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Computational Design of Long-Wavelength Absorbing and Emitting Carbostyrils
* 1 , * 2 , 3
1  Institute of Physical and Theoretical Chemistry, Graz University of Technology, Stremayrgasse 9/I, 8010 Graz, Austria
2  Institute of Chemistry, Karl-Franzens-University Graz, Heinrichstr. 28, A-8010 Graz, Austria
3  Institute of Chemistry, University of Graz, Heinrichstraße 28, 8010 Graz, Austria

Abstract: We have used computational chemistry methods to aid the rational design of long-wave length absorbing and emitting organic materials. For this purpose, the vertical electronic transition energies of 3,4-dicyano carbostyriles (quinolone-2(1H)-ones) substituted by electron-donating substituents (methoxy,methylamino, dimethylamino) at positions 6 and 7, are calculated by time-dependent density functional theory (B3LYP) within the Tamm-Dancoff approximation. Bulk solvent effects (CH3CN, DMSO, H2O)were taken into account by the CPCM solvation model. Particular long-wavelength absorption ( ~ 540 nm) is found for derivatives containing an amino group in position 6 irrespective of whether a 7-methoxy or an 7-amino group is present. In contrast, considerably shorter wave length absorption ( ~ 440 nm) results for 6-methoxy-7-amino substituted carbostyrils. Optimization of the first excited singlet state of 6-dimethylamino substituted carbostyrils leads to a perpendicular arrangement of the (CH3)2N – group with respect to the heterocyclic ring system leading to an extremely low electronic transition energy (1000 – 1500 nm) with vanishingly small intensity (oscillator strength f < 0.000). 6-Methoxy-7-amino substituted carbostyrils are predicted to emit at 490 – 520 nm. An especially long-wave length fluorescence ( ~ 660 nm) is calculated for 6-amino-7-methoxy- as well as 6,7-bis(methylamino)-3,4-dicyanocarbostyril.
Keywords: Absorption; fluorescence; TDDFT; excitation energies; quinolones; substituent effects