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We investigated rapid energy transfer (ET) processes in dendrimers having meta -linked branching light harvesting antennas. It was found that, at room temperature (RT), the rapid ET occurs efficiently from the antennas to the core and gives rise to intense core-PL bands under the selective excitation on the antenna. However, the ET efficiency impairs at lower temperatures than ∼100 K. For understanding these experimental results, we analyzed molecular vibrations and molecular orbitals (MOs) of a simple model molecule. From these analyses, it was demonstrated that, at RT, the torsional vibration of the entire antenna subunit is excited sufficiently and the torsional vibration improves the co-planarity between the core and the antenna subunit, consequently, the rapid ET is realized by the short-range interaction between the π*-MOs of the core and the antenna. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

From analyses of molecular vibrations, we have studied rapid energy transfer (ET) process in a series of star-shaped stilbenoid phthalocyanines (SSSnPc;n=1,2) having π-conjugated light harvesting antennas. In SSSnPc, the highly efficient ET occurs through a π-conjugation network between the core and the antenna. However, a different temperature dependency of the ET efficiencies were found between SSS1Pc and SSS2Pc. In this report, molecular structures and torsional vibrations of the antenna subunits were analyzed in model molecules for SSSnPc. Consequently, it was found that the co-planarities between the core and the antenna sub-unit are different between SSS1Pc and SSS2Pc, and the variance in the temperature dependence of the ET efficiency in these dendrimers is originated from such difference of the co-planarity (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigate a rapid energy transfer (ET) process and its temperature dependence in a star-shaped stilbenoid phthalocyanine (SSS1Pc) dendrimer having π -conjugated light-harvesting (LH) antennas. In SSS1Pc, intense core-photoluminescence is observed under selective excitation on the LH-antenna as a result of the highly efficient ET from the LH-antenna. Pump-probe experiments show that ET occurs rapidly with a rising time constant (∼ 250 fs). To understand such rapid ET, we employ a simplified ET model through a π -conjugated network between the Lhantenna and the core that takes into account the steric hindrance between the LH-antenna subunits. Our model reveals that the highly efficient ET at room temperature in SSS1Pc takes place through the π -conjugated network mediated by a thermally activated torsional vibration of the aromatic ring subgroup in the LH-antenna. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigate rapid energy transfer (ET) and its temperature dependence in a star-shaped stilbenoid phthalocyanine (SSS1Pc) dendrimer having π-conjugated light-harvesting (LH) antennas, and develop an appropriate model. In SSS1Pc, an intense core photoluminescence (PL) band appears under the selective excitation of the absorption bands of the LH antenna due to highly efficient ET at room temperature (RT). The transient response of core-absorption bleaching and the temporal behaviours of the PL intensities of the core and antenna reveal that ET from the LH antenna occurs rapidly prior to achieving quasi-equilibrium in the photoexcited state of the LH antenna. In addition, it is also clarified that the ET quantum efficiency in SSS1Pc degrades at temperatures lower than ~100 K. To understand these results, we develop an ET model based on a π-conjugating network between the LH antenna and the core that accounts for steric hindrance between the LH antenna and the torsional vibration of the LH-antenna subunit. This model reveals that highly efficient ET occurs at RT through the π-conjugated network mediated by the thermally activated torsional vibration of the LH-antenna subunit.