Abstract
Fusion of two N-annulated perylene (NP) units with a fused porphyrin dimer along the S-0-S-1 electronic transition moment axis has resulted in new near-infrared (NIR) dyes 1a/1b with very intense absorption (epsilon>1.3x10(5)M(-1)cm(-1)) beyond 1250nm. Both compounds displayed moderate NIR fluorescence with fluorescence quantum yields of 4.4x10(-6) and 6.0x10(-6) for 1a and 1b, respectively. The NP-substituted porphyrin dimers 2a/2b have also been obtained by controlled oxidative coupling and cyclodehydrogenation, and they showed superimposed absorptions of the fused porphyrin dimer and the NP chromophore. The excited-state dynamics of all of these compounds have been studied by femtosecond transient absorption measurements, which revealed porphyrin dimer-like behaviour. These new chromophores also exhibited good nonlinear optical susceptibility with large two-photon absorption cross-sections in the NIR region due to extended -conjugation. Time-dependent density functional theory calculations have been performed to aid our understanding of their electronic structures and absorption spectra.