Spectroscopic and thermodynamic studies of light harvesting perylenediimide derivative - zinc porphyrin complex in aqueous media

Abstract

Self-assembly of perylene derivative such as N,N′-bis(2(trimethylammonium iodide) ethylene)perylene-3,4,9,10-tetracarboxyldiimide (TAIPDI) can produce one-dimensional form (1D) in an aqueous media. The ability of one-dimensional TAIPDI to form light harvesting complex with water-soluble zinc porphyrin (ZnTPPS4) via the π-π and electrostatic interactions has been described. Owing to electronic interactions between the π-systems, the complex formation is accompanied by pronounced absorption spectral changes in the UV/Vis absorption bands. The formation constant of the ZnTPPS4-TAIPDI complex has been determined as 2.60×104M−1 suggests a moderately stable complex. The steady-state fluorescence measurements exhibited fluorescence quenching of both the singlet TAIPDI and ZnTPPS4 because of the electron transfer process from the electron-donating ZnTPPS4 to the electron-accepting TAIPDI. Based on the picosecond time-resolved fluorescence, the rate and quantum yield of the electron transfer were found to be 2.47×1010s−1 and 0.99, respectively, indicating fast and efficient electron transfer. The thermodynamic parameters of the complex formation have been determined from the stopped-flow measurements. The interaction between ZnTPPS4 and TAIPDI occurs in two steps, a fast and reversible step followed by a slow and irreversible one. The activation parameters for the complex formation (ΔH#=22±5kJmol−1 and ΔS#=−123±18JK−1mol−1), (ΔH#=133±4kJmol−1 and ΔS#=167±13Jmol−1K−1) were determined from variable temperature studies for the “on” and the “off” of the first step and ΔS#=246±37.89Jmol−1K−1 and ΔH#=130±11kJmol−1 for the second step. The negative and positive ΔS# values found for the interaction reactions are consistent with an associative interaction for the first step followed by dissociative mechanism for both the “off” and the second step.