Click Reaction Synthesis and Photophysical Studies of Dendritic Metalloporphyrins

Abstract

Several dendritic zinc(II)‐porphyrins bearing carbazole units at the terminals have been prepared through click reaction of azide‐substituted Zn‐porphyrin precursors and carbazole‐based alkynes under [Cu(NCCH3)4][PF6] catalysis. This family of new dendritic metalloporphyrins shows dual luminescence from both the upper S2 and the lowest S1 singlet states. The observed trends in the spectroscopic data and the photophysical properties of the dendrimers have been rationalized in terms of the type of meso‐spacer between the macrocycle and dendritic shell. The key feature of the meso‐spacer is proposed to be the degree of hindrance towards aryl ring rotation relative to the mean porphyrin plane. Based on the observed differences in the S1→S0 fluorescence quantum yield on going from four‐ to five‐coordinate dendrimers, it was shown that dendrimer architectures with all four meso‐aryl spacers sterically hindered, are most appropriate to monitor processes related to axial ligation of the dendrimer core, since they provide larger luminescence response differences between the four‐coordinate and five‐coordinate forms. The blue S2→S0 fluorescence quantum yield has been measured and the observed trend has been rationalized in terms of the S2→S1 energy gap law. No significant differences were observed between the compounds either with different rotational degree of freedom of the meso‐spacers or with different ligation states of the dendrimer core.

Binding ability of first and second generation/carbazolylphenyl dendrimers with Zn(ii) tetraphenylporphyrin core towards small heterocyclic substrates

“…Zn(II) tetraphenylporphin (ZnTPP) was taken as the object of comparison. The compounds ZnD4-G1, ZnD5-G1, ZnD6-G1, ZnD7-G2, ZnD8-G2, ZnD9-G2 were previously synthesized 18 as new uorescent switches and photoactive devices for detection of substrates of different nature.…”

Excitation energy deactivation funnel in 3-substituted BODIPY-porphyrin conjugate

“…T = 293 K, optical path length is 1 cm.Thus, both the porphyrin and BODIPY moieties seem to keep their own spectral features upon formation of the conjugate 12 , indicating weak electronic coupling between the two molecular fragments. The weak spectral shifts observed in the BODIPY-porphyrin conjugate spectra in going from toluene to THF are due to: a) the transition from a planar 4-coordinated form to a dome-shaped 5-coordinated form upon ligation of the chelated Zn ion with the THF molecule;13 b) the solvent influence on the BODIPY absorption. 14 The fluorescence excitation spectra of the BODIPY-porphyrin conjugate 12 measured at three emission wavelengths in both toluene (Figure 2a)and THF(Figure 2b)do not reveal any differences in the spectral shape.…”

Spectral-Luminescent Properties of meso-Tetraarylporphyrins Revisited: The Role of Aryl Type, Substitution Pattern and Macrocycle Core Protonation

“…[19][20][21][22][31][32][36][37][38] The synthesis and properties of different series of porphyrin compounds with sequential attachment of meso-aryl groups or the exchange of aryl groups of one type with those of another type have been widely reported. It was shown that the changes of numerous photophysical and physico-chemical properties of the studied meso-arylporphyrins, including the nonlinear two-photon absorption cross section, [39] the molecular contraction upon triplet state formation, [40] the fluorescence quantum yield from the lowest and higher excited states, [36,[41][42] the shift of the bands in the absorption spectra, [41][42][43] and the rates of radiative and nonradiative excitation energy deactivation pathways, [36,[41][42][43] can be interpreted as being "additive" with respect to the number of attached/replaced aryl groups. However, it needs to be stressed that all of these dependencies relate to the porphyrin free bases or metallocomplexes.…”

“…[36,38,[41][42][43] Having the aim to go further into the role of the "ortho effect" of aryl substituents we have prepared the series of symmetrical and asymmetrical 5,10,15,20- Figure 4). In this series, the substitution architecture was used as a tool to modulate the sterical hindrances over macrocycle.…”