γ-巴豆酰内酯激发态动力学的共振拉曼光谱和完全活性空间自洽场(CASSCF)计算研究

doi:10.7503/cjcu20150226

摘要/Abstract

摘要：

采用共振拉曼光谱和完全活性空间自洽场(CASSCF)方法研究了γ-巴豆酰内酯的光吸收S₂态的结构动力学和衰变机制. 采用含时密度泛函理论方法结合光谱实验确认了紫外光谱和振动光谱. 获得了涵盖A-带吸收的4个激发波长下的共振拉曼光谱. 用CASSCF计算得到了S_1,min, S_2,min, T_1,min, T_2,min和T_3,min及其相关势能面交叉点的结构与能量. 研究了A-带共振拉曼光谱强度模式与S_2,min和CI(S₂/S₁)交叉点结构的关系. 借助El-Sayed规则分析了各系间窜跃路径的效率, 提出了γ-巴豆酰内酯从S_2,FC弛豫到基态S₀的2条主要路径: 内转换路径和系间窜跃路径.

关键词: γ-巴豆酰内酯, 共振拉曼光谱, 完全活性空间自洽场(CASSCF)计算, 结构动力学, 非绝热动力学, 内转换, 系间窜跃

Abstract:

The structural dynamics and decay mechanisms of γ-crotonolactone in the light-absorbing S₂ excited states were studied by resonance Raman spectroscopy and complete active space self-consistent field(CASSCF) computations. The electronic spectra assignments and the vibrational assignments were done on the basis of the density-functional theory computations and the results of corresponding spectra. The resonance Raman spectra at four excitation wavelength which covered A-band were obtained. CASSCF method was carried out to determine the minimal excitation energies and excited geometries of S_1,min, S_2,min, T_1,min, T_2,min, T_3,min, as well as some conical intersection points. The relation between the structures of excited state $S 2, min$ as well as internal conversion point CI(S₂/S₁) and the intensity mode of resonance Raman spectra was studied. The efficiency of various intersystem crossing is evaluated on the basis of the El-Sayed’s rule, and two major decay channels from S_2,FC to ground state S₀ were proposed. One is the internal conversion channel and the other is the intersystem crossing channel.

Key words: γ-Crotonolactone, Resonance Raman spectrum, Complete active space self-consistent field(CASSCF) computation, Structural dynamics, Non-adiabatic dynamics, Internal conversion, Intersystem crossing

中图分类号:

O641

TrendMD:

欧阳冰, 薛佳丹, 郑旭明. γ-巴豆酰内酯激发态动力学的共振拉曼光谱和完全活性空间自洽场(CASSCF)计算研究. 高等学校化学学报, 2015, 36(10): 1995.

OUYANG Bing, XUE Jiadan, ZHENG Xuming. Excited State Dynamics of γ-Crotonolactone: Resonance Raman Spectroscopy and Complete Active Space Self-consistent Field(CASSCF) Study^†. Chem. J. Chinese Universities, 2015, 36(10): 1995.

图/表 8

Fig.1 UV spectra of γ-crotonolactone in acetonitrile(a) and methanol(b)

Fig.2 Molecular orbitals associated with the electronic transitions

Table 1 Calculated electronic transition energies(ΔE), molecular orbitals and oscillator strengths(f) of γ-crotonolactone

State(C_s)	Orbital	Character	λ/nm(ΔE/eV)		f
State(C_s)	Orbital	Character	Calcd.	Expt.	Calcd.	Expt.^†
S₁(A″)	22→23(0.70)	n_H→ $π L *$	246(5.04)		0
S₂(A')	21→23(0.63)+20→23(-0.29)	π_H-1→ $π L $ +π_H-2→ $π L $	197(6.29)	201	0.2553	0.2784
S₃(A')	20→23(0.64)+21→23(0.28)	π_H-2→ $π L $ +π_H-1→ $π L $	186(6.67)		0.0884

Table 1 Calculated electronic transition energies(ΔE), molecular orbitals and oscillator strengths(f) of γ-crotonolactone

State(C_s)	Orbital	Character	λ/nm(ΔE/eV)		f
State(C_s)	Orbital	Character	Calcd.	Expt.	Calcd.	Expt.^†
S₁(A″)	22→23(0.70)	n_H→ $π L *$	246(5.04)		0
S₂(A')	21→23(0.63)+20→23(-0.29)	π_H-1→ $π L $ +π_H-2→ $π L $	197(6.29)	201	0.2553	0.2784
S₃(A')	20→23(0.64)+21→23(0.28)	π_H-2→ $π L $ +π_H-1→ $π L $	186(6.67)		0.0884

Fig.3 Overall views of the resonance Raman spectra of γ-crotonolactone in acetonitrile(A) and methanol(B)* Labels the solvent subtraction artifacts. a. 204.2 nm; b. 208.8 nm; c. 217.8 nm; d. 228.7 nm.

Fig.4 Enlarged view of the 204.2 nm resonance Raman spectra of γ-crotonolactone in methanol# Marks residual uncertain laser lines.

Table 2 Energies and geometries parameters computed by CASSCF(6,5)/6-31g(d)

State	ΔE/(kJ·mol^-1)(eV)	d_C2—C3/nm	$d C 3 C 4$ /nm	$d C 2 O 6$ /nm	∠ $O 6 C 2 — C 3 C 4$ /(°)
S₀	0	0.1484	0.1335	0.1189	180.0
S_1,FC	510(5.29)
S_1,min(nπ^*)	393(4.07)	0.1355	0.1421	0.1344	-176.0
Δ[S_1,min-S₀]		-0.0129	+0.0086	+0.0155	$4.0$
S_2,FC	753(7.83)
S_2,min(ππ^*)	615(6.38)	0.1387	0.1489	0.1345	-176.2
Δ[S_2,min-S₀]		-0.0097	+0.0154	+0.0156	$3.8$
T_1,min(1)(ππ^*)	309(3.22)	0.1468	0.1495	0.1193	173.4
T_1,min(2)(ππ^*)	380(3.96)	0.1365	0.1.408	0.1341	-170.5
T_2,min(nπ^*)	456(4.73)	0.1332	0.1449	0.1328	-175.2
T_3,min(ππ^*)	498(5.16)	0.1469	0.1321	0.1404	-135.6
CI(S₁/S₀)	556(5.78)	0.1473	0.1319	0.1608	-90.0
CI(S₂/S₁)	690(7.16)	0.1492	0.1428	0.1348	154.5
Δ[CI(S₂/S₁)-S₀]		+0.0008	+0.0093	+0.0159	$25.5$
CI(T₃/T₂)	682(7.06)	0.1487	0.1434	0.1335	152.0
CI(T₂/T₁)(1)	486(4.86)	0.1325	0.1470	0.1331	-176.8
CI(T₂/T₁)(2)	426(4.41)	0.1325	0.1469	0.1331	-176.9
ISC(S₀/T₁)	326(3.39)	0.1501	0.1482	0.1187	158.4
ISC[S₁/T₁(1)]	397(4.03)	0.1358	0.1400	0.1359	-176.3
ISC[S₁/T₁(2)]	389(4.04)	0.1360	0.1413	0.1343	180.0
ISC(S₂/T₃)	644(6.70)	0.1433	0.1500	0.1341	117.2

Table 2 Energies and geometries parameters computed by CASSCF(6,5)/6-31g(d)

State	ΔE/(kJ·mol^-1)(eV)	d_C2—C3/nm	$d C 3 C 4$ /nm	$d C 2 O 6$ /nm	∠ $O 6 C 2 — C 3 C 4$ /(°)
S₀	0	0.1484	0.1335	0.1189	180.0
S_1,FC	510(5.29)
S_1,min(nπ^*)	393(4.07)	0.1355	0.1421	0.1344	-176.0
Δ[S_1,min-S₀]		-0.0129	+0.0086	+0.0155	$4.0$
S_2,FC	753(7.83)
S_2,min(ππ^*)	615(6.38)	0.1387	0.1489	0.1345	-176.2
Δ[S_2,min-S₀]		-0.0097	+0.0154	+0.0156	$3.8$
T_1,min(1)(ππ^*)	309(3.22)	0.1468	0.1495	0.1193	173.4
T_1,min(2)(ππ^*)	380(3.96)	0.1365	0.1.408	0.1341	-170.5
T_2,min(nπ^*)	456(4.73)	0.1332	0.1449	0.1328	-175.2
T_3,min(ππ^*)	498(5.16)	0.1469	0.1321	0.1404	-135.6
CI(S₁/S₀)	556(5.78)	0.1473	0.1319	0.1608	-90.0
CI(S₂/S₁)	690(7.16)	0.1492	0.1428	0.1348	154.5
Δ[CI(S₂/S₁)-S₀]		+0.0008	+0.0093	+0.0159	$25.5$
CI(T₃/T₂)	682(7.06)	0.1487	0.1434	0.1335	152.0
CI(T₂/T₁)(1)	486(4.86)	0.1325	0.1470	0.1331	-176.8
CI(T₂/T₁)(2)	426(4.41)	0.1325	0.1469	0.1331	-176.9
ISC(S₀/T₁)	326(3.39)	0.1501	0.1482	0.1187	158.4
ISC[S₁/T₁(1)]	397(4.03)	0.1358	0.1400	0.1359	-176.3
ISC[S₁/T₁(2)]	389(4.04)	0.1360	0.1413	0.1343	180.0
ISC(S₂/T₃)	644(6.70)	0.1433	0.1500	0.1341	117.2

Fig.5 Optimized geometry structures of the excited states and the conical intersection points ofγ-crotonolactone by CASSCF(6,5)/6-31g(d)

Fig.6 Schematic diagram of the major decay channels of γ-crotonolactone initiated from S2,FC

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