I have plotted the variation of concentration with time for a particular chemical. I needed to show the expotential trendline for the data. The data was filtered fom a larger dataset. I used the below code to obtain the trendlines but I am unable to add the equations and r2 value. any help will be appreciated.

dinotefuran <- filter(correlation_analysis,
                      chemical == "Dinotefuran")

dosage <- c("Single","Single","Single","Single","Single","Single","Single","Single","Single",
            "Double","Double","Double","Double","Double","Double","Double","Double","Double",
            "Single","Single","Single","Single","Single","Single",
            "Double","Double","Double","Double","Double","Double",
            "Single","Single","Single","Single","Single","Single","Single","Single","Single",
            "Double","Double","Double","Double","Double","Double","Double","Double","Double")

dinotefuran <- data.frame(dinotefuran, dosage)

Plot the variation of concentration in different matrices for Dinotefuran

ggplot(data = dinotefuran) +
  geom_point(mapping = aes(x = time_das, y = concentration_mg_by_kg, color = dosage)) +
  geom_smooth(mapping = aes(x = time_das, y = concentration_mg_by_kg, color = dosage, group = dosage),
              method = "nlsLM",
              formula = y ~ a * exp(b * x),
              se = FALSE,
              linetype = 2,
              method.args = list(start = c(a = 0.5, b = 0.2), control = nls.lm.control(maxiter = 100))) +
  facet_wrap(~ plant_part, scales = "free") +
  labs(title = "Dinotefuran Variation in Plant parts",
       x = "Time (d)",
       y = "Concentration (mg/kg)") +
  design

I tried nls method but it didnt give me the trendlines. I also want to display the confidence interval but when i change se=TRUE the trendlines are not diplayed. For the equations i tried using geom_text and stat_poly_eq but unfortunately neither of those worked.