HIGH-RESOLUTION OPTICAL-SPECTRA FROM ULTRATHIN QUATERTHIOPHENE FILMS

The linear optical properties of quaterthiophene (4T) films of about 2 5 ti thickness were studied, The films were fabricated by vapour depos ition of 4T on highly oriented pyrolytic graphite under high vacuum. I n the photoluminescence and reflection spectra the vibronic lines are very sharp (FWHM (0-0) less than or equal to 50 cm(-1)) indicating a h igh degree of structural order in the films. This is supported by the absence of thermal quenching of the luminescence. Comparison with spec tra of matrix-isolated 4T reveals very similar vibrational energies, i ndicating an undistorted structural conformation of 4T in the film, bu t some additional modes, probably ring deformation modes, are found. I n the reflection spectra a splitting of 170 cm(-1) is observed for the first excited electronic level which is tentatively interpreted as Da vydov splitting.