Synthesis and Near-infrared Luminescence of a Deuterated Conjugated Porphyrin Dimer for Probing the Mechanism of Non-radiative Deactivation

beta,meso,beta-Fused porphyrin oligomers have many attractive photophysical features such as strong absorption in the near-IR at wavelengths greater than 1000 nm, and high two-photon cross sections. However their ultrafast S1-S0 deactivation (kd 1011 s-1) limits potential applications. We have synthesised a deuterated fused porphyrin dimer to test whether deuteration influences the rate of non-radiative deactivation. An efficient synthetic strategy was developed, starting with deuteration of dipyrromethane. Deuteration of the zinc porphyrin dimer does not affect its fluorescence quantum yield in CD2Cl2(fD/fH= 1.00 ± 0.05). This implies that the ultrafast non-radiative deactivation is not simply a consequence of the small S1-S0 energy gap. Comparison with other conjugated porphyrin oligomers confirms that the deactivation rate in the edge-fused oligomers is faster than would be expected from the energy gap law. This result indicates that it should be possible to create near-IR dyes with similar S1-S0 energy gaps to the beta,meso,beta-fused porphyrin oligomers but with slower rates of S1-S0 decay.