INTERCALATION OF AMINOPHENYL-SUBSTITUTED AND PYRIDINIUM-SUBSTITUTED PORPHYRINS INTO ZIRCONIUM HYDROGEN PHOSPHATE - EVIDENCE FOR SUBSTITUENT-DERIVED ORIENTATIONAL SELECTIVITY

Aminophenyl- and pyridinium-substituted porphyrins were intercalated i nto the alpha phase of zirconium hydrogen phosphate (alpha-ZrP) by exc hanging the porphyrins into the p-methoxyaniline (PMA) preintercalated compound Zr(O3POH)2.2PMA (alpha-ZrP.2PMA). Porphyrin exchange reactio ns with alpha-ZrP and its ethanol intercalate were unsuccessful. Powde r X-ray diffraction patterns of p-H2TAPP- and H2TMPyP-exchanged alpha- ZrP.2PMA revealed complete conversion of the starting material to phas es with interlayer spacings near 17 angstrom, corresponding to a guest layer thickness of ca. 11 angstrom. The p-H2TAPP derivative was found to partially convert over several weeks to alpha-ZrP and a 24-angstro m phase material. The large interlayer spacing cannot be accounted for by a porphyrin monolayer and is tentatively assigned to a porphyrin b ilayer in which the heme planes are tilted relative to the host lamell ae. Conversely, intercalation of alpha-ZrP-2PMA with the a,a,a,a, a,al pha,a,beta and alpha,beta,alpha,beta atropisomers of o-H2TAPP afforded multiphasic products with interlayer spacings of 13, 17, 19-20, and 2 5 angstrom. The relative intensities of the phases were highly depende nt on the atropisomer, with the alpha,alpha,alpha,alpha isomer forming mainly a 19-angstrom phase and o-alpha,beta,alpha,beta-H2TAPP forming predominantly a 17-angstrom phase. In order to determine the orientat ions of porphyrins comprising the 17- and 19-20-angstrom phases relati ve to the host lamellae,p-CuTAPP and o-alpha,alpha,alpha,alpha-CuTAPP intercalation complexes were prepared, and anisotropic EPR spectra of uniaxially ordered thin films oriented at 0 and 90-degrees relative to the applied magnetic field were recorded. The EPR spectra of the p-Cu TAPP-exchanged host displayed little orientational dependence, consist ent with tilting of the heme macrocycles near 45-degrees relative to t he host lamellae. Conversely, the EPR spectra of uniaxially ordered fi lms of the o-alpha,alpha,alpha,alpha-CuTAPP-exchanged host exhibited a strong orientation dependence, with the perpendicular component of th e Cu(II) signal dominating the spectrum in samples oriented at 90-degr ees relative to B0 and the parallel component predominating in films o riented at 0-degrees relative to B0, indicating that the porphyrins we re highly oriented parallel to the host layers. Together, the XRD and EPR data suggest that the guest morphology of the p-TAPP derivatives c onsisted of a monomolecular porphyrin layer in which the heme planes w ere tilted nearly 45-degrees relative to the host lamellae, whereas o- alpha,alpha,alpha,alpha-TAPP derivatives predominantly assembled into a porphyrin bilayer in which the heme macrocycles lay parallel with th e host sheets. The preferred porphyrin orientations are discussed in t erms of maximization of electrostatic and hydrogen-bonding interaction s between the host and guest.