Rational design of long-wavelength absorbing and emitting carbostyrils aided by time-dependent density functional calculations

Abstract

We have used computational chemistry methods to aid the rational design of long-wavelength absorbing and emitting organic materials. For this purpose, the vertical electronic transition energies of 3,4-dicyano carbostyrils (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 (DMSO, CH3CN, H2O) were taken into account by the CPCM solvation model. Particular long-wavelength absorptions (∼540nm) are predicted for derivatives containing an amino group in position 6 irrespective of whether a 7-methoxy or a 7-amino group is present. In contrast, considerably shorter wavelength absorption (∼440nm) can be expected for 6-methoxy-7-amino substituted 3,4-dicyano 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 accompanied by an extremely low electronic transition energy (1000–1500nm) with vanishingly small intensity (oscillator strength f<0.000). 6-methoxy-7-amino substituted carbostyrils are predicted to emit at 490–520nm. An especially long-wavelength fluorescence (∼660nm) is calculated for 6-amino-7-methoxy- as well as 6,7-bis(methylamino)-3,4-dicyanocarbostyril.