Measurement of the Triplet-Triplet Absorption Spectrum of Tetracene Using cw Argon Laser Excitation

• Published in: The Journal of chemical physics 1972-01, Vol.56 (1), p.227-232
• Main Author: Pavlopoulos, T. G.
• Format: Article
• Language: English
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.1676851

Polarization data for the triplet-triplet (T-T) absorption spectrum of tetracene over the region 310–490 nm were obtained. This spectral range includes the region where strong overlap with singlet-singlet (S-S) absorption occurs. An approximate method was developed to obtain the degree of polarization P of triplet levels in regions of strong S-S absorption. For excitation, the 476.5-nm line from a continuous wave (cw) argon laser was employed. The polarization curve indicates the presence of two different electronic transitions. The three strong absorption bands at 485, 468, and 440 nm are negatively polarized and could be assigned to the B3g-3←B2u+3 transition. The weaker bands at 412, 385, 360, and 320 nm are positively polarized and are thus assigned to the A1g-3←B2u+3 transition. These new data provide a better test of the validity of theoretical predictions on the triplet energy levels of tetracene by Pariser and Orloff than was previously possible without polarization measurements. A correlation diagram is given, which compares the observed and calculated triplet energy levels for naphthalene, anthracene, tetracene, and pentacene. While Orloff's predictions of the intensities of the T-T absorptions agree well with experiment, his energy values are not in good agreement for the high-energy triplet states. Pariser's energy predictions are in better agreement with experimental results than Orloff's, however, his intensity predictions are not in good agreement with experimental data.