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Cyclometalated complexes containing two or more metal centers were recently shown to offer photophysical properties that are advantageous compared to their mononuclear analogues. Here we report the design, synthesis, and luminescent properties of a dinuclear Ir­(III) complex formed by a ditopic N^C^N–N^C^N bridging ligand (L1) with pyrimidine as a linking heterocycle. Two dianionic C^N^C terminal ligands were employed to achieve a charge-neutral and nonstereogenic dinuclear complex 5. This complex shows a highly efficient red emission with a maximum at λem = 642 nm as measured for a toluene solution. The decay time and emission quantum yield of the complex measured for the degassed sample are τ = 1.31 μs and ΦPL = 80%, respectively, corresponding to the radiative rate of k r = 6.11·105 s–1. This rate value is approximately fourfold faster than for the green-emitting mononuclear analogue 3. Cryogenic temperature measurements show that the three substrates of the lowest triplet state T1 of 5 emit with decay times of τ­(I) = 120 μs, τ­(II) = 7 μs, and τ­(III) = 1 μs that are much shorter compared to those of the mononuclear complex 3, which has values of τ­(I) = 192 μs, τ­(II) = 65.6 μs, and τ­(III) = 3.6 μs. These data indicate that the spin–orbit coupling of state T1 with the singlet states is much stronger in the case of complex 5, which results in a much higher T1 → S0 emission rate. Indeed, a computational analysis suggests that in the dinuclear complex 5 the T1 state is spin–orbit coupled with twice the number of singlet states compared to that of mononuclear 3, which is a result of the electronic coupling of two coordination sites. The investigation of the temperature dependence of the emission rates of 3 and 5 shows that the room-temperature emission of both complexes is mainly contributed by a thermally populated excited state lying above the T1 state. To the best of our knowledge, complexes 3 and 5 are the first examples of Ir­(III) complexes that show photophysical behavior reminiscent of thermally activated delayed fluorescence (TADF).

The acoustic fiber sensor arrays that have been developed over the past two decades for oil exploration and other applications can support hundreds of fiber hydrophones per fiber pair and exhibit exceptional properties, including shot-noiselimited sensitivities better than 1 tradt\JHz, high stability, and dynamic ranges well in excess of 130 dB. This article reviews the main configurations reported to date, which are based on ladder architectures utilizing either Mach-Zehnder or Sagnac interferometric sensors and time-domain multiplexing. The emphasis is placed on their principles, performance characteristics, and relative advantages regarding such key issues as signal fading, polarization-induced fading, frequency response, sensitivity, and the number of sensors that can be multiplexed on a given pair of fibers.

We examine the signal-to-noise ratio (SNR) performance of a novel type of time domain multiplexed sensor arrays in which low gain (1-10 dB) fiber amplifiers are incorporated to compensate for splitting losses between sensors. The system noise figure for passive and amplified sensor arrays is presented, along with expressions to optimize the array parameters for high SNR's. We show that practical amplified sensor arrays exhibit low system noise figures that allow much larger arrays (hundreds of sensors) than passive arrays.

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