Exciton Migration and Surface Trapping for a Photonic Crystal Displaying Charge‐Recombination Fluorescence

Abstract

A compact donor-acceptor molecular dyad has been synthesized by attaching an N,N-dimethylamino fragment to a naphthalic anhydride residue. The dyad shows fluorescence from an intramolecular charge-transfer state (i.e., charge-recombination fluorescence) in solution, with the photo-physical properties being strongly dependent on the solvent polarity. Similar emission is seen for single crystals of the target compound, the molecules being aligned head-to-head, although time-resolved emission profiles display dual-exponential kinetics. A second polymorph with the head-to-tail alignment also gives rise to two lifetimes that differ somewhat from those of the first structure, which are assigned to bulk and surface-bound molecules. Growing the crystal in the presence of Rhodamine B localizes the dye around the surface. Excitation of the crystal is followed by sub-ps exciton migration along the aligned stacks, with occasional crossing to adjacent stacks and trapping at the surface. Rhodamine B present at very low levels acts as the acceptor for excitons entering the surface layer. Crystals embedded in a polyester resin form an artificial light-harvesting antenna able to sensitize an amorphous silicon solar cell.

Charge‐Transfer and Arrangement Effects on Delayed Photoluminescence from Phthalimide Cocrystals

“…Melting points were recorded on aY anaco MP-S3 apparatus and reported uncorrected. 1 Ha nd 13 CNMR spectra were recorded on aB ruker-Biospin DRX-500 spectrometer,a nd chemical shifts were referenced to tetramethylsilane. IR spectra were recorded using aJ ASCO FT/IR-4100 Fourier Transform Infrared Spectrometer.…”

“…[8b] Cocrystallization and host-guest inclusion complexation are important techniques used to create new optical materials. [10][11][12][13][14][15] In this regard, substances that form regular columnar matrixes in their crystalline states are potential candidates as long-lived photoluminescence (PL) materials.…”

Solid‐State Emission from Mono‐ and Bichromophoric Boron Dipyrromethene (BODIPY) Derivatives and Comparison with Fluid Solution

“…Direct excitation into the H‐band, where the interface‐facilitated aggregate appears not to absorb, leads to fluorescence from the aggregate. This situation requires electronic energy transfer from the bulk material to molecules within the interfacial domain . There is good spectral overlap between emission from the J‐species and absorption by the aggregate (Figure S40), which should help promote dipole‐dipole electronic energy transfer.…”

“…Photonic crystals obtained from BODIPY‐based substances appear to form an amorphous domain, or deposit, as an interface with the ordered crystalline columns. These relatively disordered regions offer the possibility to assemble different types of intermolecular species with closer interactions than found in the ordered columns.…”

“…This situation requires electronic energy transfer from the bulk materialt om olecules within the interfaciald omain. [51] There is good spectralo verlap between emission from the J-species and absorption by the aggregate (Figure S40), which should help promote dipole-dipole electronic energy transfer.L ikewise, the smallS tokes shift should facilitatef ast Coulombictype exciton migration between pairs of BC2 chromophores occupying columns within the bulk crystal ( Figure S41).…”