Dual fluorescence in 9-amino-2,7,12,17-tetraphenylporphycene

Abstract

The absorption spectrum of the asymmetric 9-amino-2,7,12,17-tetraphenylporphycene shows new, strongly red-shifted bands compared to the symmetric parental 2,7,12,17-tetraphenylporphycene and to the also asymmetric 9-acetoxy-2,7,12,17-tetraphenylporphycene. Dual emission is also observed with relative contributions that depend strongly on the excitation wavelength and temperature. The gap between the two fluorescence bands is 84 nm. Tautomerization in both the ground and excited states is shown to account for these observations, the 9-amino group being particularly able to selectively lower the energy of the first excited singlet state of just one of the trans tautomers. Introduction of amino groups in porphycenes may be a convenient way to gain a deeper insight into the tautomerization mechanisms in this macrocyclic core.

Tautomerization in 2,7,12,17‐Tetraphenylporphycene and 9‐Amino‐2,7,12,17‐tetraphenylporphycene: Influence of Asymmetry on the Direction of the Transition Moment

“…The same conclusion has been drawn previously, basing on different F 1 and F 2 fluorescence-decay times and on different excitation spectra in toluene and 2methyltetrahydrofuran. [32] Interestingly, whereas the excitation-and absorption spectra are very different for F 2 , they strongly resemble each other for F 1 .…”

“…We compare 2,7,12,17-tetraphenylporphycene (TPPo) with 9-amino-2,7,12,17-tetraphenylporphycene (9-ATPPo, Scheme 1). Previous studies of 9-ATPPo [32,33] revealed quite unique properties of this molecule. Dual fluorescence was observed and the energy gap between the two bands exceeded 1500 cm À1 .…”

Acid- and hydrogen-bonding-induced switching between 22-π and 18-π electron conjugations in 2-aminothiazolo[4,5-c]porphycenes

“…Of particular interest is the N-H tautomerization process in 9-substituted asymmetric porphycene derivatives as high electron-donating substituents in the 9-position leads to an enhanced energetic-splitting between the two transtautomers resulting in dual fluorescence emission. [17][18][19] In contrast,…”

“…No spectral changes could be observed in either case, which rules out protonation of the pyrrole nitrogens as the underlying cause for the observed results for ATAZPo 2 and sets this molecule apart of any porphycene reported so far. Prompted by our previous observations that the tautomers of asymmetric 9-amino porphycenes showed distinct red and near-IR absorption and fluorescence spectra, 17,18 we next considered the possibility that the two extreme spectra observed for the also asymmetric ATAZPo 2 could correspond to two tautomers as well, whose relative population would be affected by the solvent properties. The absorption spectra of 9-amino-2,7,12,17-tetrakis(2-methoxy ethyl) porphycene in HFIP and in THF (Fig.…”

“…Previously, we had observed dual emission in 9-substituted porphycenes and this was rationalised as resulting from inner-NH tautomerization. 17 11 and found to be of purity 495% by HPLC (see ESI †). All solvents used were of spectroscopic grade quality unless otherwise stated.…”