Franklin-Mergarejo R, Alvarez D Ondarse, Tretiak S, Fernandez-Alberti S
Universidad Nacional de Quilmes/CONICET, Roque Saenz Peña 352, B1876BXD Bernal, Argentina.
Theoretical Division, Center for Nonlinear Studies (CNLS), and Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
Sci Rep. 2016 Aug 10;6:31253. doi: 10.1038/srep31253.
Conjugated cycloparaphenylene rings have unique electronic properties being the smallest segments of carbon nanotubes. Their conjugated backbones support delocalized electronic excitations, which dynamics is strongly influenced by cyclic geometry. Here we present a comparative theoretical study of the electronic and vibrational energy relaxation and redistribution in photoexcited cycloparaphenylene carbon nanorings with inserted naphthalene, anthracene, and tetracene units using non-adiabatic excited-state molecular dynamics simulations. Calculated excited state structures reflect modifications of optical selection rules and appearance of low-energy electronic states localized on the acenes due to gradual departure from a perfect circular symmetry. After photoexcitation, an ultrafast electronic energy relaxation to the lowest excited state is observed on the time scale of hundreds of femtoseconds in all molecules studied. Concomitantly, the efficiency of the exciton trapping in the acene raises when moving from naphthalene to anthracene and to tetracene, being negligible in naphthalene, and ~60% and 70% in anthracene and tetracene within the first 500 fs after photoexcitation. Observed photoinduced dynamics is further analyzed in details using induced molecular distortions, delocatization properties of participating electronic states and non-adiabatic coupling strengths. Our results provide a number of insights into design of cyclic molecular systems for electronic and light-harvesting applications.
共轭环对亚苯基具有独特的电子性质，是碳纳米管的最小片段。它们的共轭主链支持离域电子激发，其动力学受到环状几何结构的强烈影响。在这里，我们使用非绝热激发态分子动力学模拟，对插入萘、蒽和并四苯单元的光激发环对亚苯基碳纳米环中的电子和振动能量弛豫及再分布进行了比较理论研究。计算得到的激发态结构反映了光学选择规则的改变以及由于逐渐偏离完美圆对称性而在并苯上出现的低能电子态。光激发后，在所有研究的分子中，在数百飞秒的时间尺度上观察到超快电子能量弛豫到最低激发态。同时，从萘到蒽再到并四苯，激子在并苯中捕获的效率提高，在萘中可忽略不计，在光激发后的前500飞秒内，在蒽和并四苯中分别约为60%和70%。使用诱导分子畸变、参与电子态的离域性质和非绝热耦合强度对观察到的光诱导动力学进行了进一步详细分析。我们的结果为用于电子和光捕获应用的环状分子系统的设计提供了许多见解。
