Electronic structure and photophysics of (C=C)tetra-p-tolylporphyrin2+.

The electronic structure and photophysical properties of (C=C)TTP(2+) (TTP = tetra-p-tolylporphyrin) were scrutinized by using quantum mechanical calculations and transient absorption spectroscopic measurements. When compared to a metalloporphyrin, the presence of the C=C unit in (C=C)TTP(2+) causes a splitting of the degenerate LUMO and a large decrease in the HOMO-LUMO gap, while the 2+ charge and tolyl groups lead to additional charge-transfer-like transitions in the visible absorption spectrum. The small HOMO-LUMO gap and ruffled structure lead to a very short excited-state lifetime of 10 ± 0.3 ps.