Vibronic Spectra of Mixed Frenkel and Charge-Transfer Excitons

• Main Authors: Lalov, I J, Zhelyazkov, I
• Format: Conference Proceeding
• Language: English
• ISSN: 0094-243X
• DOI: 10.1063/1.2733042

The excitonic and vibronic spectra of a molecular chain and of crystal of MePTCDI are studied in the case when: (i) a Frenkel exciton (FE) and charge transfer excitons (CTEs) mix strongly; (ii) two mechanisms of coupling between these mixed excitons and intramolecular vibrations, notably linear and quadratic coupling, are acting. Using a convenient canonical transformation and the Green function method, we calculate the linear optical susceptibility. The spectra of linear absorption in the excitonic and vibronic regions have been calculated introducing the exciton parameters of MePTCDI. These spectra exhibit: (i) a relative separation of vibronics of FE and CTEs and transfer of intensity from a FE to CTEs excitonic and vibronic lines; (ii) a stronger impact of the linear coupling on the intensity of the excitonic and vibronic spectra; (iii) the appearance of a spectral doublet of vibronics of the CTEs-its splitting depends on the parameters of linear and quadratic exciton-phonon coupling in the neutral excited molecule and ions. Moreover, in the case of weak linear exciton-phonon coupling the vibronic line of FE, being wide and flat, lies in two-particle continuum while in the case of intermediate and strong linear coupling the linear absorption is dominated by the bound exciton-phonon states and their narrow Lorentzian maxima depend strongly on the quadratic coupling.