Understanding the origin and sensitivity of carbon dot emission will improve their utility in various applications.

π-stacked organic electronic materials are tunable light absorbers with many potential applications in optoelectronics. The optical properties of such molecules are highly dependent on the nature and energy of electron–hole pairs or excitons formed upon light absorption, which in turn are determined by intra- and intermolecular electronic and vibrational excitations. Here, we present a first-principles approach for describing the optical spectrum of stacked organic molecules with strong vibronic coupling. For stacked perylene tetracarboxylic acid diimides, we describe optical excitations by using the time-dependent density functional theory with a Franck–Condon Herzberg–Teller approximation of vibronic effects and validate our approach with comparison to experimental ultraviolet–visible (UV–vis) absorption measurements of solvated model systems. We determine that for larger macromolecules, unlike for single molecules, the sampling of the ground-state potential energy surface significantly influences the optical absorption spectrum. We account for this effect by applying our analysis to ∼100 structures extracted from equilibrated molecular dynamics simulations and averaging the optical spectrum over the entire ensemble. Additionally, we demonstrate that intermolecular electronic coupling within the stacks results in multiple low-energy electronically excited states that all contribute to the optical spectrum. This study provides a computationally feasible recipe for describing the spectroscopic properties of stacked organic chromophores via first-principles density functional theory.

Chemical functionalization-introduced sp 3 quantum defects in single-walled carbon nanotubes (SWCNTs) have shown compelling optical properties for their potential applications in quantum information science and bioimaging. Here, we utilize temperature-and power-dependent electron spin resonance measurements to study the fundamental spin properties of SWCNTs functionalized with well-controlled densities of sp 3 quantum defects. Signatures of isolated spins that are highly localized at the sp 3 defect sites are observed, which we further confirm with density functional theory calculations. Applying temperature-dependent line width analysis and power-saturation measurements, we estimate the spin−lattice relaxation time T 1 and spin dephasing time T 2 to be around 9 μs and 40 ns, respectively. These findings of the localized spin states that are associated with the sp 3 quantum defects not only deepen our understanding of the molecular structures of the quantum defects but could also have strong implications for their applications in quantum information science.

Single-walled carbon nanotubes (SWCNTs) containing sp3 defects are a promising class of optoelectronic materials with bright photoluminescence and demonstrated single-photon emission. Using density functional theory simulations, complemented by measurements, we investigate the electronic structure of a series of quantum defects attached to (6,5) SWCNT with the goal of tuning the spin–orbit coupling by introduction of a heavy atom in the defect structure. We characterize the ground state electronic and spin properties of four synthesized and three potential defects on the tube and find that all of the synthesized defects considered introduce a localized midgap defect-centered state containing a single electron, ≈0.2–0.3 eV above the valence band. The spin density is located at the sp3 defect site with negligible spin–orbit coupling even with the presence of a Pd atom. Three additional functional groups were tested via computation to increase spin localization near the metal, thereby increasing spin–orbit coupling. We predict that only the chlorodiphosphanepalladium(II)– [Cl(PH3)2Pd(II)–] defect results in increased spin–orbit splitting of the defect state and the conduction band associated with the pristine-like SWCNT, a measure of the spin–orbit coupling of excited state transitions. This study suggests that for unpassivated sp3 defects in (6,5) SWCNT, forming a direct bond between a heavy atom and the sp3 carbon allows for tuning of spin–orbit coupling.

Metallophilic interactions, weak interactions between closed-shell metal atoms, have been recently utilized to create unique nanostructures with anisotropy of electronic properties along the direction of the interaction. The strength of the metallophilic interaction is an important factor for the design of these nanostructures. Recently, Doerrer and co-workers presented a general metathesis route to create extended chains of metallophilic double salts with two modular opposite-charge ions with Au­(I) and Pt­(II) centers without bridging ligands. Here, we apply theoretical and experimental angle-resolved Raman spectroscopy to identify the vibrational signature associated with the Au­(I)–Pt­(II) interaction in the double salt wire, [Pt­(terpy)­Cl]­[Au­(CN)2)]. Our study reveals six Raman-active low-energy phonon modes below 75 cm–1 that are anisotropic, as shown by their polarization dependence. By analysis of the low-energy Raman spectrum and the nature of the associated phonon modes, we identify one mode to be associated with the intrachain Pt–Au interactions with a frequency of 57 cm–1. We show that the polarization dependence of the Raman spectrum is the key to elucidating directional metallophilic modes.