We present a multipurpose computer code MesoBioNano Explorer (MBN Explorer). The package allows to model molecular systems of varied level of complexity. In particular, MBN Explorer is suited to compute system's energy, to optimize molecular structure as well as to consider the molecular and random walk dynamics. MBN Explorer allows to use a broad variety of interatomic potentials, to model different molecular systems, such as atomic clusters, fullerenes, nanotubes, polypeptides, proteins, DNA, composite systems, nanofractals, and so on. A distinct feature of the program, which makes it significantly different from the existing codes, is its universality and applicability to the description of a broad range of problems involving different molecular systems. Most of the existing codes are developed for particular classes of molecular systems and do not permit multiscale approach while MBN Explorer goes beyond these drawbacks. On demand, MBN Explorer allows to group particles in the system into rigid fragments, thereby significantly reducing the number of dynamical degrees of freedom. Despite the universality, the computational efficiency of MBN Explorer is comparable (and in some cases even higher) than the computational efficiency of other software packages, making MBN Explorer a possible alternative to the available codes.

Radiation damage following the ionising radiation of tissue has different scenarios and mechanisms depending on the projectiles or radiation modality. We investigate the radiation damage effects due to shock waves produced by ions. We analyse the strength of the shock wave capable of directly producing DNA strand breaks and, depending on the ion's linear energy transfer, estimate the radius from the ion's path, within which DNA damage by the shock wave mechanism is dominant. At much smaller values of linear energy transfer, the shock waves turn out to be instrumental in propagating reactive species formed close to the ion's path to large distances, successfully competing with diffusion.

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Much effort has been dedicated to increase the operational lifetime of blue phosphorescent materials in organic light-emitting diodes (OLEDs), but the reported device lifetimes are still too short for the industrial applications. An attractive method for increasing the lifetime of a given emitter without making any chemical change is exploiting the kinetic isotope effect, where key C-H bonds are deuterated. A computer model identi ed that the most vulnerable molecular site in an Ir-phenylimidazole dopant is the benzylic C-H bond and predicted that deuteration may lower the deactivation pathway involving C-H/D cleavage notably. Experiments showed that the device lifetime (T 70 ) of a prototype phosphorescent OLED device could be doubled to 355 hours with a maximum external quantum e ciency of 25.1% at 1000 cd/m 2 . This is one of the best operational performances of blue phosphorescent OLEDs observed to date in a single stacked cell.

In this paper we suggest a theoretical method based on the statistical mechanics for treating the α-helix↔random coil transition in alanine polypeptides. We consider this process as a first-order phase transition and develop a theory which is free of model parameters and is based solely on fundamental physical principles. It describes essential thermodynamical properties of the system such as heat capacity, the phase transition temperature and others from the analysis of the polypeptide potential energy surface calculated as a function of two dihedral angles, responsible for the polypeptide twisting. The suggested theory is general and with some modification can be applied for the description of phase transitions in other complex molecular systems (e.g. proteins, DNA, nanotubes, atomic clusters, fullerenes).

Low operational stability is the main limiting factor for commercialization of the blue phosphorescent organic light emitting diodes (PhOLEDs). The high energy and long lifetime of triplet excitons in blue PhOLEDs makes them more prone to degradation. Degradation of the host molecules in the emitting layer of PhOLEDs is one of the possible mechanisms leading to the luminosity loss in the course of device operation. Although possible degradation mechanisms are proposed in the literature, predicting the degradation kinetics is not straightforward because the evolution of excited states should be accurately described. We propose a computational scheme to assess the operational stability of PhOLED host materials. Our protocol relies on the usage of the multireference CASSCF/XMCQDPT2 method. In the present work we consider the degradation of four prototypical blue PhOLED host molecules in the charged and excited states as well as the degradation induced by exciton–polaron and exciton–exciton annihilation processes with the focus on breaking of exocyclic C–C or C–N bonds and triazine ring fission. By analyzing the calculated activation energies for different mechanisms we found the least stable states and the most probable dissociation pathways. On the basis of our computations, we derived a stability series for the studied molecules and determine the structural features that provide higher stability with respect to the unimolecular dissociation.

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