A very rapid electronic relaxation process in a highly conjugated Zn(ii)porphyrin–[26]hexaphyrin–Zn(ii)porphyrin hybrid tape. Issue 4 (8th January 2016)

• Record Type: Journal Article
• Authors: Lee, Sangsu; Mori, Hirotaka; Lee, Taegon; Lim, Manho; Osuka, Atsuhiro; Kim, Dongho
• Is Part Of: Physical chemistry chemical physics. Volume 18:Issue 4(2016)
• Page Start: 3244
• Page End: 3249
• Publication Date: 2016-01-08
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c5cp07417g
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : We demonstrate that the electronic deactivation overtakes the vibrational relaxation processes in the energy relaxation processes from the initially excited vibronic state manifolds in highly conjugated molecular systems. Abstract : The excited-state energy relaxation processes of a Zn(ii )porphyrin–[26]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 [26]hexaphyrin core inHZn . In contrast toHZn, a biexponential decay with the time constants of 0.25 and 6.5 ps was observed in the decay profile ofFZn . The detailed analysis of excitation wavelength, temperature and solvent dependent TA inFZn 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 conjugatedFZn .