Spectroscopy of BODIPY in solid phase: crystal and nanoparticles

Abstract

We compare the absorption and fluorescence spectra of single crystals and suspensions of nanoparticles with the prediction of the Frenkel theory. The single crystals of a novel synthesized fluorescent BODIPY derivative dye, adamantyl mesityl BODIPY (4,4-difluoro-3,5-di-(adamantyl)-8-mesityl-4-bora-3a,4a-diaza-s-indacene), have been prepared. Their birefringence and dichroism have been studied. The X-ray crystallography shows a monoclinic crystal with all transition moments parallel to one common plane. The refractive indices along the two neutral axes have been measured for a wavelength from 530 to 700 nm, with a difference, Δn equal to 0.11. The Frenkel exciton theory was used here to describe the coupling of the electronic excited states in the crystals. The coupling estimated by the dipolar approximation was compared with the excited state splitting calculated by TDDFT in dimers. A perfect crystal absorption spectrum is predicted. The spectral broadening that occurs at room temperature is also taken into account. The absorption spectrum of the monocrystal is reproduced without adjustable parameters. But we had to take into account the presence of optical leaks in our microspectrophotometer before comparing experiment and theory. The controlled size nanoparticles (NPs) produced by our 3D hydrodynamic focusing microfluidic system exhibit molecule like absorption. We could reproduce their absorption and fluorescence spectra assuming a strong disorder in the Frenkel model. We conclude that the nanoparticles are amorphous.

Intermolecular states in organic dye dispersions: excimers vs. aggregates

“…S2, ESI †). 9,10,[12][13][14][15][16][17][18][19][20][21] However, in both film types this quenching saturates for high loading at remarkably high efficiencies (40.10) for a concentrated BODIPY film.…”

“…In the case of BODIPY dyes, it has been well documented in a wide range of derivatives that dispersion within a polymer matrix or deposition of pure films results in significant PL quenching accompanied by spectral shifts. 9,10,[12][13][14][15][16][17][18][19][20][21] Analogous effects have also been described in a wide range of covalent dimers, 11,15,[21][22][23][24][25][26] though the geometries are typically a poor match for the structures obtained in the solid state. Quenching in these systems is often attributed to the formation of non-emissive H-aggregates, identified by a broadening of the absorption spectrum at higher energies.…”

“…10,[15][16][17]26,27 Red-shifted PL spectral features have been variously attributed to excimers and J-aggregates, typically on the basis of their spectral position alone. 6,9,[12][13][14][19][20][21][22][23][24] The properties of these emissive states have not been analyzed in detail, nor the mechanism of their formation. We have recently demonstrated that the excimer state formed in a high-concentration BODIPY dispersion enables exciton-polariton formation through a novel radiative pumping mechanism, 28 highlighting the potential of these low-energy states for applications if their properties can be better understood.…”

Fluorescence Spectroscopy of AdamBODIPY Single Crystals

“…Lately, several of us have developed BODIPYs with spacers based on paracyclophane and iodophenyl groups . More recently, thin single crystals of adamantyl‐mesityl‐BODIPY (AdamBODIPY) were successfully grown by a precipitation method that some of us reported earlier . AdamBODIPY in the solid state has a shorter fluorescence lifetime and a lower quantum yield (0.9 ns and Φ =0.15) compared to that of the molecule in dichloromethane (5.7 ns and Φ =0.79; see Ref.…”

“…, p. 69 and p. 84). (b) Stereo plot of the unit cell of AdamBODIPY crystal with the view on the plane hkl=(703) defined by the transition moments . The long axis of the crystal is along the b direction of the cell.…”