Nonlinear optical response of cofacial phthalocyanine dimers and trimers

Abstract

The effects of intermacrocycle interactions on the second hyperpolarizabilities 〈γ(−ω;ω,−ω,ω)〉 of cofacial phthalocyanine dimers and trimers are studied. A theoretical analysis is presented based on the Frenkel exciton model for a chain of three level molecules. Using a simplified analysis in the static and near-resonant regimes we identify two mechanisms which lead to enhancements in the dimer or trimer value of 〈γ(−ω;ω,−ω,ω)〉 over that of the monomer. The first mechanism is a disruption of the balance between type I and type II terms in the sum over states expression for the second hyperpolarizability tensor γkjih(−ω;ω,−ω,ω), caused by weak intermacrocycle interactions. The second is a near-resonance enhancement of the type II terms due to an intermacrocycle interaction induced shift in the monomer derived two-photon allowed states towards twice the laser photon energy. This analysis is in good agreement with recent degenerate four wave mixing experiments [SPIE Proc. 2527, 61 (1995)] which showed a strong enhancement of 〈γ(−ω;ω,−ω,ω)〉 for SiPcO oligomers as a function of the number of macrocycles. Our calculations suggest that the first mechanism is responsible for the 25-fold monomer to dimer enhancement measured in this system, and that the additional 4-fold enhancement found in going from the dimer to the trimer is primarily the result of the second mechanism.

Synthesis and Optical Limiting Properties of Axially Bridged Phthalocyanines: [(tBu4PcGa)2O] and [(tBu4PcIn)2O]

“…As reported earlier, [5,6,8] the influence of different axial substituents on the electronic structure of the macrocycles of indium(iii) or gallium(iii) phthalocyanines is small. When compared with the UV/Vis spectra of [tBu 4 PcMCl] (M Ga, In), formation of the m-oxo metallophthalocyanine dimers 3 and 4 only leads to a weak (1 ± 2 nm) blue shift of the Q-band, which is attributed to exciton splitting in the dimer, [11] and to a red shift (1.5 nm) of the B-band. The red shift of the B-band is related to the interaction of the oxygen atom with the central metal, gallium or indium.…”

“…Compounds of this type may exhibit increased third-order nonlinearities in comparison with monomeric Pcs, owing to intramolecular interactions between the Pc rings. [11] Also, the optical limiting properties of 3 and 4 might be influenced by their dimeric structure. The m-oxo axially bridged unsubstituted [(PcGa) 2 O] [2] and [PcGaÀOÀAlPc] [12] dimers have been briefly mentioned in the literature, however they have not been further characterized.…”

Near-infrared two-photon absorption in phthalocyanines: Enhancement of lowest gerade-gerade transition by symmetrical electron-accepting substitution

“…[9][10][11][12] This implies the presence of 2PA-allowed transition in the above spectral range. [9][10][11][12] This implies the presence of 2PA-allowed transition in the above spectral range.…”

Strong nonlinear optical refractive effect of self-assembled multilayer films containing tetrasulfonated iron phthalocyanine

“…Manas [19] has succeeded in utilizing the Frenkel exciton model to quantitatively explain how intermacrocycle p-p interactions influence and enhance the nonresonant NLO response as in a thin film or oligomer. The experimental results validate the theory drawn by Manas and Spano in terms of Frenkel exciton model.…”