How Delocalized Is N,N,N‘,N‘-Tetraphenylphenylenediamine Radical Cation? An Experimental and Theoretical Study on the Electronic and Molecular Structure

The electronic and molecular structure of N,N,N‘,N‘-tetraphenylphenylenediamine radical cation
1+ is in focus of this study. Resonance Raman experiments showed that at least eight vibrational modes
are strongly coupled to the optical charge resonance band which is seen in the NIR. With the help of a
DFT-based vibrational analysis, these eight modes were assigned to symmetric vibrations. The contribution
of these symmetric modes to the total vibrational reorganization energy is dominant. These findings are in
agreement with the conclusions from a simple two-state two-mode Marcus−Hush analysis which yields a
tiny electron-transfer barrier. The excellent agreement of the X-ray crystal structure analysis and the DFT
computed molecular structure of 1+ on one hand as well as the solvent and solid-state IR spectra and the
DFT-calculated IR active vibrations on the other hand prove 1+ adopts a symmetrical delocalized Robin−Day class III structure both in the solid state and in solution.

本研究聚焦于N,N,N'，N'-四苯基苯基二胺自由基阳离子1+的电子和分子结构。共振拉曼实验表明，至少有八个振动模式与近红外区域的电荷共振带强烈耦合。借助基于密度泛函理论的振动分析，这八个模式被归因于对称振动。这些对称模式对总振动重排能量的贡献占据主导地位。这些发现与简单二态双模式Marcus-Hush分析的结论相一致，该分析得出微小的电子转移势垒。一方面，X射线晶体结构分析与DFT计算的1+分子结构以及另一方面溶剂和固态红外光谱以及DFT计算的活性红外振动之间的出色一致证明了1+在固态和溶液中均采用对称的共轭Robin-Day III类结构。