding 1(AQ(center dot-)/dA(center dot+)) CT excited state (ca. 6 ps).