Yi John T, Alvarez-Valtierra Leonardo, Pratt David W
Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
J Chem Phys. 2006 Jun 28;124(24):244302. doi: 10.1063/1.2206782.
Rotationally resolved fluorescence excitation spectra of the S1 <-- S0 origin bands and higher vibronic bands of fluorene (FLU), carbazole (CAR), and dibenzofuran (DBF) have been observed and assigned. Analyses of these data show that replacement of the CH2 group in FLU with a NH group in CAR and an O atom in DBF produces only localized changes in structure, in the ground state. But the three molecules exhibit different changes in geometry when they are excited by light. The S1 states of the three molecules also are electronically very different. The S1 <-- S0 transition moments of CAR and DBF are parallel to the C2 symmetry axis whereas the corresponding transition moment in FLU is perpendicular to this axis. Herzberg-Teller coupling involving the S2 state also has been observed in the spectra of higher vibronic bands of CAR and DBF. Possible reasons for these behaviors are discussed.
已观测并归属了芴（FLU）、咔唑（CAR）和二苯并呋喃（DBF）的S1 ← S0起始带及更高振动电子带的转动分辨荧光激发光谱。对这些数据的分析表明，在基态下，用咔唑中的NH基团和二苯并呋喃中的O原子取代芴中的CH2基团仅产生结构上的局部变化。但当这三种分子被光激发时，它们在几何结构上表现出不同的变化。这三种分子的S1态在电子结构上也有很大差异。咔唑和二苯并呋喃的S1 ← S0跃迁矩与C2对称轴平行，而芴中的相应跃迁矩垂直于该轴。在咔唑和二苯并呋喃的更高振动电子带光谱中也观测到了涉及S2态的赫兹伯格-泰勒耦合。讨论了这些行为的可能原因。
