Synthesis, Spectral and Electrochemical Studies of Phenothiazine Appended ‟Push-Pull” a3b Porphyrins and Their Utilization in Nonlinear Optics

Abstract

Porphyrins are ubiquitous in nature [1] and playing a vital role in biological and material applications [2]. Particularly, ‘push-pull’ porphyrins are used in solar cells, nonlinear optics (NLO), toxic ion-sensing and catalysis [3]. Herein, we are reporting the facile synthesis of phenothiazine appended A3B porphyrins. The free base porphyrin, 5,10,15-tris(3-(N-ethylphenothiazinyl)-20-(4-nitrophenyl)porphyrin, H2A3B (1) and their metal Zn(II), Cu(II) and Ni(II) complexes were synthesized [4]. The phenothiazine appended A3B porphyrins exhibited red-shifted absorption and emission spectral features. We have also studied the electrochemical properties of all the synthesized porphyrins. ZnA3B (1a) porphyrin has shown cathodic shift for the first oxidation potential and marginal shift in reduction potential as compared to ZnTPP (Figure 1). The calculated ground state dipole moments of were in the range of 9.64-8.59D as compared to MTPPs (0.052-0.0013 D) and hence they are the potential candidates for NLO application. Ultrafast nonlinear optical (NLO) studies revealed strong two-photon absorption coefficients and cross-sections for these molecules. Further, femtosecond transient absorption studies demonstrated several ultrafast processes from various excited states in these push-pull porphyrin, useful for identifying the processes relevant for optical switching applications. Figure 1: Molecular structures of synthesized porphyrins and their comparative UV-visible spectra in CH2Cl2 and Cyclic voltammograms in CH2Cl2 using TBAPF6 as supporting electrolyte at 298 K. Reference Shao, S.; Rajendiran, V.; Lovell, J. F., Chem. Rev., 2017. 379, 99-120.D. R.; Summerville, D. A.; Basolo, F. Chem. Rev. 1979, 79, 139-179.(a) Prakash, K.; Manchanda, S.; Sudhakar, V.; Sharma, N.; Sankar, M.; Krishnamoorthy, K. Dyes Pigm. 2017, 147, 56-66. (b) Yadav, P.; Kumar, R.; Saxena, A.; Butcher, R. J.: Sankar, M. J. Inorg. Chem. 2017, 26, 3269-3274. (c) Kalnoor, B. S.; Bisht, P. B.; Jena, K. C.; Velkannan, V.; Bhyrappa, P. J. Phys. Chem. A. 2013, 117, 8216-8221. (d) Kumar, R.; Sudhakar, V.; Prakash, K.; Krishnamoorthy, K.; Sankar, M. ACS Appl. Energy Mater. 2018, 1, 2793–2801. (e) Rathi, P.; Ekta, Kumar, S.; Banerjee, D.; Soma V. R.; Sankar, M. Dalton Trans. 2020, 49, 3198-3208.(a) Routhmund et al., J. Am. Chem. Soc, 1936, 58, 625-626. (b) Adler et al., Org. Chem., 1967, 34, 476-479. Figure 1