Nonplanar heme deformations and excited state displacements in nickel porphyrins detected by Raman spectroscopy at Soret excitation
Nonplanar heme deformations and excited state displacements in nickel porphyrins detected by Raman spectroscopy at Soret excitation
复制标题
DOI：
10.1021/jp052986a
复制
发表时间：
2005-11-24
影响因子：
2.9
通讯作者：
Schweitzer-Stenner, R
中科院分区：
文献类型：
--
作者：
Huang, Q;Medforth, CJ;Schweitzer-Stenner, R
我们将镍卟啉的面外模式的拉曼强度与特定对称性的非平面变形，即用无扰动D-4h点群的不可约表示表示的静态法向坐标变形（SNCDs）联系起来。选择模型卟啉Ni（II）八乙基四苯基卟啉（NiOETPP）、Ni（II）四（异丙基）卟啉（NiT(Pr-i)P）、Ni（II）四（叔丁基）卟啉（NiT('Bu)P）和Ni（II）中四苯基卟啉（NiTPP）是因为它们表现出不同对称性的显着面外变形。在b波段激发下，面外模式的拉曼散射主要通过frank - condon机制被激活。光谱中的一些面外模态特征波段被确定为面外变形类型和大小的可靠预测因子。伽玛(10)-伽玛（13）波段是卟啉的皱折（B-1u）变形的指标，这一点得到了NiTPP、NiT(iPr)P和NiT('Bu)P数据的证实，其中拉曼强度随着皱折变形的大小而增加。伽马(15)-伽马（17）波段是鞍态（B-2u）变形的指标，如NiOETPP的数据所示，它是高度鞍态的。通过比较这些突出的拉曼波段的相对强度，我们使用自一致的分析估计了振动耦合参数，并表明它们再现了各自的b波段吸收谱。我们还确定了沿最低波数法坐标的变形是面外模式拉曼活动的主要原因。我们的结果表明，一些法向坐标（gamma（10）和gamma(13)）可以用作定量探测在介观位置具有烷基取代基的金属卟啉的非平面变形的工具。面外变形还增加了一些低频面内拉曼模的振动耦合强度，即nu(7)和nu(8)。一般来说，拉曼数据表明激发态比基态更非平面。褶边卟啉整体上较大的振动耦合使得与b态跃迁相关的振动侧带具有较大的偶极子强度，因此B-nu带的相对吸收率可以作为一种方便的工具来探测卟啉大环的非平面性。
We have correlated the Raman intensities of out-of-plane modes of nickel porphyrins with the nonplanar deformations of specific symmetries, i.e., static normal coordinate deformations (SNCDs) expressed in terms of irreducible representations of the unperturbed D-4h point group. The model porphyrins Ni(II) octaethyltetra-phenylporphyrin (NiOETPP), Ni(II) tetra(isopropyl)porphyrin (NiT(Pr-i)P), Ni(II) tetra(tert-butyl)porphyrin (NiT('Bu)P), and Ni(II) meso-tetraphenylporphyrin (NiTPP) were chosen because they exhibit significant out-of-plane deformations of different symmetries. At B-band excitation, the Raman scattering of out-of-plane modes becomes activated mostly via the Franck-Condon mechanism. Some characteristic bands from out-of-plane modes in the spectra were identified as reliable predictors of the type and magnitude of out-of-plane deformation. The gamma(10)-gamma(13) bands are indicators of ruffling (B-1u) deformations for porphyrins, as confirmed by data for NiTPP, NiT(iPr)P, and NiT('Bu)P, where the Raman intensity increases with the magnitude of the ruffling deformation. The gamma(15)-gamma(17) bands are indicators of saddling (B-2u) deformations, as shown by data for NiOETPP, which is highly saddled. By comparing the relative intensities of these prominent Raman bands we estimated the vibronic coupling parameters using a self-consistent analysis, and showed that they reproduce the respective B-band absorption profiles. We also identified the deformations along the lowest wavenumber normal coordinates as the predominant reason for the Raman activity of out-of-plane modes. Our results suggest that some of the normal coordinates (gamma(10) and gamma(13)) may be used as tools to quantitatively probe the nonplanar deformations of metalloporphyrins with alkyl substituents at the meso-positions. Out-of-plane deformations also increase the vibronic coupling strength of some low frequency in-plane Raman modes, namely, nu(7) and nu(8). Generally, the Raman data suggest that the excited B-state is substantially more nonplanar than the ground state. The overall larger vibronic coupling of ruffled porphyrins yields substantially larger dipole strengths for the vibronic sidebands associated with the B-state transition, so that the relative absorptivity of the B-nu band can be used as a convenient tool to probe the nonplanarity of the porphyrin macrocycle.