Excited-State Relaxation Process of Free-Base and Oxovanadium Naphthalocyanine in Near-Infrared Region

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• 作者：Fuyuki Ito ; Tatsuaki Inoue ; Daisuke Tomita ; Toshihiko Nagamura
• 刊名：Journal of Physical Chemistry B
• 出版年：2009
• 出版时间：April 23, 2009
• 年：2009
• 卷：113
• 期：16
• 页码：5458-5463
• 全文大小：193K
• 年卷期：v.113,no.16(April 23, 2009)
• ISSN：1520-5207

文摘

Excited-state relaxation process of free-base and oxovanadium naphthalocyanine (H₂Nc and VONc) in solutions and in polymer films was studied by transient absorption measurements. In polymer films only H-aggregate was observed with H₂Nc with increasing its weight fraction, whereas VONc formed both H- and J-type aggregates. The transient absorption of singlet excited-state of H₂Nc and VONc in toluene solution decayed with time constant of 250 ± 30 and 12 ± 2 ps, respectively. The relaxation from singlet excited state of H₂Nc and VONc in toluene solution is governed by the IC and ISC, respectively. The central metal ion, VO²⁺, acceralated the ISC by the spin−orbital coupling due to unpaired electron. The excited-state relaxation in polymer films differed from that in toluene solution, which originates from the exciton−exciton annihilation process. The excitation power dependence of the excited-state dynamics and weight ratio dependence of absorption spectrum suggests that the aggregation of VONcs contributes to faster decay from the singlet excited-state. The excition-exciton annihilation occurs more efficiently in VONc system compared with H₂Nc system. The dipole−dipole interaction depending on the aggregated structure controls excited-state relaxation processes in polymer films. This is mainly due to the differences in the transition dipole moment between H- and J-type aggregates. The ultrafast deactivation of VONc in polymer films can be applied to all-optical ultrafast modulation in the optical telecommunication wavelength region.