9,10-Phenanthrenequinone（PQ） and benzil are important a-diketones. This manuscript explains the first comparison of PQ and benzil molecular properties. We have used 1H NMR, 13C NMR, 1H-IH COSY, HMBC, HMQC, UV-Vis absorption and emission, CV and TGA experiments to study PQ and benzil that provided the following novel results. （1） The 1H NMR（CDC13） of PQ show δ 8.19（H1）, 8.02（H4）, 7.72（H3）, 7.47（H2） instead of an earlier reported 8.25（H4）, 8.08（H1）, 7.80（H2）, 7.55（H3）; （2） in the 13C NMR（CDCl3）, the C9/C10（C=O） signal of PQ appears upfield（6 180.3） compared to C9/Cl0（C=O） signal of benzil（6 194.5）, which shows higher electrophilic character（more attractive for nucleophiles） of C9/C10（C=O） of benzil; （3） the first 2max for the UV-Vis absorption and emission of PQ are blue-shifted compared to benzil despite increased conjugation attributed to the different symmetries（C2v for PQ and C2h for Benzil） of the two molecules; （4） the emission spectrum of benzil is broader compared to that of PQ due to slower relaxation of the excited state; （5） The CV study shows that PQ and benzil are good electron acceptors and PQ shows a better reduction process than benzil due to an extra ring that provides stability for the reduced species（mono or diradical anions）; （6） TGA shows the higher thermal stability of PQ than benzil attributed to the presence of phenanthrene unit in PQ.
