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Fumihito Mohri

qzg00677@nifty.com

Dear All,

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

Sat Feb 6 '10 2:36pm

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