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The electronic and photophysical properties of these materials can be generally tuned by the substituent effect of the end groups, the number of conjugated units, and also by the possibility to functionalize them for connections with other device components such as metal clusters/tips, σ-bonded, or π-coordinated metal centres, which gives rise to the cumulene chain stabilization, as well as photosensitizers, ligands for target receptors, etc. Cumulenes and polyynes can also be applied in organic light-emitting devices, liquid crystals, and photodynamic therapy. These compounds exhibit electrochromism due to low operational driving voltage to change the colour and simultaneously guarantee high contrast and good reversibility of their redox states. The other applications of cumulenes and polyynes include optoelectronics, since the π-electrons in conjugated systems are the source of large nonlinearity in the optical response of the material. Cumulenes and polyynes are interesting moieties for molecular junctions because (i) the appropriate length of the molecules (10–30 Å) is close to the distance used in the scanning tunnelling microscopy, (ii) their rigidity and length-persistence allow for minimizing geometry fluctuations of the molecule within the junction, and (iii) it is relatively easy to avoid molecular aggregations and unwanted cross-linking between the units in the junctions. Out of many classes of π-conjugated conducting organic materials, the one -dimensional sp-hybridized, linear molecules, such as polyynes and cumulenes, can find use as semiconducting nanowires for nanoelectronic devices.
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This is why it is important to precede high-cost experimental research with less expensive, pilot, theoretical calculations. Hence, a great number of measurements must be compiled into a conductance histograms showing the distribution of the measured values. However, experimentally, it is hard to obtain unambiguous conductance data because of molecular flexibility which makes the geometry of the device fuzzy at the nanoscale. Especially, factors determining the charge transport through the single-molecule junctions are essential for the development of sensors, thermoelectric devices, logic operations, and information storage on molecular devices. Constructing efficient and stable molecular nano-devices is one of the urgent needs of material science oriented chemistry.