2-硫代嘧啶酮和2-硫代吡啶酮在B-吸收带中的动态结构

Dynamic Structures of 2-Thiopyrimidone and 2-Thiopyridone in B-Band Absorptions

采用共振拉曼光谱学结合量子化学计算研究了2-硫代嘧啶酮(2TPM)和2-硫代吡啶酮(2TP)在B-带吸收时的动态结构.在气相时,2-巯基嘧啶(2MPM,硫醇式)比2TPM(硫代酮式)更稳定,能量差约为15.1kJ·mol-1,而在水和乙腈溶液中,2TPM比2MPM更稳定,能量差分别为29.3和28.0kJ·mol-1.气相及基电子态时,由B3LYP/6-311++G(d,p)计算水平获得的2TPM和2MPM之间发生质子转移异构化反应的过渡态能垒约为130kJ·mol-1.2TPM三个吸收带分别被指认为πH→π*L,ππH→π*L+1和πH-1→π*L跃迁.基于对2TPM在固体和溶液相傅里叶变换-拉曼(FT-Raman)和傅里叶变换-红外(FT-IR)光谱测量,以及B3LYP/6-311++G(d,p)计算,开展了2TPM在水和乙腈溶液中的B-带共振拉曼光谱的振动指认,由此获得了2TPM的动态结构,并与2TP的动态结构进行了比较.2TPM和2TP动态结构的差异反映了ππ*/πσ*锥形交叉点结构的差异,因此,可被用于洞察光诱导的氢原子脱离-复合机制.

The dynamic structures of 2-thiopyrimidone （2TPM） and 2-thiopyridone （2TP） in B-band absorptions were studied using the resonance Raman spectroscopy combined with quantum chemical calculations. In gas phase, 2-thiopyrimidine （2MPM, the thiol form） was more stable than 2TPM （the thione form） by -15.1 kJ. mo^（-1）, whereas in water and acetonitrile 2TPM was more stable than 2MPM by 29.3 and 28.0 kJ ·mol^（-1）, respectively. The transition barrier for the ground state proton transfer tautomerization reaction between 2TPM and 2MPM was -130 kJ. mol^（-1） in gas phase on the basis of the B3LYP/6-311 ＋＋ G（d,p） level of theory calculations. The three absorption bands of 2-thiopyrimidone were respectively assigned as πH→π（^＊,L）,πH→π（^＊,L＋1）, andπ（H-1）→π（^＊,L）; transitions. The vibrational assignments were carried out for the B-band resonance Raman spectra of 2TPM in water and acetonitrile solvents on the basis of the measurements from the Fourier transform （FT）-Raman and Fourier transform-infrared （FT-IR） spectra of 2TPM in solid and/or in solution phases and B3LYP/6-311 ＋＋G（d,p） computations. The dynamic structures of 2TPM and 2TP were obtained by analysis of the resonance Raman intensity pattern. The differences in the dynamic structures of 2TPM and 2TP reflected differences in the structures of their ππ＊/πσ conical intersection points, and therefore could be used to provide insight into the photoinduced hydrogen-atom detachment-attachment mechanism.