Effect of alkyl substituents on the quasibright-line spectra of porphyrines

Electronic spectra of cationic forms of meso-tetrapropylporphin in a nanoporous silicate gel matrix

“…2b, curve 3) and is narrowed by practically a factor of two (∆ν ≈ 390 cm -1 ). In this case, in contrast to H 2 TPP, the fluorescence spectrum of which in n-octane at 77 K and 4.2 K has a quasi-line structure [17,30], the low-temperature fluorescence spectrum of H 4 TPP 2+ remains broadband in an acidified n-octane solution. As shown by experiments, the use of selective laser excitation (He-Ne laser, λ ex = 632.8 nm) at 4.2 K also does not lead to the appearance of a fine-structure fluorescence spectrum for H 4 TPP 2+ in n-octane+CF 3 COOH.…”

“…1c), the nature of which depends on the isomer structure of the molecule. Most likely the complex "multiplet" structure of the quasi-line fluorescence and absorption spectra for H 2 TPP in n-octane [30] is a consequence of the existence of a large number of isomers for the molecule in liquid solution, which are fixed when the n-octane matrix is rapidly frozen (in [17] it is shown that equilibrium conditions for the formation of a single-crystal n-octane matrix simplify the "multiplicity" of the quasi-line spectra).…”

“…Let us begin with the fact that for the H 2 TPP free base, the frequencies of vibrations predominantly localized on the pyrrole rings are close to the frequencies for H 2 P [15][16][17]30]. Therefore we can follow the appearance of their related vibrations in the fine-structure fluorescence spectra of H 4 P + in CF 3 COOH [35] and the gel matrix [9] on the one hand, and on the other hand in the spectrum of H 4 TPP 2+ in the gel matrix.…”