volatile byte buttonReleased = false;

void buttonReleasedInterrupt() {
  buttonReleased = true;
}

void setup() {
  Serial.begin(9600);
  pinMode(2, INPUT);
  attachInterrupt(digitalPinToInterrupt(1),
                  buttonReleasedInterrupt,
                  FALLING);
}
void loop() {
  if (buttonReleased) {
    buttonReleased = false;
  }
}