Unusual solvent dependent electronic absorption spectral properties of nickel(II) and copper(II) perhaloporphyrins

Abstract

Electronic absorption spectra of divalent metal (Ni(II) and Cu(II)) complexes of 2, 3,7,8,12,13,17,10,15, X = Br, Cl) were examined in various solvents. M(II) perhaloporphyrins exhibited dramatic shifts in their optical absorption spectral features relative to the corresponding metallotetraphenylporphyrins, MTPPs. Copper(II) perhaloporphyrins show significant red-shifts of the absorption bands in coordinating solvents relative to that observed for nickel(II) perhaloporphyrins. The large redshift of the electronic absorption bands and the gain in intensity of the longest wavelength band (Q(0,0)), of Cu(II) perhaloporphyrins in certain coordinating solvents is comparable to that found in meso-tetraphenylporphinatozinc(II), ZnTPP. The solvent dependent spectral features of M(II) perhaloporphyrins are attributed to a coordinative interaction of the solvent with the core metal ion induced by the electron deficient porphyrin macrocycle.

β‐Functionalized meso Tetrahalothien‐2‐ylporphyrins: Synthesis, Spectral, and Electrochemical Properties

“…This shows that on octabromination, the ruffling of the porphyrin ring (which is generally observed) give enough space for the meso substituted thienyl rings (which is relatively small compared to the phenyl ring in MTPP) to come more in plane with the porphyrin π‐ system. Similar to reported earlier in the case of copper octabromotetraphenylporphyrin, synthesized Cu5XThOBP showed a broad Soret band. A shoulder was observed for the Soret band in the lower wavelength region.…”

Femtosecond-Resolved Excited State Relaxation Dynamics of Copper (II) Tetraphenylporphyrin (CuTPP) After Soret Band Excitation

“…Actually, according to Sankar et al . 35 , about 40% of CuTPP in piperidine exist as the CuTPP:solvent adduct in the ground state while only 3% is measured to be present as an adduct in pyridine. In this aspect, the time constant of 300 fs may represent relaxation of the excited species which are prepared by Soret band excitation of the CuTPP-piperidine adduct which is already populated in the ground state.…”

“…Notably, red-shift of the Soret band is found to be quite large for CuTPP in piperidine. This could be attributed to solvent ligation of the ground-state CuTPP due to strong nucleophilicity of piperidine ( vide infra ) 32 , 35 . It is also noteworthy that Q(1,0) band is red-shifted by ~12 nm while oscillator strengths of Q(2,0) at 515 nm and Q(0,0) bands at 591 nm are much enhanced for CuTPP in piperidine compared to those in benzene.…”

Compounds with π(loc ) → π*(deloc ) electronic transitions and their solvatochromism

“…The solvatochromism of Cu(II) and Ni(II) metallotetraphenylporphyrins (Scheme ) as determined from their B absorption band by Bhyrappa et al . is described by Eqns and : with n = 21, r = 0.977, and sd = 43 cm –1 for CuTPP;…”

“…Based on the foregoing, the solvatochromism of π( loc ) → π*( deloc ) transitions should be governed by the polarizability of the medium and only scarcely influenced by its dipolarity. In order to ascertain whether this assumption can be generalized, we have examined the solvatochromism of some relevant systems containing pyrrole rings such as copper tetraphenylporphyrin (CuTPP) and nickel tetraphenylporphyrin (NiTPP), which were previously studied by Bhyrappa et al ., also several BODIPY's, and finally we have studied the solvathocromic behavior of a 7‐azaindole that is relevant as prototype of the DNA bases …”