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A joint theoretical-experimental study on the optical properties of 5-N-succinimidyl-2.2 -bithiophene (NS-2T), a prototype system for a new class of biomarkers was conducted, and time-dependent density functional theory (TD-DFT) and approximate coupled-cluster single and doubles (CC2) calculations were performed in the ground and excited states. Results showed that CC2 and TD-DFT can very well describe the absorption and photoluminescence energies of the three systems, but the presence of several charge-transfer transitions in the TD-DFT spectrum of NS-2T required the use of a correlated method to validate the TD-DFT results.

Singlet and triplet excitation energies in oligothiophenes are analyzed using time-dependent density-functional theory (TD-DFT) with different exchange-correlation functionals. TD-DFT methods underestimate photoluminescence energies but the energy difference between singlet and triplet states shows a trends with the chain-length similar to coupled-cluster singles and doubles model (CC2).

The intramolecular radiative and nonradiative relaxation processes of three thiophene-S,S-dioxide derivatives with different molecular rigidity are investigated in different solutions and inert matrix. It is shown that the fluorescence quantum efficiency and the relaxation dynamics are strongly dependent on the environment viscosity, whereas they are almost independent of the environment polarity.