Balmer Franziska A, Ottiger Philipp, Leutwyler Samuel
Department of Chemistry and Biochemistry, University of Bern , Freiestrasse 3, CH-3012 Bern, Switzerland.
J Phys Chem A. 2015 Oct 22;119(42):10462-74. doi: 10.1021/acs.jpca.5b08225. Epub 2015 Oct 12.
The S0 ↔ S1 spectra of the mild charge-transfer (CT) complexes perylene·tetrachloroethene (P·4ClE) and perylene·(tetrachloroethene)2 (P·(4ClE)2) are investigated by two-color resonant two-photon ionization (2C-R2PI) and dispersed fluorescence spectroscopy in supersonic jets. The S0 → S1 vibrationless transitions of P·4ClE and P·(4ClE)2 are shifted by δν = -451 and -858 cm(-1) relative to perylene, translating to excited-state dissociation energy increases of 5.4 and 10.3 kJ/mol, respectively. The red shift is ∼30% larger than that of perylene·trans-1,2-dichloroethene; therefore, the increase in chlorination increases the excited-state stabilization and CT character of the interaction, but the electronic excitation remains largely confined to the perylene moiety. The 2C-R2PI and fluorescence spectra of P·4ClE exhibit strong progressions in the perylene intramolecular twist (1au) vibration (42 cm(-1) in S0 and 55 cm(-1) in S1), signaling that perylene deforms along its twist coordinate upon electronic excitation. The intermolecular stretching (Tz) and internal rotation (Rc) vibrations are weak; therefore, the P·4ClE intermolecular potential energy surface (IPES) changes little during the S0 ↔ S1 transition. The minimum-energy structures and inter- and intramolecular vibrational frequencies of P·4ClE and P·(4ClE)2 are calculated with the dispersion-corrected density functional theory (DFT) methods B97-D3, ωB97X-D, M06, and M06-2X and the spin-consistent-scaled (SCS) variant of the approximate second-order coupled-cluster method, SCS-CC2. All methods predict the global minima to be π-stacked centered coplanar structures with the long axis of tetrachloroethene rotated by τ ≈ 60° relative to the perylene long axis. The calculated binding energies are in the range of -D0 = 28-35 kJ/mol. A second minimum is predicted with τ ≈ 25°, with ∼1 kJ/mol smaller binding energy. Although both monomers are achiral, both the P·4ClE and P·(4ClE)2 complexes are chiral. The best agreement for adiabatic excitation energies and vibrational frequencies is observed for the ωB97X-D and M06-2X DFT methods.
通过双色共振双光子电离（2C-R2PI）和超声速射流中的色散荧光光谱，研究了轻度电荷转移（CT）配合物苝·四氯乙烯（P·4ClE）和苝·（四氯乙烯）2（P·(4ClE)2）的S0 ↔ S1光谱。相对于苝，P·4ClE和P·(4ClE)2的S0 → S1无振动跃迁发生了δν = -451和-858 cm(-1)的位移，分别对应激发态势能增加5.4和10.3 kJ/mol。这种红移比苝·反式-1,2-二氯乙烯的红移大约30%；因此，氯化程度的增加增强了激发态稳定性和相互作用的CT特性，但电子激发仍主要局限于苝部分。P·4ClE的2C-R2PI和荧光光谱在苝分子内扭转（1au）振动（S0中为42 cm(-1)，S1中为55 cm(-1)）上表现出强烈的进展，表明苝在电子激发时沿其扭转坐标发生变形。分子间拉伸（Tz）和内旋转（Rc）振动较弱；因此，P·4ClE分子间势能面（IPES）在S0 ↔ S1跃迁过程中变化很小。使用色散校正密度泛函理论（DFT）方法B97-D3、ωB97X-D、M06和M06-2X以及近似二阶耦合簇方法的自旋一致缩放（SCS）变体SCS-CC2，计算了P·4ClE和P·(4ClE)2的最低能量结构以及分子间和分子内振动频率。所有方法都预测全局最小值是π堆积的中心共面结构，四氯乙烯的长轴相对于苝的长轴旋转了τ ≈ 60°。计算得到的结合能在-D0 = 28 - 35 kJ/mol范围内。预测还有一个最小值，τ ≈ 25°，结合能小约1 kJ/mol。尽管两种单体都是非手性的，但P·4ClE和P·(4ClE)2配合物都是手性的。对于绝热激发能和振动频率，ωB97X-D和M06-2X DFT方法的吻合度最佳。
