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One-Dimensionally Conjugated Carbocyanine Dyes Isolated under Cold Gas-Phase Conditions: Electronic Spectra and Photochemistry
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2022-10-26 , DOI: 10.1021/acs.jpca.2c05111 Satoru Muramatsu 1 , Takayuki Tokizane 1 , Yoshiya Inokuchi 1
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2022-10-26 , DOI: 10.1021/acs.jpca.2c05111 Satoru Muramatsu 1 , Takayuki Tokizane 1 , Yoshiya Inokuchi 1
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One-dimensionally conjugated carbocyanine dyes are of significant research interest, particularly for their electronic photoexcitation, owing to a wide variety of characteristics, including a good analogy to “free electrons in a one-dimensional box” model and trans–cis photoisomerization along the conjugated chain. Despite these important aspects, their electronic spectra remain ambiguous in terms of their assignment owing to the significant effects of their surrounding environment. In this study, we present the electronic spectra of two cyanine dyes, 1,1′-diethyl-2,2′-carbocyanine (pinacyanol, 1) and 1,1′-diethyl-4,4′-carbocyanine (cryptocyanine, 2), measured under cold (∼10 K) gas-phase conditions, to determine the intrinsic electronic transition energy and provide clear assignments for the spectra. The obtained visible photodissociation spectra demonstrate (1) spectral shifts in response to both solvent and temperature, (2) the contribution from the vibrational excitation in the excited state (Franck–Condon (FC) activity), and (3) the coexistence of conformers caused by the orientation of the side ethyl groups. These factors affect the electronic transition energy up to ∼1000 cm–1 in total for both 1 and 2, which corresponds to an effective length of 0.5 Å in terms of the “one-dimensional box” model. Furthermore, a difference was observed in the effective bandwidth of the spectra between 1 and 2 based on a comparison with the simulated FC patterns around the origin band; the bandwidth was substantially larger for 2 than that of 1, implying the shorter lifetime of 2 in the photoexcited S1 state. With the aid of density functional theory (DFT) calculations of the relaxed potential energy curves, we partly ascribed this to the fast trans–cis photoisomerization via C═C bond twisting on the S1 surface, followed by S1–S0 internal conversion.
中文翻译：
在冷气相条件下分离的一维共轭羰花青染料：电子光谱和光化学
一维共轭羰花青染料具有重要的研究意义，特别是它们的电子光激发，由于其广泛的特性，包括与“一维盒中的自由电子”模型的良好类比和沿共轭的反式-顺式光异构化链。尽管有这些重要方面，但由于周围环境的显着影响，它们的电子光谱在分配方面仍然不明确。在这项研究中，我们展示了两种花青染料 1,1'-diethyl-2,2'-carbocyanine（pinacyanol，1）和 1,1'-diethyl-4,4'-carbocyanine（隐花青，2），在冷（~10 K）气相条件下测量，以确定固有的电子跃迁能量并为光谱提供清晰的分配。获得的可见光解离光谱表明 (1) 响应溶剂和温度的光谱偏移，(2) 激发态振动激发的贡献（Franck–Condon (FC) 活性），以及 (3) 构象异构体的共存由侧乙基的取向引起。这些因素对1和2的电子跃迁能量的影响总计高达 ∼1000 cm –1，就“一维盒”模型而言，这对应于 0.5 Å 的有效长度。此外，观察到光谱的有效带宽存在差异1和2基于与原带周围的模拟 FC 模式的比较；2的带宽明显大于1的带宽，这意味着2在光激发 S 1状态下的寿命较短。借助于松弛势能曲线的密度泛函理论 (DFT) 计算，我们部分将此归因于通过 S 1表面上的 C═C 键扭曲进行的快速反式-顺式光异构化，然后是 S 1 -S 0内部转换.
更新日期：2022-10-26
中文翻译：
在冷气相条件下分离的一维共轭羰花青染料：电子光谱和光化学
一维共轭羰花青染料具有重要的研究意义，特别是它们的电子光激发，由于其广泛的特性，包括与“一维盒中的自由电子”模型的良好类比和沿共轭的反式-顺式光异构化链。尽管有这些重要方面，但由于周围环境的显着影响，它们的电子光谱在分配方面仍然不明确。在这项研究中，我们展示了两种花青染料 1,1'-diethyl-2,2'-carbocyanine（pinacyanol，1）和 1,1'-diethyl-4,4'-carbocyanine（隐花青，2），在冷（~10 K）气相条件下测量，以确定固有的电子跃迁能量并为光谱提供清晰的分配。获得的可见光解离光谱表明 (1) 响应溶剂和温度的光谱偏移，(2) 激发态振动激发的贡献（Franck–Condon (FC) 活性），以及 (3) 构象异构体的共存由侧乙基的取向引起。这些因素对1和2的电子跃迁能量的影响总计高达 ∼1000 cm –1，就“一维盒”模型而言，这对应于 0.5 Å 的有效长度。此外，观察到光谱的有效带宽存在差异1和2基于与原带周围的模拟 FC 模式的比较；2的带宽明显大于1的带宽，这意味着2在光激发 S 1状态下的寿命较短。借助于松弛势能曲线的密度泛函理论 (DFT) 计算，我们部分将此归因于通过 S 1表面上的 C═C 键扭曲进行的快速反式-顺式光异构化，然后是 S 1 -S 0内部转换.
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