Luminescent Pt(2,6-bis(N-methylbenzimidazol-2-yl)pyridine)X+: a comparison with the spectroscopic and electrochemical properties of Pt(tpy)X+ (X = Cl, CCPh, Ph, or CH3).,Dalton Transactions

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Luminescent Pt(2,6-bis(N-methylbenzimidazol-2-yl)pyridine)X+: a comparison with the spectroscopic and electrochemical properties of Pt(tpy)X+ (X = Cl, CCPh, Ph, or CH3).
Dalton Transactions ( IF 3.5 ) Pub Date : 2020-06-25 , DOI: 10.1039/d0dt01496f
Vikas M Shingade ₁ , Levi J Grove ₁ , William B Connick ₁

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A series of platinum(II) pincer complexes of the formula Pt(mbzimpy)X⁺, 1(a–d), (mbzimpy = 2,6-bis(N-methylbenzimidazol-2-yl)pyridine; X = Cl; (a), CCPh; (b), Ph; (c), or CH₃; (d), CCPh = phenylacetylide, and Ph = Phenyl) have been synthesized and characterized. Electronic absorption and emission, as well as electrochemical properties of these compounds, have been investigated. Pt(tpy)X⁺ analogs (tpy = 2,2′;6′2′′-terpyridine), 2(a–d), have also been investigated and compared. Electrochemistry shows that 1 and 2 analogs undergo two chemically reversible one-electron reduction processes that are shifted cathodically along the a < b < c < d series. Notably, these reductions occur at slightly higher negative potentials in the case of 1. The absorption spectra of 1 and 2 in acetonitrile exhibit ligand-centered (¹LC) transitions (ε ≈ 10⁴ M⁻¹ cm⁻¹) in the UV region and metal-to-ligand-charge transfer (¹MLCT) transitions (ε ≈ 10³ M⁻¹ cm⁻¹) in the visible region. The corresponding visible bands of 1b and 2b have been assigned to ¹(LLCT/MLCT) mixed state (LLCT: ligand-to-ligand-charge transfer). The preceding ¹LC and ¹MLCT transitions of 1 occur at lower energies than that of 2. These ¹LC transitions have distinctly been blue-shifted along a < c < d in 2, but occur at nearly identical energies in 1. Conversely, ¹MLCT transitions are red-shifted along a < c < d in both the analogs. The 77 K glassy solutions of 1 and 2 exhibit an intense vibronically-structured emission band at λ_max(0–0) in the 470–560 nm range. This band is red-shifted along b < a ≤ c < d in 1 and along a ≤ d ≈ c ≪ b in 2. The main character of these emissions is assigned to ³LLCT emissive state in 1b and 2b, whereas to ³LC in the rest of the compounds. Relative stabilization of these spin-forbidden emissive states is discussed by invoking configuration mixing with the higher-lying ³MLCT state.

中文翻译：

发光Pt（2,6-双（N-甲基苯并咪唑-2-基）吡啶）X +：与Pt（tpy）X +的光谱和电化学性质比较（X = Cl，CCPh，Ph或CH3）。

一系列铂（的II式）钳形络合物的Pt（mbzimpy）X ⁺，图1（a-d） ，（mbzimpy = 2,6-双（Ñ -methylbenzimidazol -2-基）吡啶; X =氯;（a），CCPh；（b），Ph；（c）或CH ₃；（d），CCPh =苯乙炔，Ph =苯基）已经合成并表征。已经研究了这些化合物的电子吸收和发射以及电化学性质。Pt（tpy）X ⁺类似物（tpy = 2,2'; 6'2''-叔吡啶）2（a–d）也已进行了研究和比较。电化学表明1和2类似物经历两个化学可逆的单电子还原过程，这些过程沿a <b <c <d系列进行阴极移位。值得注意的是，在1的情况下，这些降低发生在负电位稍高的位置。的吸收光谱1和2中显示出乙腈配体为中心的（¹ LC）转变（ε听，说：10 ⁴中号^-1厘米^-1）在UV区和金属-配体电荷转移（¹ MLCT）跃迁（ε ≈10 ³ M ^-1 cm ^-1）。对应的可见带1b和2b已分配给¹（LLCT / MLCT）混合状态（LLCT：配体到配体电荷转移）。前述^1个LC和^1个的MLCT跃迁1发生在比的较低能量2。这些^1个LC跃迁都明显是蓝移沿<C <d在2，但在几乎相同的能量发生1。相反，两个模拟物中的¹ MLCT跃迁均沿<c <d红移。的77K的玻璃态溶液1个2表现出强烈的vibronically结构发射带在λ_最大在470-560 nm范围内为（0-0）。沿B该带红移<一个≤ç<d在1和沿着≤d≈Ç«b在2。这些排放的主要字符被分配给³ LLCT发射状态在图1b和2b中，而以³ LC中的化合物的其余部分。通过调用与较高位置的³ MLCT状态混合的构型，讨论了这些自旋禁止发射态的相对稳定。

更新日期：2020-07-21

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