Electronic transitions of some pi-molecular charge transfer complexes. [Anthracene--pyromellitic dianhydride (PMDA) or pyrene--PMDA in naphthalene--PMDA host]

Thesis/Dissertation · Thu Dec 01 04:00:00 EST 1977

DOI:https://doi.org/10.2172/5343529· OSTI ID:5343529

Beckman, Robert Lee ^[1]

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1. Iowa State Univ., Ames, IA (United States)

A unique phonon progression in the phosphorescence spectrum of pyrene-PMDA (Py-PMDA) in naphthalene-PMDA (N-PMDA) is reported. Calculations of the electron-phonon coupling strength parameter for the ground and excited states indicate strong coupling for the fractional CT contribution of Py-PMDA to the observed phosphorescent state. Model calculations indicate that the observed low frequency phonon mode corresponds to a low energy rotation of the rigid guest complex and not a symmetric donor-acceptor stretch. The unusual reduction of the phonon mode frequency in the excited ground state is explained in terms of a contracted complex that can more easily rotate in a larger cavity. A brief phonon progression is also observed for the mixed crystal A-PMDA in N-PMDA. For both mixed crystals, Py-PMDA in N-PMDA and A-PMDA in N-PMDA, the energy spacing between the zero-phonon vibrational bands in the mixed CT crystal phosphorescence spectrum are very similar to those obtained from the phosphorescence spectrum of the pure donor in a rigid matrix. There is a large blue shift between the origin band of the mixed CT crystal phosphorescence spectrum and the origin band of the pure donor phosphorescence spectrum for the A-PMDA mixed crystal, but not for the Py-PMDA mixed crystal. The structureless CT absorption spectra of Py-PMDA and A-PMDA mixed crystals indicate strong electron-phonon coupling, as does the structureless CT fluorescence spectrum of A-PMDA in N-PMDA. No CT fluorescence was observed that can be conclusively attributed to Py-PMDA. The CT absorption and emission spectra of the neat N-PMDA host reveal no sharp structure, indicating strong-exciton-phonon coupling. The particularly long absorption tail observed for N-PMDA neat crystals supports the contention that N-PMDA may be disordered.

• Research Organization: Ames Lab., Ames, IA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 5343529
• Report Number(s): IS-T--788
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ABSORPTION SPECTRA
ANHYDRIDES
ANTHRACENE
AROMATICS
CHARGE EXCHANGE
COMPLEXES
CONDENSED AROMATICS
ELECTRONIC STRUCTURE
ENERGY-LEVEL TRANSITIONS
HYDROCARBONS
LUMINESCENCE
NAPHTHALENE
ORGANIC COMPOUNDS
PHONONS
PHOSPHORESCENCE
PYRENE
QUASI PARTICLES
SPECTRA