Including both environmental and vibronic effects is important for accurate simulation of optical spectra, but combining these effects remains computationally challenging. We outline two approaches that consider both the explicit atomistic environment and the vibronic transitions. Both phenomena are responsible for spectral shapes in linear spectroscopy and the electronic evolution measured in nonlinear spectroscopy. The first approach utilizes snapshots of chromophore-environment configurations for which chromophore normal modes are determined. We outline various approximations for this static approach that assumes harmonic potentials and ignores dynamic system-environment coupling. The second approach obtains excitation energies for a series of time-correlated snapshots. This dynamic approach relies on the accurate truncation of the cumulant expansion but treats the dynamics of the chromophore and the environment on equal footing. Both approaches show significant potential for making strides toward more accurate optical spectroscopy simulations of complex condensed phase systems. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 72 is April 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The surface-enhanced Raman scattering (SERS) spectrum of pyridine adsorbed on Ag20 cluster (pyridine-Ag20 ) at room temperature is calculated by performing ab initio molecular dynamics simulations in connection with a Fourier transform of the polarizability autocorrelation function to investigate the static chemical enhancement behind the SERS spectrum. The five enhanced vibrational modes of pyridine, namely, υ6a, υ1, υ12, υ9a, and υ8a, can be assigned and identified by using a new analytical scheme, namely, single-frequency-pass filter, which is based on a Fourier transform filtering technique. To understand the factors evoking the enhancement in the SERS spectrum, the dynamic properties of molecular structures and charges for both of the free pyridine and adsorbed pyridine are analyzed. The calculated results indicate that the vibrational amplitudes of adsorbed pyridine are enhanced due to both of the electron transfer from pyridine to Ag20 cluster and the softening of pyridine bond. In addition, the N-Ag stretching within pyridine-Ag20 will couple with these five vibrational modes of pyridine. Consequently, the electron transfer between pyridine and Ag20 cluster induced by different molecular vibrational modes prompts the redistribution of electron density of pyridine. These factors collectively cause the noticeable change in polarizability during molecular vibrations and hence result in the enhancement of Raman peaks.

Antibiotic resistance genes (ARGs) have become emerging environmental contaminants, and the effective on-site detection of ARGs is urgently needed. Herein, we constructed a hairpin-structured magnetic sensor for the analysis of a widespread ARG, tetA, using surface-enhanced Raman scattering (SERS). The SERS sensor was assembled by immobilizing core-satellite structured Fe 3 O 4 @SiO 2 -Au with single-stranded DNA in a folded hairpin structure. The SERS sensor exhibited good sensitivity and specificity for the detection of laboratory-synthesized tetA ssDNA fragments. In addition, this SERS strategy is the first of its kind to be employed for monitoring environmental samples in the field, with a limit of detection reaching as low as 25 copies μL −1 . Univariate and multivariate linear regression equations verify the practicability of the SERS sensor for quantitative tetA determination, showing the prospect for an amplification-free alternative platform for sensitive and reliable on-site detection of ARGs in the environment.

The alignment of energy levels within an OLED device is paramount for high efficiency performance. In this study, the emissive, electron transport, and hole transport layers are consecutively evolved under the constraint of fixed electrode potentials. This materials development strategy takes into consideration the full multilayer OLED device, rather than just individual components. In addition to introducing this protocol, an evolutionary method, a genetic algorithm (GA), is evaluated in detail to increase its efficiency in searching through a library of 30 million organic compounds. On the basis of the optimization of the variety of GA parameters and selection methods, an exponential ranking selection protocol with a high mutation rate is found to be the preferred method for quickly identifying the top-performing molecules within the large chemical space. This search through OLED materials space shows that the pyridine-based central core with acridine-based fragments are good target host molecules for common electrode materials. Additionally, weak electron-donating groups, such as naphthalene- and xylene-based fragments, appear often in the optimal electron-transport layer materials. Triphenylamine- and acridine-based fragments, due to their strong electron-donating character, were found to be good candidates for the hole-transport layer.