Self-trapping and excited state absorption in fluorene homo-polymer and copolymers with benzothiadiazole and tri-phenylamine

Abstract

Excited state absorption (ESA) is studied using time-dependent density functional theory and compared with experiments performed in dilute solutions. The molecules investigated are a fluorene pentamer, polyfluorene F8, the alternating F8 copolymer with benzothiadiazole F8BT, and two blue-emitting random copolymers F8PFB and F8TFB. Calculated and measured spectra show qualitatively comparable results. The ESA cross-section of co-polymers at its maximum is about three times lower than that of F8. The ESA spectra are found to change little upon structural relaxation of the excited state, or change in the order of sub-units in a co-polymer, for all studied molecules. In all these molecules, the strongest ESA transition is found to arise from the same electronic process, exhibiting a reversal of the charge parity. In addition, F8PFB and F8TFB are found to possess almost identical electronic behaviour.

Excited state absorption spectra of dissolved and aggregated distyrylbenzene: A TD-DFT state and vibronic analysis

“…17 This is partly due to the fact that the respective algorithms (based on quadratic response (QR) functions) have been developed merely within a limited number of quantum-chemical methodologies, and have been implemented only in a few quantum-chemical program packages that require some expert knowledge. For these reasons, the number of computational ESA studies on conjugated molecules is quite limited, 18,19 while the application of QR towards the calculation of two-photon absorption (TPA) is more frequently found in the literature. [20][21][22] Furthermore, didactic approaches to understand the constituting factors of the excitations are rather missing; methodology tests are scarce, and more advanced studies, i.e., on vibronic coupling in ESA spectra or the treatment of molecular assemblies have not been carried out until now.…”

Thickness Dependence of Electronic Structure and Optical Properties of F8BT Thin Films

“…The spectra are normalized to the absorbance value at 462 nm. This main absorption band in the spectra is caused by π-π* electron transitions of π-delocalized electrons along the polymer chain, mainly along the F8 unit [ 29 ]. With increasing thickness, the absorption spectra show a tiny blue shift of maxima less than 10 nm, where the absorbance maximum, for film with thickness 10 nm, is 462 nm; in the case of thicker films, the maximum is at 454 nm.…”

Excited state absorption of DNA bases in the gas phase and in chloroform solution: a comparative quantum mechanical study

“…1,2 This is a quite challenging task due to the large congestion of the excited electronic states in the high energy region and, at the same time, to the ‘interference’ of emission and ground state absorption processes, making the contribution of quantum mechanical calculations crucial. 4–14 In this respect, in a very recent study 15 we considered the two lowest-energy excited states of uracil and benchmarked the ESA spectra computed by TD-DFT and the widely used CAM-B3LYP functional, 16 with those provided by some accurate wavefunction-based methods, namely equation of motion coupled cluster singles and doubles (EOM-CCSD), 17 singles, doubles and perturbative triples (EOM-CC3) 18 and three methods of the Algebraic Diagrammatic Construction family, namely ADC(2), ADC(2)-x and ADC(3). 19 Our investigation was presented shortly after a comprehensive study of the ESA from ππ* of DNA bases at the RASPT2 level by Jaiswal et al 13…”