Soldatova Alexandra V, Kim Junhwan, Peng Xinzhang, Rosa Angela, Ricciardi Giampaolo, Kenney Malcolm E, Rodgers Michael A J
Center for Photochemical Sciences and Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, USA.
Inorg Chem. 2007 Mar 19;46(6):2080-93. doi: 10.1021/ic061524o. Epub 2007 Feb 15.
The photophysical properties of a group of Ni(II)-centered tetrapyrroles have been investigated by ultrafast transient absorption spectrometry and DFT/TDDFT methods in order to characterize the impacts of alpha-octabutoxy substitution and benzoannulation on the deactivation pathways of the S1(pi,pi*) state. The compounds examined were NiPc, NiNc, NiPc(OBu)8, and NiNc(OBu)8, where Pc = phthalocyanine and Nc = naphthalocyanine. It was found that the S1(pi,pi*) state of NiNc(OBu)8 deactivated within the time resolution of the instrument (200 fs) to a vibrationally hot T1(pi,pi*) state. The quasidegeneracy of the S1(pi,pi*) and 3(dz2,dx2-y2) states allowed for fast intersystem crossing (ISC) to occur. After vibrational relaxation (ca. 2.5 ps), the T1(pi,pi*) converted rapidly (ca. 19 ps lifetime) and reversibly into the 3LMCT(pi,dx2-y2) state. The equilibrium state, so generated, decayed to the ground state with a lifetime of ca. 500 ps. Peripheral substitution of the Pc ring significantly modified the photodeactivation mechanism of the S1(pi,pi*) by inducing substantial changes in the relative energies of the S1(pi,pi*), 3(dpi,dx2-y2), 3(dz2,dx2-y2), T1(pi,pi*), and 1,3LMCT(pi,dx2-y2) excited states. The location of the Gouterman LUMOs and the unoccupied metal level (dx2-y2) with respect to the HOMO is crucial for the actual position of these states. In NiPc, the S1(pi,pi*) state underwent ultrafast (200 fs) ISC into a hot (d,d) state. Vibrational cooling (ca. 20 ps lifetime) resulted in a cold (dz2,dx2-y2) state, which repopulated the ground state with a 300 ps lifetime. In NiPc(OBu)8, the S1(pi,pi*) state deactivated through the 3(dz2,dx2-y2), which in turn converted to the 3LMCT(pi,dx2-y2) state, which finally repopulated the ground state with a lifetime of 640 ps. Insufficient solubility of NiNc in noncoordinating solvents prevented transient absorption data from being obtained for this compound. However, the TDDFT calculations were used to make speculations about the photoproperties.
为了表征α-八丁氧基取代和苯并环化对S1(π,π*)态失活途径的影响，通过超快瞬态吸收光谱和密度泛函理论/含时密度泛函理论（DFT/TDDFT）方法研究了一组以镍(II)为中心的四吡咯的光物理性质。所研究的化合物为NiPc、NiNc、NiPc(OBu)8和NiNc(OBu)8，其中Pc = 酞菁，Nc = 萘酞菁。研究发现，NiNc(OBu)8的S1(π,π*)态在仪器的时间分辨率（200 fs）内失活为振动热的T1(π,π*)态。S1(π,π*)态和3(dz2,dx2 - y2)态的准简并性使得快速系间窜越（ISC）得以发生。经过振动弛豫（约2.5 ps）后，T1(π,π*)态迅速（约19 ps寿命）且可逆地转变为3LMCT(π,dx2 - y2)态。如此产生的平衡态以约500 ps的寿命衰减至基态。Pc环的外围取代通过引起S1(π,π*)、3(dπ,dx2 - y2)、3(dz2,dx2 - y2)、T1(π,π*)和1,3LMCT(π,dx2 - y2)激发态相对能量的显著变化，显著改变了S1(π,π*)的光致失活机制。Gouterman最低未占分子轨道（LUMO）和未占据金属能级（dx2 - y2）相对于最高已占分子轨道（HOMO）的位置对于这些态的实际位置至关重要。在NiPc中，S1(π,π*)态经历超快（200 fs）ISC进入热的(d,d)态。振动冷却（约20 ps寿命）产生冷的(dz2,dx2 - y2)态，其以300 ps的寿命重新回到基态。在NiPc(OBu)8中，S1(π,π*)态通过3(dz2,dx2 - y2)失活，3(dz2,dx2 - y2)又转变为3LMCT(π,dx2 - y2)态，最终以640 ps的寿命重新回到基态。NiNc在非配位溶剂中的溶解度不足，无法获得该化合物的瞬态吸收数据。然而，TDDFT计算被用于推测其光性质。
