The influence of planarity, rigidity and internal heavy atom upon fluorescence parameters and the intersystem crossing rate constant in molecules with the biphenyl basis

Impact of non-symmetric 2,9,10-aryl substitution on charge transport and optical properties of anthracene derivatives

“…The energy of the first triplet state is in range of 1.7-1.77 eV for all 2,9,10-arylanthracene derivatives, similarly as it was observed for similar various anthracene compounds [9,46]. It is known that S 1 -T 1 transition is symmetrically forbidden in anthracene derivatives symmetrically substituted at 9 th and 10 th positions [24] and the intersystem crossing rate is almost suppressed [25] if there is no higher triplet levels below the S 1 . ISC notably increases when higher triplet levels with appropriate symmetry emerges below the S 1 state energy and causes the remarkable decrease in the fluorescence efficiency [24,25].…”

“…It is known that S 1 -T 1 transition is symmetrically forbidden in anthracene derivatives symmetrically substituted at 9 th and 10 th positions [24] and the intersystem crossing rate is almost suppressed [25] if there is no higher triplet levels below the S 1 . ISC notably increases when higher triplet levels with appropriate symmetry emerges below the S 1 state energy and causes the remarkable decrease in the fluorescence efficiency [24,25]. In our case, the T 2 state was observed at about 2.72 eV with minor changes of energy.…”

“…Substitution at the 9 th and 10 th position with phenyl groups (or other aryl groups [22-24]) remarkably decreases ISC rate and enhances fluorescence quantum yield up to the unity [24,25].…”

“…While introduction of more bulky substituents reduces the nonradiative decay constant from 7.0 ns to 6.52 ns in solution, for compounds 2a and 5b, respectively. Thus more realistic route of nonradiative deactivation is mechanism of intersystem crossing, which rate is tuned by alignment of S 1 and T n (most likely of T 2 or T 3 ) energy levels[23,24,26,46]. The introduction of 2-phenyl moiety results in proper S 1 and T n level alignment (see Section 2.2) when effective relaxation through triplet states occur what is evidenced reduced τ nr values of compounds 1-6a and 1-6b.…”

Organic Photodiodes: The Future of Full Color Detection and Image Sensing

“…In general, molecules that have narrow spectral band widths possess excited states whose geometries are similar to the ground state (i.e., with very few vibrational levels superimposed on the electronic absorption bands of the molecule -both in the ground and excited states), [ 214 ] and this usually requires the chromophores to have a certain level of rigidity and planarity -resulting in absorption and fl uorescence spectra with well-resolved vibronic bands. [ 215 ] Since higher effi ciencies (and therefore sensitivities) can be obtained through the use of donor-acceptor blends, [ 91 ] the absorption properties of both the donor and acceptor materials need to be considered. The following section will outline and discuss the range of donor and acceptor combinations that have been studied for blue, green and red absorbing layers based on small molecules, dendrimers, and polymers.…”