For decades, the thermal broadening of zero-phonon lines of single organic molecules embedded in amorphous solids was associated with their weak electron-phonon coupling to quasilocal vibrational modes. In this paper we show that the generally accepted perturbative approach for the pure dephasing problem is not applicable to the studied chromophore-doped glass, just as there is no evidence of weak coupling to individual quasilocal modes. Experimental and theoretical analysis of the temperature-dependent fluorescence excitation spectra of single tetra-$tert$-butylterrylene molecules in a polymer matrix of polyisobutylene is used as an example. Analysis of wide-range temperature measurements (9–60 K) with the nonperturbative theory of electron-phonon coupling demonstrates that the observed zero-phonon line broadening is due to the appearance of a wide spectrum of resonant modes induced by the impurity molecules themselves. This spectrum and the associated thermal broadening are obtained in the long-wave approximation for propagating waves using the density of the vibrational states for the host matrix and two quadratic coupling constants describing the interaction between the host and guest molecules. We also test the model considering the resonant modes arising from the host normal modes of a quasilocal character and find it completely incompatible with the experimental results.

中文翻译：

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发色团修饰的振动模式对无序固体中单分子光谱热展宽的关键作用


几十年来，嵌入非晶固体中的单个有机分子的零声子线的热展宽与它们与准局域振动模式的弱电子-声子耦合有关。在本文中，我们表明，普遍接受的纯相移问题的微扰方法不适用于所研究的发色团掺杂玻璃，就像没有证据表明与各个准局域模式存在弱耦合一样。以聚异丁烯聚合物基体中单个四 $tert$ -丁基三萘嵌苯分子的温度依赖性荧光激发光谱的实验和理论分析为例。利用电子声子耦合的非微扰理论对宽范围温度测量（9-60 K）进行分析表明，观察到的零声子线展宽是由于杂质分子本身引起的宽谱谐振模式的出现。该光谱和相关的热展宽是使用主体基质的振动态密度和描述主体和客体分子之间相互作用的两个二次耦合常数在传播波的长波近似中获得的。我们还测试了考虑准局域特征的主法向模式产生的共振模式的模型，发现它与实验结果完全不相容。