Hoffelt Laura M, Springer Mitchell G, Drucker Stephen
Department of Chemistry, University of Wisconsin Eau Claire, Eau Claire, WI 54702-4004, USA.
J Chem Phys. 2008 Mar 14;128(10):104312. doi: 10.1063/1.2834922.
The phosphorescence excitation (PE) spectrum of 4H-pyran-4-one (4PN) vapor at 40-50 degrees C was recorded near 366 nm. The most intense vibronic feature in this region of the spectrum is the T(1)(n,pi*)<--S(0) origin band. The value of nu(0) for the 0(0)(0) transition was determined to be 27 291.5 cm(-1) by comparing the observed spectrum to a simulation in the T(1)<--S(0) origin-band region. Attached to the origin band in the PE spectrum are several Deltav=0 sequence bands involving low-frequency ring modes. From the positions of these bands, together with the known ground-state combination differences, fundamental frequencies for nu(18') (ring bending), nu(13') (ring twisting), and nu(10') (in-plane ring deformation) in the T(1)(n,pi*) excited state were determined to be 126, 269, and 288 cm(-1), respectively. These values represent drops of 15%, 32%, and 43%, compared to the respective fundamental frequencies in the S(0) state. The changes in these ring frequencies indicate that the effects of T(1)(n,pi*)<--S(0) excitation extend beyond the nominal carbonyl chromophore and involve the conjugated ring atoms as well. The delocalization may be more extensive for T(1)(n,pi*) than for S(1)(n,pi*) excitation.
在40 - 50摄氏度下记录了4H - 吡喃 - 4 - 酮（4PN）蒸气在366 nm附近的磷光激发（PE）光谱。该光谱区域中最强的振动特征是T(1)(n,π*) ← S(0) 起始带。通过将观察到的光谱与T(1) ← S(0) 起始带区域的模拟进行比较，确定0(0)(0)跃迁的ν(0)值为27291.5 cm⁻¹。在PE光谱中，起始带附近有几个涉及低频环模式的Δv = 0序列带。根据这些带的位置，结合已知的基态组合差异，确定T(1)(n,π*)激发态中ν(18')（环弯曲）、ν(13')（环扭转）和ν(10')（面内环变形）的基频分别为126、269和288 cm⁻¹。与S(0)态中的相应基频相比，这些值分别下降了15%、32%和43%。这些环频率的变化表明，T(1)(n,π*) ← S(0)激发的影响超出了名义上的羰基发色团，还涉及共轭环原子。T(1)(n,π*)的离域可能比S(1)(n,π*)激发更广泛。
