Ultrafast nonlinear optical studies of cyclo[4]naphthobipyrroles

Abstract

Expanded porphyrins belong to the class of porphyrinoids, where the core of the porphyrin macrocycle is increased either by incorporating additional pyrrolic units, or by increasing the number of bridging carbon atoms from more than four, or a combination of both. The significance of these classes of compounds lies in their novel photophysical and nonlinear optical properties. Superior nonlinear optical coefficients are usually observed for aromatic expanded porphyrins with large number of π-electrons owing to their distinct structural features. In this regard, cyclo[8]pyrrole is unique, owing to its large planar 30-π core macrocyclic ring in its diprotonated state. Here, all the eight pyrrole units are directly linked to each other through their á-positions. Recently, we have synthesized, cyclo[4]naphthobipyrroles, a unique class of cyclo[8]pyrroles, where alternate pyrrole units are fused with naphthalene moieties. This adds more rigidity to the resultant cyclo[8]pyrrole while further extending the resultant π-conjugation. Herein, we present some of our results from the picosecond nonlinear optical studies of a β-octa-isopropyl-cyclo[4]naphthobipyrrole. The nonlinear optical coefficients were extracted from the Z-scan measurements. The values of two-photon cross-sections obtained for these molecules were in the range of 10 4 GM. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).