Molecular-Wire Behavior of OLED Materials:  Exciton Dynamics in Multichromophoric Alq3-Oligofluorene-Pt(II)porphyrin Triads

Victor A. Montes,† César Pérez-Bolívar,† Neeraj Agarwal,† Joseph Shinar,‡ and Pavel Anzenbacher, Jr.*†
Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, and Ames Laboratory-USDOE and Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011
J. Am. Chem. Soc., 2006, 128 (38), pp 12436–12438
DOI: 10.1021/ja064471i
Publication Date (Web): August 31, 2006
Copyright © 2006 American Chemical Society
†

 Bowling Green State University.

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‡

 Iowa State University.

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*

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

, pavel@bgnet.bgsu.edu

Abstract

Abstract Image

Donor-bridge-acceptor triads consisting of the Alq3 complex, oligofluorene bridge, and PtII tetraphenylporphyrin (PtTPP) were synthesized. The triads were designed to study the energy level/distance-dependence in energy transfer both in a solution and in solid state. The materials show effective singlet transfer from the Alq3-fluorene fluorophore to the porphyrin, while the triplet energy transfer, owing to the shorter delocalization of triplet excitons, appears to take place via a triplet energy cascade. Using femtosecond transient spectroscopy, the rate of the singlet−singlet energy transfer was determined. The exponential dependence of the donor−acceptor distance and the respective energy transfer rates of 7.1 × 1010 to 1.0 × 109 s-1 with the attenuation factor â of 0.21 ± 0.02 Å-1 suggest that the energy transfer proceeds via a mixed incohererent wire/superexchange mechanism. In the OLEDs fabricated using the Alq3-oligofluorene-PtTPP triads with better triplet level alignment, the order of a magnitude increase in efficacy appears to be due to facile triplet energy transfer. The devices, where the triplet−triplet energy transfer is of paramount importance, showed high color purity emission (CIE X,Y:  0.706, 0.277), which is almost identical to the emission from thin films. Most importantly, we believe that the design principles demonstrated above are general and may be used to prepare OLED materials with enhanced quantum efficacy at lowered operational potentials, being crucial for improved lifespan of OLEDs.

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History

  • Published In Issue September 27, 2006
  • Received July 7, 2006

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