Intersystem crossing to excited triplet state of aza analogues of nucleic acid bases in acetonitrile.
Excited state characteristics of aza analogues of nucleic acid bases, 8-azaadenine (8AA), 5-azacytosine (5AC), 8-azaguanine (8AG), and 6-azauracil (6AU), in acetonitrile solution were comprehensively investigated with steady state absorption and emission spectra, transient absorption measurements, emission measurements for the singlet oxygen molecule, and time-dependent density functional theory (TD-DFT) calculations. The triplet-triplet absorption spectrum of 8AA whose peak was 455 nm was observed for the first time. Sensitized singlet oxygen formation of 8AA was also observed in O(2)-saturated acetonitrile with quantum yields of 0.15 +/- 0.02. It was concluded that there were two kinds of aza analogues of nucleic acid bases: type A had substantial quantum yield for the intersystem crossing and potential of O2 (1Delta(g)) formation (8AA and 6AU), and type B did not (5AC and 8AG). TD-DFT calculations indicated that type A molecules had a dark 1npi* state below the first allowed 1pipi* state, while both S1 and S2 states for type B molecules had a pipi* character. It strongly suggested that the dark 1npi* state below the 1pipi* state would play an important role in the ISC process of aza analogues of nucleic acid bases.
Department of Chemistry and Materials Science, Tokyo Institute of Technology, 2-12-1 Ohokayama, Meguro-ku, Tokyo 152-8551, Japan.
Takashi
T
Kobayashi
Hikaru
H
Kuramochi
Yosuke
Y
Harada
Tadashi
T
Suzuki
Teijiro
T
Ichimura
D000042:Absorption; D000097:Acetonitriles / Q000737:chemistry*; D000225:Adenine / Q000031:analogs & derivatives / Q000737:chemistry; D001372:Aza Compounds / Q000737:chemistry*; D001375:Azaguanine / Q000737:chemistry; D003596:Cytosine / Q000031:analogs & derivatives / Q000737:chemistry; D009696:Nucleic Acids / Q000737:chemistry*; D011789:Quantum Theory; D026082:Singlet Oxygen / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013057:Spectrum Analysis; D014498:Uracil / Q000031:analogs & derivatives / Q000737:chemistry
D000097:Acetonitriles; D001372:Aza Compounds; D009696:Nucleic Acids; D012997:Solvents; D026082:Singlet Oxygen; C039854:5-azacytosine; D014498:Uracil; D003596:Cytosine; C100248:azauracil; D000225:Adenine; D001375:Azaguanine; C006654:8-azaadenine; C032159:acetonitrile