In this article we characterise the radiationless decay of the first few electronic excited states of the cations of DNA/RNA nucleobases uracil and thymine, including the effects of dynamic electron correlation on energies and geometries (optimised with XMS-CASPT2).

Photoionisation in DNA, i. e. the process of photoinduced electron removal from the chromophoric species -the nucleobases -leading to their cationic form, has been scarcely studied despite being considered to be responsible for significant damaging instances in our genetic material. In this contribution we theoretically characterise the electronic ground and excited state decay pathways of cationic DNA nucleobase cytosine + and its epigenetic derivative 5-methyl-cytosine + , including the effects of dynamic electron correlation on energies and geometries of minima and conical intersections. We do this by comparing the results of XMS-CASPT2 calculations with CASSCF estimates and we find some significant differences between the results of these two methods. In particular, including dynamic electron correlation is found to significantly reduce the barrier to access the ðD 1 =D 0 Þ conical intersection. We find notable similarities in both cytosine and 5methyl-cytosine cations, and accessible conical intersections in the vicinity of the Franck-Condon region are found. This points towards an ultrafast depopulation of their electronic excited states. Moreover, the shape of the ground state potential energy surface strongly directs the decaying excited state population towards the cationic ground state minimum on ultrafast timescales, preventing photo-fragmentation and thus explaining their photostability. To better compare our calculations with the available experimental data we compute the UV (ground and excited state) and IR absorptions.[a] Dr.

A recent implementation of time-dependent tight-binding density functional theory is employed in excited state molecular dynamics for the investigation of the fluorescence quenching mechanism in 3 prototypical aggregation-induced emission systems.

The (15-oxo-3,7,11-triazadispiro[5.1.5.3]hexadec-7-yl)oxidanyl, a bis-spiropiperidinium nitroxide derived from TEMPONE, can be included in cucurbit[7]uril to form a strong (K(a)∼ 2 × 10(5) M(-1)) CB[7]@bPTO complex. EPR and MS spectra, DFT calculations, and unparalleled increased resistance (a factor of ∼10(3)) toward ascorbic acid reduction show evidence of deep inclusion of bPTO inside CB[7]. The unusual shape of the CB[7]@bPTO EPR spectrum can be explained by an anisotropic Brownian rotational diffusion, the global tumbling of the complex being slower than rotation of bPTO around its "long molecular axis" inside CB[7]. The CB[7] (stator) with the encapsulated bPTO (rotator) behaves as a supramolecular paramagnetic rotor with increased rotational speed of the rotator that has great potential for advanced nanoscale machines requiring wheels such as cucurbiturils with virtually no friction between the wheel and the axle for optimum wheel rotation (i.e. nanopulleys and nanocars).