The excited-state energy relaxation processes of a Zn(ii)porphyrin-hexaphyrin-Zn(ii)porphyrin triply linked hybrid tape, FZn, have been investigated by femtosecond transient absorption spectroscopy (TA), using a directly meso-meso linked hybrid trimer, HZn, as a reference compound. FZn has a very small S1-S0 energy gap through the expansion of π-conjugation and the absorption band at 1897 nm corresponds to its lowest singlet excited-state as a consequence of enhanced transition dipole moment that lies parallel to the long molecular axis. In TA measurements, we observe an energy transfer process (0.4 ps) from the Zn(ii)porphyrin moiety to the hexaphyrin core in HZn. In contrast to HZn, a biexponential decay with the time constants of 0.25 and 6.5 ps was observed in the decay profile of FZn. The detailed analysis of excitation wavelength, temperature and solvent dependent TA in FZn revealed that the electronic relaxation process (0.25 ps) from S1 to S0 is faster than the vibrational relaxation processes (5.9 ps) in the excited and ground states due to a very small S1-S0 energy gap through the expansion of π-conjugation. Accordingly, we demonstrate that electronic deactivation overtakes vibrational relaxation processes in a highly conjugated FZn.
Bibliographical noteFunding Information:
The work at the Yonsei University was supported by the Global Research Laboratory (2013K1A1A2A02050183) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT (Information and Communication Technologies) and Future Planning, and an AFSOR/AOARD grant (FA2386–12–1–4057). The work at Kyoto was supported by JSPS KAKENHI Grant No. 25220802 and 25620031. H. M. acknowledges JSPS Fellowship for Young Scientists. The work at the Pusan National University was supported by the National Research Foundation of Korea (NRF) grants funded by the Korea government (MEST) (NRF-2014R1A2A2A01002456, NRF-2014R1A4A1001690).
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All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry