Effect of Axial Substitution on the Optical Limiting Properties of Indium Phthalocyanines

Abstract

Nonlinear absorption, refraction, and optical limiting by a series of monoaxially chloro- and aryl-substituted indium(III) phthalocyanines are described. The absorption cross sections and temporal evolution of the low-lying excited states are also reported. A large nonlinear absorption that increased with wavelength between 500 and 590 nm was observed in each material. The nanosecond nonlinear absorption and the optical limiting are shown to be dominated by a strong excited state absorption from an orientationally averaged triplet state. We derive and experimentally confirm the relation between the molecular absorption cross sections and the fluence-dependent nonlinear absorption coefficients. The effective nonlinear refraction on the nanosecond time scale was reduced because the electronic contribution to the nonlinear refractive index was of the opposite sign from the thermal contribution. An optical limiter using the new material, p-(trifluoromethyl)phenylindium(III) tetra-tert-butylphthalocyanine [(t-Bu)4PcIn(p-TMP)], showed a much lower threshold for optical limiting and a much lower transmission at high fluences than previously reported indium phthalocyanine limiters. This improved optical limiting was due both to the larger nonlinear absorption coefficient and to the design of the limiter device. The optical properties of the In phthalocyanine moiety were found to be surprisingly robust to structural changes in the axial position.

New axially aryloxy substituted gallium phthalocyanines for nonlinear optics

“…5,6 Among the large number of NLO absorbers that have been identified so far, phthalocyanines are especially attractive because of their great reverse saturable absorption (RSA) properties, and are still being investigated to improve their optical limiting properties and to expand their optical limiting window from the visible to the near IR range. 6,7,9 In this communication, we report on the synthesis and nonlinear optical (including optical limiting) properties of new axially aryloxy substituted and bridged gallium phthalocyanines. As a result, axial substitution and dimerization of the gallium phthalocyanine monomer resulted in significant reductions in the saturation energy density of the material displaying clear evidence of the usefulness of structurally modifying the gallium phthalocyanine unit.…”

“…It also defocused the beam to its largest waist radius displaying its competitiveness as a potential optical limiter. Gallium and indium 6,7,9 phthalocyanines are amongst the most promising that have been investigated as limiters of intense light and the current series presents a selection of structural modifications useful for varying their nonlinear optical properties. Fig.…”

Conjugated Molecules for the Smart Filtering of Intense Radiations

“…The origin of the nonlinear transmission in phthalocyanines is related mostly with the occurrence of the absorption of an excited state [27], and less preponderant, by the verification of nonlinear refraction [28]. The mechanism of nonlinear absorption in phthalocyanines is successfully interpreted in terms of the four-level model [29].…”

“…At a certain point the irradiated molecule reaches a critical state of electronic polarization, which is capable to get in resonance at the wavelength of irradiation. Such a resonance of a highly polarized phthalocyanine molecule is believed to involve a MLCT/LMCT process which is red-shifted with respect to the same kind of transition in the ground state [28]. The deformability of the π-electrons cloud upon irradiation can be expressed as a generalized π-electrons…”

One- and two-photon absorption of highly conjugated multiporphyrin systems in the two-photon Soret transition region

“…3 Of the many candidate materials for these applications, porphyrins are among the most highly polarizable organic molecules reported to date, and because of their enhanced nonlinear susceptibilities, 4-9 they are promising molecules for optical limiters, [10][11][12][13][14] for photodynamic therapy, 15 and as contrast agents for in vivo imaging and microscopy. [16][17][18][19] Highly conjugated multiporphyrin chromophores possess large third-order nonlinear susceptibilities, ͑3͒ .…”