Nanosecond transient absorption spectroscopy was used to study the photochemical ring-opening reaction for a 6-nitroindolinospiropyran (SP1) in solution and in nanocrystalline (NC) suspension at 298 K. We measured the kinetics in argon purged and air saturated acetonitrile and found that the presence of oxygen affected two out of the three components of the kinetic decay at 440 nm. These are assigned to the triplet excited states of the Z- and E-merocyanines (³Z-MC* and ³E-MC*). In contrast, a long-lived growth component at 550 nm and the decay of a band centered at 590 nm showed no dependence on oxygen and are assigned, respectively, to the ground state Z- and E-merocyanines (Z-MC₀ and E-MC₀). Laser flash photolysis studies performed in NC suspensions initially showed a very broad, featureless absorption spectrum that decayed uniformly for ca. 70 ns before revealing a more defined spectrum that persisted for greater than 4 ms and is consistent with a mixture of the more stable Z- and E-MC₀ structures. We performed quantum mechanical calculations on the interconversion of E- and Z-MCs on the S₀ and S₁ potential energy surfaces. The computed UV-vis spectra for a scan along the Z → E interconversion reaction coordinate show substantial absorptivity from 300–600 nm, which suggests that the broad, featureless transient absorption spectrum results from the contribution of the transition structure and other high-energy species during the Z to E isomerization.

中文翻译：

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在单激发条件下溶液和纳米晶悬浮液中的6-硝基吲哚螺并吡喃的纳秒激光闪光光解

纳秒瞬态吸收光谱法用于研究溶液中和298 K纳米晶（NC）悬浮液中6-硝基吲哚螺并吡喃（SP1）的光化学开环反应。我们测量了吹扫氩气和空气饱和乙腈的动力学，发现氧的存在影响了440 nm动力学衰减的三个成分中的两个。这些被分配给Z-和E-花青素的三重态激发态（³ Z -MC *和³ E -MC *）。相反，在550 nm处有长寿命的生长成分和在590 nm处的能带衰减显示不依赖于氧，并分别分配给基态Z-和E-花青素（Z -MC ₀和E -MC ₀）。最初在NC悬浮液中进行的激光闪光光解研究显示，非常宽广，无特征的吸收光谱在大约20nm内均匀衰减。前露出了更定义频谱持续了大于4毫秒，并且与更稳定的混合物一致70纳秒ž -和Ë -MC ₀结构。我们上的相互进行量子力学计算ë -和ž -MC上的S小号₀和小号_1个势能面。沿着Z→E互转换反应坐标进行扫描的计算得出的UV-vis光谱显示出300-600 nm的吸收率，这表明过渡结构和其他高能物质的贡献导致了宽广，无特征的瞬态吸收光谱在Z到E异构化过程中。