Exploring excited-state decay pathways in organic chromophore assemblies often requires significant synthetic effort to systematically change interchromophore distances. Moreover, the solubility of these assemblies is often limited. Herein, we examine how nanoporous anodic aluminum oxide (AAO) membranes can address both of these issues by covalently attaching 3-(phenylethynyl)perylene (PEP) and 1,6,7,12-tetrakis(4-tert-butylphenoxy)perylene(3,4:9,10)-bis(dicarboximide) (tpPDI) chromophores with different loadings to AAO membranes, where the estimated average distance between chromophores on the AAO membranes for PEP-AAO-1, -2, and -3 is 5, 8, and 16 Å, respectively, while that between tpPDI cores in tpPDI-AAO-1, -2, -3, and -4 is 4, 6, 10, and 17 Å, respectively. When PEP-AAO-1, -2, and -3 are photoexcited, we observe a distribution of excimer-like states with varying degrees of charge-transfer (CT) character depending on the interchromophore spacing and solvent polarity. Increasing solvent polarity or decreasing the interchromophore distance increases the CT character in the excimer state. Notably, a PEP excimer state having significant CT character still forms in air, that is, in the absence of solvent. In contrast, when tpPDI-AAO-1 is photoexcited in solvents of varying polarity, as well as in air, we observe full symmetry-breaking charge separation (SB-CS) between tpPDIs attached to the AAO membrane. The SB-CS and charge recombination rates increase with increasing solvent polarity as the energy of the CT state is lowered. As the average distance between the tpPDIs increases in the series tpPDI-AAO-1, -2, -3, and -4, the SB-CS rate decreases with no SB-CS observed in tpPDI-AAO-4. This demonstrates the utility of AAO membranes to control the fate of electronic excited states by tuning the various contributions from Coulombic and charge transfer coupling.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films