We report the synthesis and basic photophysical characterization of strongly conjugated hydroporphyrin (chlorin and bacteriochlorin) dyads. Hydroporphyrins are connected at their respective 13 (β) or 15 (meso) positions by ethynyl or butadiynyl linkers. Synthesis entails a series of palladium-catalyzed reactions, starting from appropriate bromobacteriochlorin or bromochlorin. Strong conjugation in the dyads results in a significant bathochromic shift of longest-wavelength (Qy-like) band, which in case of the 13-13' ethynyl-linked bacteriochlorin dyad is positioned past 800 nm. The Qy-like band is broad and split for the 13-13' linked chlorin and bacteriochlorin dyads. All dyads exhibit an intense, relatively narrow fluorescence emission band in nonpolar solvents. Bacteriochlorin dyads exhibit a strong dependence of fluorescence intensity on the solvent polarity, which results in more than 10-fold quenching of fluorescence in dimethylformamide. The assembling of hydroporphyrins into strongly conjugated arrays represents an efficient means to tune and expand their optical and photochemical properties, which should greatly broaden the properties attainable for these chromophores.

Achieving tunable, intense near-infrared absorption in molecular architectures with properties suitable for solar light harvesting and biomedical studies is of fundamental interest. Herein, we report the photophysical, redox, and molecular-orbital characteristics of nine hydroporphyrin dyads and associated benchmark monomers that have been designed and synthesized to attain enhanced light harvesting. Each dyad contains two identical hydroporphyrins (chlorin or bacteriochlorin) connected by a linker (ethynyl or butadiynyl) at the macrocycle β-pyrrole (3- or 13-) or meso (15-) positions. The strong electronic communication between constituent chromophores is indicated by the doubling of prominent absorption features, split redox waves, and paired linear combinations of frontier molecular orbitals. Relative to the benchmarks, the chlorin dyads in toluene show substantial bathochromic shifts of the long-wavelength absorption band (17-31 nm), modestly reduced singlet excited-state lifetimes (τS = 3.6-6.2 ns vs 8.8-12.3 ns), and increased fluorescence quantum yields (Φf = 0.37-0.57 vs 0.34-0.39). The bacteriochlorin dyads in toluene show significant bathochromic shifts (25-57 nm) and modestly reduced τS (1.6-3.4 ns vs 3.5-5.3 ns) and Φf (0.09-0.19 vs 0.17-0.21) values. The τS and Φf values for the bacteriochlorin dyads are reduced substantially (up to ∼20-fold) in benzonitrile. The quenching is due primarily to the increased S1 → S0 internal conversion that is likely induced by increased contribution of charge-resonance configurations to the S1 excited state in the polar medium. The fundamental insights gained into the physicochemical properties of the strongly coupled hydroporphyrin dyads may aid their utilization in solar-energy conversion and photomedicine.

Doping of semiconductors enables fine control over the excess charge carriers, and thus the overall electronic properties, crucial to many technologies. Controlled doping in lead-halide perovskite semiconductors has thus far proven to be difficult. However, lower dimensional perovskites such as nanocrystals, with their high surface-area-to-volume ratio, are particularly well-suited for doping via ground-state molecular charge transfer. Here, the tunability of the electronic properties of perovskite nanocrystal arrays is detailed using physically adsorbed molecular dopants. Incorporation of the dopant molecules into electronically coupled CsPbI 3 nanocrystal arrays is confirmed via infrared and photoelectron spectroscopies. Untreated CsPbI 3 nanocrystal films are found to be slightly p-type with increasing conductivity achieved by incorporating the electron-accepting dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4 TCNQ) and decreasing conductivity for the electron-donating dopant benzyl viologen. Time-resolved spectroscopic measurements reveal the time scales of Auger-mediated recombination in the presence of excess electrons or holes. Microwave conductance and field-effect transistor measurements demonstrate that both the local and long-range hole mobility are improved by F 4 TCNQ doping of the nanocrystal arrays. The improved hole mobility in photoexcited p-type arrays leads to a pronounced enhancement in phototransistors.

Twelve arrays containing porphyrin, chlorin, and/or perylene-imide units were synthesized to investigate panchromatic absorption integrated with charge separation.