Abstract
The photophysical and photochemical properties of phthalocyanine and naphthalocyanine with similar structures were studied in solution and with density-functional theory (DFT) computational method. The extended π-conjugated system in naphthalocyanines causes a bathochromic shift in UV-Vis, emission and excitation bands, and promotes lesser generation of singlet oxygen in solution when compared to phthalocyanines. Time dependent DFT (TD-DFT) calculations point out the molecular orbitals involved in Q-band transition, corresponding to highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) transition with a concentration of charge along x-axis, while the transition to LUMO+1 is in y-axis direction. The presence of tert-butyl substituents does not affect the molecular orbitals shape, but affect their energies. Aggregation studies in dimethyl sulfoxide (DMSO):water solutions showed that naphthalocyanines studied have more aggregation tendency than the phthalocyanines. DFT studies indicated that stacked-dimers are preferred to rotated-stacked conformation due the interaction between ZnII and nitrogen atom from different monomers.
Highlights
Naphthalocyanines (Nc) are phthalocyanines derivatives with extended π-conjugated system, which promotes a bathochromic shift in their absorption bands (750‐900 nm).[1,2]
Theoretical absorption spectra calculated with TD-density-functional theory (DFT)/B3LYP/6-311G(d,p) in dimethyl sulfoxide (DMSO) for (a) Zinc phthalocyanine (ZnPc) and (b) ZnNc
In our study we describe the photophysical and photochemical properties phthalocyanine and naphthalocyanines with similar structures to understand the effects of extended π-conjugation on compounds
Summary
Naphthalocyanines (Nc) are phthalocyanines derivatives with extended π-conjugated system, which promotes a bathochromic shift in their absorption bands (750‐900 nm).[1,2] Both macrocycles are widely applied as industrial dyes, in solar cells,[3] nonlinear optics,[4] electrochromic devices,[5] photodynamic therapy (PDT)[6] and chemical sensors.[7]Phthalocyanines (Pc) and naphtalocyanines have a high tendency to aggregate, especially in aqueous solution. In order to give insight on how absorption spectrum at low concentrations of phthalocyanine is affected by the presence of aggregates, we performed DFT calculations by means of BLYP functional and 6-311G(d) basis set with Grimme’s correction for dispersion interactions (D3-BJ)[24,25] as implemented in ORCA software[26] for dimers of ZnPc and ZnNc. We started geometry optimization with different stacking conformations, by changing the rotation angle of one monomer in relation to the other.
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