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Fumihito Mohri
qzg00677@nifty.com

Recently, I have had to calculate T1-S0 energy differences for phosphorescence
emission spectra (0-0 bands) of some aromatic coumpounds. Then, at first,
I have tried the calculations for known compounds, using the following methods.
 (A)  Delta E(T1-S0)=E(T1,T1)-E(S0,S0), where E(T1,T1) stands for T1 state energy
    at optimized T1 geometry and E(S0,S0) S0 state energy at optimized S0 geometry.
(B) Delta E(T1-S0)=E(T1,T1)-E(S0,T1), where E(T1,S0) stands for S0 state energy at
  optimized T1 structure. This method is based on Frank-Condon principle.
(C) Delta E(T1-S0)s were calculated by TDDFT, using optimized S0 geometries.
Here, the level of theory is B3LYP/6-31G(d,p). The results in eV are listed in
 the following Table. The observed data are taken from R. S. Becker, eTHEORY AND
 INTERPRETATION OF FLUORESENCE AND PHOSPHORESCENCE',John Wiley&Sons,Inc. 1969.
                 A       B      C        obs.
Benzene          3.88    3.31    3.80     3.66
Naphtalene       2.72    2.30    2.73     2.64
Antracene        1.81    1.50    1.80     1.85
2Me-Antracene    1.81    1.46    1.83     1.81
Carbazole        3.35    3.29    3.19     3.04

Before calculations,I expected that B  would bring the results which are closest
to the observed values, because when emission of T1->S0 occurs the molecular
geometry should be kept as one for T1. However, B result is worst among them.
Moreover, I am surprised with the fact that A and C gives the results close to
observed ones. Then, I have a question. Why B bring bad results and why A and C
bring good results ?


Thanks in advance,
Fumihito Mohri