Theoretical Study and Luminescence Properties of the Cyclic Cu₃(dppm)₃OH²⁺ Cluster. The First Luminescent Cluster Host at Room Temperature

Abstract

The [Cu(3)(dppm)(3)OH](BF(4))(2) cyclic cluster host is found to be luminescent at 298 K (lambda(max) = 540 nm; tau(e) = 89 +/- 9 &mgr;s; Phi(e) = 0.14 +/- 0.01) in degassed ethanol solutions and at 77 K (lambda(max) = 480 nm; tau(e) = 170 +/- 40 &mgr;s; Phi = 0.73 +/- 0.07) also in ethanol. The nature of the lowest energy excited states has been addressed theoretically using density functional theory and experimentally using UV-visible, luminescence, and polarized luminescence spectroscopy and is found to be (1,3)A(2) arising from the.(18e)(4)(7a(2))(1)(13a(1))(1) electronic configuration. The excited state geometry optimization for the model Cu(3)(PH(3))(6)OH(2+) compound in its T(1) state ((3)A(2)) has been performed using density functional theory and compared to its ground state structure. The Cu.Cu bond length is expected to decrease greatly in the excited state (calculated DeltaQ approximately 0.47 Å), in agreement with the d(10) electronic configuration. The perturbation of the photophysical properties by the addition of two guest carboxylate anions has been investigated. From the Stern-Volmer plots, the quenching constants, k(q), are 1.65 x 10(8) and 5.10 x 10(8) M(-)(1) s(-)(1) for acetate and 4-aminobenzoate, respectively, which are also proportional to the relative binding strengths of the substrates with Cu(3)(dppm)(3)OH(2+) (i.e., acetate < 4-aminobenzoate).

Photoinduced oxidative degradation of unsaturated M3(dppm)3CO2+ clusters (M = Pd, Pt) by chlorocarbons and chloride ion

“…3). It is also close to the distance found experimentally in the ~d , ( d~~m ) ,~~' + cluster in its lowest energy triplet excited state ( A,; -2.78 A) (35). If a formal electron is indeed transferred from the Pd3,+ to the C1' center to form the Pd3,+ and C1-species, then the calculated Pd-Pd bond length in P~,(PH,),(CO)(C~)~+ should be close to 2.73 A also.…”

“…For ~d~( d~~m )~~0~+ in its ground ('A,) and lowest energy triplet excited states (,A,, (TI), 3~2 (T2)), the geometry compounds have already been computed (35). The computations compared very favorably with the experimental data, particularly for the Pd-Pd bond lengths.…”

“…This general behavior has also been observed for metal complexes of calix [4]arene derivatives for which a metal atom is located at the lower rim acting either as a luminescent probe (Ir(1); ref. 30) or a strong Lewis acid (W = 0 (31)), and the recently investigated ~u , ( d p p m ) , 0~~+ cluster (32). This phenomenon is attributable to the "loose bolt effect" (for small perturbations) or to the formation of an "exciplex" (for larger change in lifetimes) (33).…”

“…"Data for Pd,(PH,),(CO)(CI)' are also compared In Table 3, and data for Pd,(PH,),(CO)" are from ref. 35. All calculat~ons were performed under a C,, restricted geometry.…”

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“…± The Cu I complexes show pseudotetrahedral symmetry, and 1 H-NMR data support the existence of Cu I in 1 and 2. Conclusions.…”