Search

The design of advanced optical materials based on triplet states requires knowledge of the triplet energies of the molecular building blocks. To this end, we report the triplet energy of cyanostar ( CS ) macrocycles, which are the key structure-directing units of small-molecule ionic isolation lattices (SMILES) that have emerged as programmable optical materials. Cyanostar is a cyclic pentamer of covalently linked cyanostilbene units that form π-stacked dimers when binding anions as 2:1 complexes. The triplet energies, E T , of the parent cyanostar and its 2:1 complex around PF 6 - are measured to be 1.96 and 2.02 eV, respectively, using phosphorescence quenching studies at room temperature. The similarity of these triplet energies suggests that anion complexation leaves the triplet energy relatively unchanged. Similar energies (2.0 and 1.98 eV, respectively) were also obtained from phosphorescence spectra of the iodinated form, I-CS , and of complexes formed with PF 6 - and IO 4 - recorded at 85 K in an organic glass. Thus, measures of the triplet energies likely reflect geometries close to those of the ground state either directly by triplet energy transfer to the ground state or indirectly by using frozen media to inhibit relaxation. Density functional theory (DFT) and time-dependent DFT were undertaken on a cyanostar analogue, CSH , to examine the triplet state. The triplet excitation localizes on a single olefin whether in the single cyanostar or its π-stacked dimer. Restriction of the geometrical changes by forming either a dimer of macrocycles, ( CSH ) 2 , or a complex, ( CSH ) 2 ·PF 6 - , reduces the relaxation resulting in an adiabatic energy of the triplet state of 2.0 eV. This structural constraint is also expected for solid-state SMILES materials. The obtained T 1 energy of 2.0 eV is a key guide line for the design of SMILES materials for the manipulation of triplet excitons by triplet state engineering in the future.

Functionalization of new sites on the triangulenium structure has been achieved by early-stage chlorination with N -chlorosuccinimide (NCS), giving rise to two new triangulenium dyes ( 1 and 3 ). By introducing the chlorine functionalities in the acridinium precursor, positions complementary to those previously obtained by electrophilic aromatic substitution on the final dyes are accessed. The chlorination is selective, giving only one regioisomer for both mono- and dichlorination products. For the monochlorinated acridinium compound, a highly selective ring-closing reaction was discovered, generating a single regioisomer of the cationic [4]helicene product. Further investigations into the mechanism of the [4]helicene formation lead to the first isolation of the previously proposed intermediate of the two-step S N Ar reaction, key to all aza-bridged triangulenium and helicenium systems. Late-stage functionalization of DAOTA + with NCS gave rise to a different dichlorinated compound ( 2 ). The fully ring closed chlorinated triangulenium dyes 1 , 2 , and 3 show a redshift in absorption and emission, while maintaining relatively high fluorescence quantum yields of 36%, 26%, and 41% and long fluorescence lifetimes of 15, 12.5, and 16 ns, respectively. Cyclic voltammetry shows that chlorination of the triangulenium dyes significantly lowers reduction potentials and thus allows for efficient tuning of redox and photoredox properties.