Karlsson Joshua K G, Atahan Alparslan, Harriman Anthony, Tkachenko Nikolai V, Ward Andrew D, Schaberle Fabio A, Serpa Carlos, Arnaut Luis G
Molecular Photonics Laboratory, School of Natural and Environmental Sciences, Newcastle University, Bedson Building, Newcastle upon Tyne NE1 7RU, U.K.
Faculty of Engineering and Natural Sciences, Tampere University, Koereakoulunkatu 7, FIN-33720 Tampere, Finland.
J Phys Chem A. 2021 Feb 11;125(5):1184-1197. doi: 10.1021/acs.jpca.0c09961. Epub 2021 Feb 2.
A covalently linked bichromophore, embracing 6,13-bis(triisopropylsilylethinyl)pentacene (TIPS-pentacene) terminals bridged by a rigid fluorene spacer, generates a relatively high yield (i.e., 65 ± 6%) of the spin-correlated, triplet biexciton upon illumination in toluene. Under the same conditions, the extent of fluorescence quenching relative to the parent TIPS-pentacene approaches 97% and is insensitive to temperature. The biexciton, having overall singlet spin multiplicity, undergoes internal conversion in competition to spin decorrelation. These latter processes occur on the relatively slow time scale of a hundred or so nanoseconds, possibly reflecting the restricted level of electronic communication between the terminals. Spin decorrelation leads to evolution of an independent triplet pair with an overall quantum yield of 0.50 ± 0.06 and a lifetime of 8 ± 2 μs in deaerated toluene. Photoacoustic calorimetry (PAC) indicates three separate enthalpy changes: a very fast step associated with intramolecular singlet exciton fission to form the correlated triplet biexciton, a fast step essentially reflecting spin decorrelation, and a slow step associated with relaxation of the independent triplet pair. Analysis of the PAC data, in conjunction with the transient absorption results, establishes excitation energies for both spin-correlated and independent triplet pairs. Polar solvent enhances both fluorescence quenching and triplet formation at the expense of radiationless decay while temperature effects have been recorded for all important intermediate species.
一种共价连接的双色团，包含由刚性芴间隔基桥接的6,13-双（三异丙基甲硅烷基乙炔基）并五苯（TIPS-并五苯）末端，在甲苯中光照时产生相对较高产率（即65±6%）的自旋相关三重态双激子。在相同条件下，相对于母体TIPS-并五苯的荧光猝灭程度接近97%，且对温度不敏感。具有整体单重态自旋多重性的双激子在与自旋去相关竞争中发生内转换。后一过程发生在大约一百纳秒的相对较慢时间尺度上，这可能反映了末端之间电子通信的受限水平。自旋去相关导致在脱氧甲苯中形成一个独立的三重态对，其总量子产率为0.50±0.06，寿命为8±2微秒。光声量热法（PAC）表明有三个独立的焓变：一个与分子内单重态激子裂变形成相关三重态双激子相关的非常快的步骤，一个基本上反映自旋去相关的快速步骤，以及一个与独立三重态对弛豫相关的缓慢步骤。结合瞬态吸收结果对PAC数据的分析，确定了自旋相关和独立三重态对的激发能。极性溶剂以无辐射衰变的减少为代价增强了荧光猝灭和三重态形成，同时记录了所有重要中间物种的温度效应。
