A series of tetraphenylporphyrins appended at the β-pyrrolic position with an ethynylphenylene- or ethynylpyridine-substituent have been subjected to spectroscopic and density functional theory (DFT) analyses. The mean absolute deviation between corresponding experimental and DFT-derived vibrational spectra is up to 10.2 cm(-1), suggesting that the DFT B3LYP/6-31G(d) method provides an accurate model of the β-substituted porphyrin systems. The configuration interactions that give rise to prominent electronic absorptions have been calculated using time-dependant DFT (TD-DFT) and have been rationalized with reference to the energy and topology of DFT calculated molecular orbitals. As the electron withdrawing capacity of the β-substituent increases the LUMO orbital gains appreciable amplitude over the substituent moiety and is stabilised. This represents a departure from the assumptions underpinning the Gouterman four-orbital model, resulting in atypical electronic absorption spectra. This phenomenon is also manifested in the enhancement patterns of the resonance Raman spectra insofar as B-band excitation engenders an enhancement of substituent based modes. These observations demonstrate that the β-substituent exerts an appreciable electronic influence on the porphyrin π-electron system and provides a means of introducing charge-transfer character to prominent electronic transitions.

Exfoliation of graphite was achieved using a free-base porphyrin 1 resulting in an efficient fabrication of single-layer nanographene (NG)- hybrid platelets that can be further functionalized with other nanomaterials. The novel nanographene-porphyrin hybrids reveal efficient charge transfer in the excited state.

A synthetic methodology for the synthesis of various β-pyrrolic-functionalised porphyrins and their covalent attachment to 2'-deoxyuridine and DNA is described. Palladium(0)-catalysed Sonogashira and copper(I)-catalysed Huisgen 1,3-dipolar cycloaddition reactions were used to insert porphyrins into the structure of 2'-deoxyuridine and DNA. Insertion of a porphyrin into the middle of single-stranded CT oligonucleotides possessing a 5'-terminal run of four cytosines was shown to trigger the formation of pH- and temperature-dependent i-motif structures. Porphyrin insertion also led to the aggregation of single-stranded purine-pyrimidine sequences, which could be dissociated by heating at 90 °C for 5 min. Parallel triplexes and anti-parallel duplexes were formed in the presence of the appropriate complementary strand(s). Depending on the modification, porphyrins were placed in the major and minor grooves of duplexes and were used as bulged intercalating insertions in duplexes and triplexes. In general, the thermal stabilisation of parallel triplexes possessing porphyrin-modified triplex-forming oligonucleotide (TFO) strands was observed, whereas anti-parallel duplexes were destabilised. These results are compared and discussed on the basis of the results of molecular modelling calculations.

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