Affiliation:
1. Department of Chemistry, University of North Texas, 1155 Union Circle, #305070, Denton, TX 76203-5017, USA
2. Department of Physical Sciences and Mathematics Wayne State College, 1111 Main Street, Wayne, Nebraska, 68787, USA
Abstract
Self-assembled donor–acceptor conjugates featuring zinc phthalocyanine carrying four entities of peripheral phenothiazine entities, (PTZ)[Formula: see text]ZnPc, axially coordinated to either phenyl imidazole or pyridine functionalized fulleropyrrolidine (C[Formula: see text]Im or C[Formula: see text]Py) has been newly designed, synthesized and characterized. Due to the direct connectivity of the phenothiazine entities to the ZnPc [Formula: see text]-system, efficient charge transfer type interactions suppressing fluorescence of ZnPc in (PTZ)[Formula: see text]ZnPc was observed. Axial coordination of C[Formula: see text]Im or C[Formula: see text]Py to the metal center of (PTZ)[Formula: see text]ZnPc served as an electron acceptor in the conjugates. Optical absorption studies revealed stable complex formation wherein the evaluated binding constants [Formula: see text] were found to be 3.9 × 10[Formula: see text] M[Formula: see text] for (PTZ)[Formula: see text]ZnPc:ImC[Formula: see text] and 3.3 × 10[Formula: see text] M[Formula: see text] for (PTZ)[Formula: see text]ZnPc:PyC[Formula: see text] conjugates with 1:1 molecular stoichiometry. Computational studies performed at the HF/[6-311G(d,p) for H, C, and N, and 6-311G(2df) for S and Zn] level revealed stable structures of the conjugates. The evaluated center-to-center and edge-to-edge distances for the (PTZ)[Formula: see text]ZnPc:ImC[Formula: see text] were 13.6 and 10.4 Å, while for the (PTZ)[Formula: see text]ZnPc:PyC[Formula: see text] conjugate these distances were 10.2 and 7.3 Å. That is, the C[Formula: see text] was about 3̃ Å closer to ZnPc in the latter conjugate. From the free-energy calculations, photoinduced electron transfer from the [Formula: see text]ZnPc* to fullerene within the conjugates was established to be an exothermic process, however, a hole transfer from ZnPc[Formula: see text] to peripheral PTZ was found to be energetically an uphill process. From femtosecond transient absorbance studies, occurrence of photoinduced charge separation in (PTZ)[Formula: see text]ZnPc:ImC[Formula: see text] was found to be weak due to the competing charge transfer interactions within the (PTZ)[Formula: see text]ZnPc and longer donor–acceptor distance while in the case of the (PTZ)[Formula: see text]ZnPc:PyC[Formula: see text] conjugate, electron transfer occurred competitively to yield radical ion-pairs. From nanosecond transient spectroscopy, lifetime of the (PTZ)[Formula: see text]ZnPc[Formula: see text]:PyC[Formula: see text] charge separated state was found to be in the 200 ns range, revealing charge stabilization to some extent.
Publisher
World Scientific Pub Co Pte Lt
Cited by
10 articles.
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