Luminescence of oxotetrahydrobenzo[c]phenanthridine in polar and nonpolar solvents: Inversion of the energy levels of the Sππ* and Tnπ* states |
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Authors: | S L Bondarev V N Knyukshto S A Tikhomirov and A N Pyrko |
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Institution: | (1) Institute of Molecular and Atomic Physics, Belarussian Academy of Sciences, Minsk, 220072, Belarus;(2) Institute of Bioorganic Chemistry, Belarussian Academy of Sciences, Minsk, 220141, Belarus |
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Abstract: | The spectral-luminescent properties and electronic-level structure of a derivative of oxotetrahydrobenzoc]phenanthridine—3,3-dimethyl-1,2,3,4-tetrahydrobenzoc]phenanthridine-1-one
(DTP)—in polar and nonpolar solutions are studied by the luminescence and picosecond spectroscopy techniques at 293 and 77
K. It is shown that DTP exhibits ππp* fluorescence only in polar proton-containing methanol, ethanol, and n-propanol and that this fluorescence is associated with a chromophore + alcohol complex. Solutions of DTP in n-propanol and the nonpolar mixture methylcyclohexane + toluene (6:1) at 77 K display ππp* phosphorescence with a quantum yield
ΦPh=0.1, a lifetime τPh=1.9 s, and a frequency of the 0-0 transition equal to 21550 cm−1. The fact that DTP fluorescence is absent in aprotic solvents and exists in alcohols is explained by the inversion of the
energy levels of the S
ππ* and T
n
π* states, as a result of which the energy level of the fluorescing S
ππ* state in alcohol becomes the lowest. The picosecond spectra and kinetics of the inducedS
n
(ππ*) ← S
1(π π*) and T
k
(ππ*) ← T
1(ππ*) absorption made it possible to estimate the lifetime of the S
1(ππ*) state of DTP in n-propanol at 293 K (20±10 ps) and the position of the triplet-triplet absorption peak (495 nm).
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Translated from Optika i Spektroskopiya, Vol. 94, No. 6, 2003, pp. 993–998.
Original Russian Text Copyright ? 2003 by Bondarev, Knyukshto, Tikhomirov, Pyrko. |
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Keywords: | |
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