Spectroscopic and Nonlinear Optical Properties of 3, (4-tert-butylphenoxy) Phthalocyanine Constitutional Isomers

Introduction

Organic material with second-order nonlinear optical (NLO) material properties are useful in applications such as optical data processing or storage devices and can be easily processed and integrated into optical devices [1, 2]. Organic materials such as phthalocyanines (Pcs) exhibit large and fast nonlinearities, which can be fine-tuned by rational modification of the molecular structure [3, 4, 5]. Pc molecules are known to have large third-order optical nonlinearities which arise from the highly delocalised two dimensional 18-electron system [6, 7, 8, 5]. Pcs have been intensively investigated for their NLO properties. In most studies, NLO properties of tetra substituted Pcs have been studied as a mixture of isomers [9].

Aims

In this work four constitutional isomers of unmetalated tert-butylphenoxy phthalocyanine were separated and their NLO properties measured, in order to identify which isomer contributes the most to the measured NLO response.This work presents spectroscopic and nonlinear optical properties of unmetalated 3, (4-tert-butylphenoxy) phthalocyanine constitutional isomers. Second order nonlinear polarizability, second order hyperpolarizability and third order imaginary susceptibility (Im[χ⁽³⁾]) values were determined for monomeric and aggregated constitutional isomers.

Z-scan technique is employed in determining the second order NLO property. Spectroscopic and photophysical properties of the isomers, such as fluorescence lifetime and rotational correlation lifetimes are determined. Magnetic circular dichroism (MCD), time correlated single photon counting spectroscopy (TCSPC), ultra-violet visible (UV/vis) spectroscopy,   Infra-red (IR) spectroscopy and density functional theory (DFT) are some of the techniques used to characterise physical properties of the isomers.

References

1. G. de la Torre, P. Va´zquez, F. Agullo´-Lo´pez, T. Torres, J. Mater. Chem., 1998, 8, 1671-1683.
2. T. Verbiest, S. Houbrechts, M. Kauranen, K. Clays, A. Persoons, J. Mater. Chem., 1997, 7, 2175-2189
3. J. M. Fox, T. J. Katz, S. V. Elshocht, T. Verbiest, M. Kauranen, A. Persoons, T. Thongpanchang, T. Krauss, L. Brus, J. Am. Chem. Soc.,1999, 121, 3453-3459
4. E. M. Maya, A. W. Snow, J. S. Shirk, R. G. S. Pong, S. R. Flom, G. L. Roberts, J. Mater. Chem., 2003, 13, 1603-1613
5. G. de la Torre, P. Vazquez, F. Agullo-Lopez and T. Torres, J. Mater. Chem., 1998, 8, 1671-1683.
6. J. Britton, M. Durmus ̧ S. Khene, V.Chauke, T. Nyokong, J. Porphyrins Phthalocyanine, 2013, 17, 692-702.
7. C. Mkhize, J. Britton, T. Nyokong, Polyhedron, 2014, 81, 607-613.
8. J. Britton, M. Durmuş, V. Chauke, T. Nyokong, Journal of Molecular Structure, 2013, 1054-1055, 209-214.
9. C. Nitschke, S. M. O’Flaherty, M. Kroll, J. J. Doyle, W. J. Blau, Chemical Physics Letters, 2004, 383, 555-560.