Rogers Joy E, Slagle Jonathan E, Krein Douglas M, Burke Aaron R, Hall Benjamin C, Fratini Albert, McLean Daniel G, Fleitz Paul A, Cooper Thomas M, Drobizhev Mikhail, Makarov Nikolay S, Rebane Aleksander, Kim Kye-Young, Farley Richard, Schanze Kirk S
Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, OH 45433, USA.
Inorg Chem. 2007 Aug 6;46(16):6483-94. doi: 10.1021/ic700549n. Epub 2007 Jul 10.
To explore the photophysics of platinum acetylide chromophores with strong two-photon absorption cross-sections, we have investigated the synthesis and spectroscopic characterization of a series of platinum acetylide complexes that feature highly pi-conjugated ligands substituted with pi-donor or -acceptor moieties. The molecules (numbered 1-4) considered in the present work are analogs of bis(phenylethynyl)bis(tributylphosphine)platinum(II) complexes. Molecule 1 carries two alkynyl-benzothiazolylfluorene ligands, and molecule 2 has two alkynyl-diphenylaminofluorene ligands bound to the central platinum atom. Compounds 3 and 4 possess two dihexylaminophenyl substituents at their ends and differ by the number of platinum atoms in the oligomer "core" (one vs two in 3 and 4, respectively). The ligands have strong effective two-photon absorption cross-sections, while the heavy metal platinum centers give rise to efficient intersystem crossing to long-lived triplet states. Ultrafast transient absorption and emission spectra demonstrate that one-photon excitation of the chromophores produces an S1 state delocalized across the two conjugated ligands, with weak (excitonic) coupling through the platinum centers. Intersystem crossing occurs rapidly (Kisc approximately 1011 s-1) to produce the T1 state, which is possibly localized on a single conjugated fluorenyl ligand. The triplet state is strongly absorbing (epsilonTT > 5 x 104 M-1 cm-1), and it is very long-lived (tau > 100 micro s). Femtosecond pulses were used to characterize the two-photon absorption properties of the complexes, and all of the chromophores are relatively efficient two-photon absorbers in the visible and near-infrared region of the spectrum (600-800 nm). The complexes exhibit maximum two-photon absorption at a shorter wavelength than 2lambda for the one-photon band, consistent with the dominant two-photon transition arising from a two-photon-allowed gerade-gerade transition. Nanosecond transient absorption experiments carried out on several of the complexes with excitation at 803 nm confirm that the long-lived triplet state can be produced efficiently via a sequence involving two-photon excitation to produce S1, followed by intersystem crossing to produce T1.
为了探索具有强双光子吸收截面的铂乙炔发色团的光物理性质，我们研究了一系列铂乙炔配合物的合成与光谱表征，这些配合物具有被π供体或受体基团取代的高度π共轭配体。本工作中考虑的分子（编号为1 - 4）是双（苯乙炔基）双（三丁基膦）铂（II）配合物的类似物。分子1带有两个炔基 - 苯并噻唑基芴配体，分子2有两个炔基 - 二苯胺基芴配体与中心铂原子相连。化合物3和4在其末端具有两个二己基氨基苯基取代基，并且在低聚物“核心”中的铂原子数量不同（3和4中分别为一个和两个）。这些配体具有很强的有效双光子吸收截面，而重金属铂中心导致高效的系间窜越到长寿命的三重态。超快瞬态吸收和发射光谱表明，发色团的单光子激发产生一个在两个共轭配体上离域的S1态，通过铂中心的耦合较弱（激子耦合）。系间窜越迅速发生（Kisc约为1011 s-1）以产生T1态，该态可能定域在单个共轭芴基配体上。三重态具有很强的吸收（εTT > 5×104 M-1 cm-1），并且寿命很长（τ > 100 μs）。飞秒脉冲用于表征配合物的双光子吸收性质，并且所有发色团在光谱的可见光和近红外区域（600 - 800 nm）都是相对有效的双光子吸收剂。与单光子能带相比，这些配合物在比2λ更短的波长处表现出最大双光子吸收，这与由双光子允许的 gerade - gerade 跃迁引起的占主导地位的双光子跃迁一致。在803 nm激发下对几种配合物进行的纳秒瞬态吸收实验证实，长寿命的三重态可以通过涉及双光子激发产生S1，随后系间窜越产生T1的序列有效地产生。
