Photophysics of Threaded sp-Carbon Chains: The Polyyne is a Sink for Singlet and Triplet Excitation

Abstract

We have used single-crystal X-ray diffraction and time-resolved UV–NIR–IR absorption spectroscopy to gain insights into the structures and excited-state dynamics of a rotaxane consisting of a hexayne chain threaded through a phenanthroline macrocycle and a family of related compounds, including the rhenium(I) chlorocarbonyl complex of this rotaxane. The hexayne unit in the rhenium-rotaxane is severely nonlinear; it is bent into an arc with an angle of 155.6(1)° between the terminal C1 and C12 atoms and the centroid of the central C–C bond, with the most acute distortion at the point where the polyyne chain pushes against the Re(CO)3Cl unit. There are strong through-space excited-state interactions between the components of the rotaxanes. In the metal-free rotaxane, there is rapid singlet excitation energy transfer (EET) from the macrocycle to the hexayne (τ = 3.0 ps), whereas in the rhenium-rotaxane there is triplet EET, from the macrocycle complex 3MLCT state to the hexayne (τ = 1.5 ns). This study revealed detailed information on the short-lived higher excited state of the hexayne (lifetime ∼1 ps) and on structural reorganization and cooling of hot polyyne chains, following internal conversion (over ∼5 ps). Comparison of the observed IR bands of the excited states of the hexayne with results from time-dependent density functional calculations (TD DFT) shows that these excited states have high cumulenic character (low bond length alternation) around the central region of the chain. These findings shed light on the complex interactions between the components of this supramolecular rotaxane and are important for the development of materials for the emerging molecular and nanoscale electronics.

Monitoring one-electron photo-oxidation of guanine in DNA crystals using ultrafast infrared spectroscopy

“…19 The presence of these bands, in the absence of DNA direct excitation has been observed in a number of previous TRIR studies of metal complex intercalating systems 6,[20][21][22][23][24] and is attributed to a perturbation of groundstate vibrations due to an electrostatic (Stark) effect [25][26] that arises because of changes in the charge distribution of the neighbouring molecule upon excitation. [26][27][28][29] As this effect is known to be localised (typically < 6 Å) the bleached bands therefore report on the immediate surroundings of the excited state. [25][26][27][28][29] These changes can be correlated with the crystal structure as follows.…”

“…[26][27][28][29] As this effect is known to be localised (typically < 6 Å) the bleached bands therefore report on the immediate surroundings of the excited state. [25][26][27][28][29] These changes can be correlated with the crystal structure as follows. There are two distinct guanine-containing sites:-(1) The G 9 base is stacked onto the central pyrazine ring of the intercalated dppz ligand at the terminal T 1 C 2 :G 9 A 10 step (Fig.…”

Carbyne: The Molecular Approach

“…[89] Since this time, others have also embraced this concept, and a variety of polyyne rotaxanes have been constructed over the past few years. [90][91][92] …”

Calculating singlet excited states: Comparison with fast time-resolved infrared spectroscopy of coumarins

“…[12][13][14][15][16][17][18][19] Despite its growing popularity, TDDFT has many associated problems and has been shown to be inaccurate for long-range charge transfer, 20,21 Rydberg, 22,23 and core excitations, 24 when using common forms for the exchange-correlation functional. This has led to the development of range-separated functionals which can rectify many of these problems, albeit with an increase in computational cost.…”