Spectral and Photophysical Properties of Ethylene-Bridged Side-to-Side Porphyrin Dimers. 1. Ground-State Absorption and Fluorescence Study and Calculation of Electronic Structure of trans-1,2-Bis(meso-octaethylporphyrinyl)ethene

• Published in: Journal of physical chemistry (1952) 1996-08, Vol.100 (32), p.13857-13866
• Main Authors: Chachisvilis, Mirianas, Chirvony, Vladimir S, Shulga, Alexander M, Källebring, Bruno, Larsson, Sven, Sundström, Villy
• Format: Article
• Language: English
• ISSN: 0022-3654; 1541-5740
• DOI: 10.1021/jp9607374

We have studied a double-bond bridged porphyrin dimer, trans-1,2-bis(meso-octaethylporphyrinyl)ethene (tbisOEP), which in solutions exhibits new spectral properties:  (i) pronounced absorption bands in addition to the monomer ones are observed in the 480−500 and 600−900 nm regions; (ii) a broad-band fluorescence with a viscosity-dependent intensity and spectral position is detected in the near-IR region (750−1100 nm). An investigation of fluorescence excitation spectra, combined with semiempirical quantum chemical calculations and geometry optimizations suggest that in solution tbisOEP exists in two main conformations, which we name conformers P and U. The ratio of their concentrations was estimated to be approximately 5:1 in toluene at room temperature. The P conformer was found to be responsible for the “usual” monomer-type absorption bands (Soret and Q) in the tbisOEP absorption spectrum, whereas the U conformer is responsible for the additional absorptions in the 480−500 and 600−900 nm regions. The unusual near-IR fluorescence originates from the U conformer and its quantum yield (Φ) is 6 × 10-4 in toluene. Increase of solvent viscosity results in a strong blue-shift of the near-IR emission and increase of its intensity (Φ = 4 × 10-3 in paraffin oil). Both conformers P and U were found to exhibit very short exited-state lifetimes (