Computational quantum chemistry applied to photochemistry, Group 14 chemistry and molecular electronics
The project is divided into two main parts; the first is directed towards aromaticity effects in electronically excited states, and the second towards design of silicon based single-molecule electronics components. In both parts we will apply quantum chemical calculations using DFT and electron correlated wave function methods (primarily coupled cluster methods), and the calculations are closely connected to on-going experimental studies in the group. The first topic concerns excited state aromaticity and is based on Baird's rule which tells that species with 4npi-electrons are aromatic and those with 4n+2 are antiaromatic in the lowest pipi* excited triplet and singlet states. A series of processes and properties can be examined and rationalized in terms of excited state aromaticity. In the next we will use calculations to (i) examine singlet state homoaromaticity, i.e., aromaticity where the aromatic cycle in part goes through space, (ii) design of new compounds with low singlet-triplet energy gaps, (iii) explore novel high-spin molecules which could be used in molecular magnets (iv) investigate the influence of excited state aromaticity on photochemical reactivity. In the second topic we design and test organosilicon based compounds in charge transport junctions. The channels for charge transport in the compounds that we design mostly exploit non-standard conjugation topologies, in contrast to the regular pi-conjugated molecules investigated by other groups. Whereas charge transport calculations are performed by collaborators we compute the fundamental electronic and optical properties of the compounds. We also examine cross-hyperconjugation and hyperomniconjugation, conjugation topologies in which saturated (conductive) molecular segment are inserted into pi-conjugated molecules.