We report the electrogenerated chemiluminescence (ECL) of 2,2'-bis(10-phenylanthracen-9-yl)-9,9'-spirobifluorene (spiro-FPA), a dichromophoric molecule composed of two phenylanthracenes linked by a spirobifluorene moiety (PA-X-PA). The results are compared to those for 9,10-diphenylanthracene (DPA), a related molecule with a single chromophore. Cyclic voltammetry (CV) of spiro-FPA shows two reversible, closely spaced, one-electron transfers on both reduction and oxidation, occurring at E(o)(1,red) = -2.02, E(o)(2,red) = -2.07 V vs SCE and E(o)(1,ox) = 1.14, E(o)(2,ox) = 1.20 V vs SCE. The potentials for each pair are close enough to appear as a single peak in CV, indicating that the spirobifluorene moiety interrupts conjugation between the redox centers. The potentials observed are similar to those of DPA, which shows E(o)(red) = -2.06 V vs SCE and E(o)(ox) = 1.15 V vs SCE. The absorbance spectrum of spiro-FPA shows lambda(max,abs) = 377 nm, with 377 = 25,700 M(-1) s(-1), while DPA exhibited lambda(max,abs) = 374 nm, with 374 = 13,800 M(-1) s(-1), demonstrating that spiro-FPA has twice the available chromophores as DPA. Photoluminescence (PL) data for spiro-FPA shows lambda(max,PL) = 434 nm, with Phi(PL) = 0.74, while DPA fluoresces at 420 nm with Phi(PL) = 0.91; thus, there is greater solvent or structural relaxation in the spiro-FPA excited state, which may account for the greater internal conversion. Unlike DPA, the ECL spectrum of spiro-FPA exhibits long-wavelength emission not observed in the PL. We attribute this emission to excimers formed during annihilation ECL. Steric hindrance prevents DPA from forming excimers, even in ECL, but spiro-FPA annihilation can occur between pairs of di-ions (PA(*-)-X-PA(*-) and PA(*+)-X-PA(*+)), which are electrostatically more strongly attracted to one another than the mono-ions. This greater electrostatic attraction may be sufficient to overcome the steric hindrance to excimer formation. Lowering the electrolyte concentration decreases the electrostatic shielding of the ions from one another; thus, the increase in longer wavelength ECL accompanying a decrease in electrolyte concentration supports the role of the di-ions in excimer formation. Additionally, simulations show, consistent with experiment, a more rapid decrease in excimer concentration than in excited monomer concentration as a function of time after each potential pulse. This is probably due to the greater number of scavenging reactions available for di-ions. The simulations are confirmed experimentally when lower potential pulsing frequencies yield lower relative excimer emission. Since an excited state created by one-electron transfer between two di-ions should be rapidly quenched via electron transfer by the other PA moiety, the existence of excimers suggests the possibility of simultaneous, two-electron transfer to generate the excimer.

中文翻译：

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Spirobifluorene-Linked Bisanthracene 的电生化学发光：一种可能的同时，双电子转移

我们报告了 2,2'-双(10-苯基蒽-9-基)-9,9'-螺二芴 (spiro-FPA) 的电致化学发光 (ECL)，这是一种二发色分子，由两个由螺二芴部分连接的苯基蒽组成PA-X-PA）。将结果与 9,10-二苯基蒽 (DPA)（一种具有单个发色团的相关分子）的结果进行比较。spiro-FPA 的循环伏安法 (CV) 显示在还原和氧化过程中发生两个可逆的、紧密间隔的单电子转移，发生在 E(o)(1,red) = -2.02, E(o)(2,red) = -2.07 V vs SCE 和 E(o)(1,ox) = 1.14, E(o)(2,ox) = 1.20 V vs SCE。每对的电位足够接近以在 CV 中显示为单个峰，表明螺二芴部分中断了氧化还原中心之间的共轭。观察到的电位与 DPA 的电位相似，显示 E(o)(red) = -2。06 V vs SCE 和 E(o)(ox) = 1.15 V vs SCE。spiro-FPA 的吸收光谱显示 lambda(max,abs) = 377 nm，377 = 25,700 M(-1) s(-1)，而 DPA 显示 lambda(max,abs) = 374 nm，374 = 13,800 M(-1) s(-1)，表明螺-FPA 的可用发色团是 DPA 的两倍。spiro-FPA 的光致发光 (PL) 数据显示 lambda(max,PL) = 434 nm，Phi(PL) = 0.74，而 DPA 在 420 nm 处发出荧光，Phi(PL) = 0.91；因此，spiro-FPA 激发态存在更大的溶剂或结构弛豫，这可能是更大的内部转化。与 DPA 不同，spiro-FPA 的 ECL 光谱表现出在 PL 中未观察到的长波长发射。我们将这种发射归因于湮灭 ECL 期间形成的准分子。空间位阻阻止 DPA 形成准分子，即使在 ECL 中，但螺-FPA 湮灭可能发生在双离子对（PA(*-)-X-PA(*-) 和 PA(*+)-X-PA(*+)）之间，它们在静电上更强烈地吸引到与单离子不同。这种更大的静电吸引力可能足以克服准分子形成的空间位阻。降低电解质浓度会降低离子之间的静电屏蔽；因此，随着电解质浓度降低，更长波长 ECL 的增加支持了双离子在准分子形成中的作用。此外，模拟表明，与实验一致，在每个潜在脉冲后，作为时间函数的受激单体浓度比激发单体浓度下降得更快。这可能是由于可用于二离子的清除反应数量较多。当较低的潜在脉冲频率产生较低的相对准分子发射时，模拟得到了实验证实。由于两个双离子之间的单电子转移产生的激发态应通过另一个 PA 部分的电子转移迅速淬灭，因此准分子的存在表明同时进行双电子转移以产生准分子的可能性。